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To:     x86@kernel.org, linux-sgx@vger.kernel.org,
        "Jarkko Sakkinen" <jarkko.sakkinen@linux.intel.com>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        "Jethro Beekman" <jethro@fortanix.com>,
        "Jordan Hand" <jorhand@linux.microsoft.com>,
        "Nathaniel McCallum" <npmccallum@redhat.com>,
        "Chunyang Hui" <sanqian.hcy@antfin.com>,
        "Seth Moore" <sethmo@google.com>,
        "Sean Christopherson" <sean.j.christopherson@intel.com>,
        akpm@linux-foundation.org, andriy.shevchenko@linux.intel.com,
        asapek@google.com, bp@alien8.de, cedric.xing@intel.com,
        chenalexchen@google.com, conradparker@google.com,
        cyhanish@google.com, dave.hansen@intel.com, haitao.huang@intel.com,
        kai.huang@intel.com, kai.svahn@intel.com, kmoy@google.com,
        ludloff@google.com, luto@kernel.org, nhorman@redhat.com,
        puiterwijk@redhat.com, rientjes@google.com, tglx@linutronix.de,
        yaozhangx@google.com, mikko.ylinen@intel.com
Subject: Re: [PATCH v39 16/24] x86/sgx: Add a page reclaimer
References: <20201003045059.665934-1-jarkko.sakkinen@linux.intel.com>
 <20201003045059.665934-17-jarkko.sakkinen@linux.intel.com>
Date:   Sat, 03 Oct 2020 00:22:47 -0500
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
From:   "Haitao Huang" <haitao.huang@linux.intel.com>
Organization: Intel Corp
Message-ID: <op.0rwbv916wjvjmi@mqcpg7oapc828.gar.corp.intel.com>
In-Reply-To: <20201003045059.665934-17-jarkko.sakkinen@linux.intel.com>
User-Agent: Opera Mail/1.0 (Win32)
Precedence: bulk

When I turn on CONFIG_PROVE_LOCKING, kernel reports following suspicious  
RCU usages. Not sure if it is an issue. Just reporting here:

[ +34.337095] =============================
[  +0.000001] WARNING: suspicious RCU usage
[  +0.000002] 5.9.0-rc6-lock-sgx39 #1 Not tainted
[  +0.000001] -----------------------------
[  +0.000001] ./include/linux/xarray.h:1165 suspicious  
rcu_dereference_check() usage!
[  +0.000001]
               other info that might help us debug this:

[  +0.000001]
               rcu_scheduler_active = 2, debug_locks = 1
[  +0.000001] 1 lock held by enclaveos-runne/4238:
[  +0.000001]  #0: ffff9cc6657e45e8 (&mm->mmap_lock#2){++++}-{3:3}, at:  
vm_mmap_pgoff+0xa1/0x120
[  +0.000005]
               stack backtrace:
[  +0.000002] CPU: 1 PID: 4238 Comm: enclaveos-runne Not tainted  
5.9.0-rc6-lock-sgx39 #1
[  +0.000001] Hardware name: Microsoft Corporation Virtual Machine/Virtual  
Machine, BIOS Hyper-V UEFI Release v4.1 04/02/2020
[  +0.000002] Call Trace:
[  +0.000003]  dump_stack+0x7d/0x9f
[  +0.000003]  lockdep_rcu_suspicious+0xce/0xf0
[  +0.000004]  xas_start+0x14c/0x1c0
[  +0.000003]  xas_load+0xf/0x50
[  +0.000002]  xas_find+0x25c/0x2c0
[  +0.000004]  sgx_encl_may_map+0x87/0x1c0
[  +0.000006]  sgx_mmap+0x29/0x70
[  +0.000003]  mmap_region+0x3ee/0x710
[  +0.000006]  do_mmap+0x3f1/0x5e0
[  +0.000004]  vm_mmap_pgoff+0xcd/0x120
[  +0.000007]  ksys_mmap_pgoff+0x1de/0x240
[  +0.000005]  __x64_sys_mmap+0x33/0x40
[  +0.000002]  do_syscall_64+0x37/0x80
[  +0.000003]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[  +0.000002] RIP: 0033:0x7fe34efe06ba
[  +0.000002] Code: 89 f5 41 54 49 89 fc 55 53 74 35 49 63 e8 48 63 da 4d  
89 f9 49 89 e8 4d 63 d6 48 89 da 4c 89 ee 4c 89 e7 b8 09 00 00 00 0f 05  
<48> 3d 00 f0 ff ff 77 56 5b 5d 41 5c 41 5d 41 5e 41 5f c3 0f 1f 00
[  +0.000001] RSP: 002b:00007ffee83eac08 EFLAGS: 00000206 ORIG_RAX:  
0000000000000009
[  +0.000001] RAX: ffffffffffffffda RBX: 0000000000000001 RCX:  
00007fe34efe06ba
[  +0.000001] RDX: 0000000000000001 RSI: 0000000000001000 RDI:  
0000000007fff000
[  +0.000001] RBP: 0000000000000004 R08: 0000000000000004 R09:  
0000000000000000
[  +0.000001] R10: 0000000000000011 R11: 0000000000000206 R12:  
0000000007fff000
[  +0.000001] R13: 0000000000001000 R14: 0000000000000011 R15:  
0000000000000000

[  +0.000010] =============================
[  +0.000001] WARNING: suspicious RCU usage
[  +0.000001] 5.9.0-rc6-lock-sgx39 #1 Not tainted
[  +0.000001] -----------------------------
[  +0.000001] ./include/linux/xarray.h:1181 suspicious  
rcu_dereference_check() usage!
[  +0.000001]
               other info that might help us debug this:

[  +0.000001]
               rcu_scheduler_active = 2, debug_locks = 1
[  +0.000001] 1 lock held by enclaveos-runne/4238:
[  +0.000001]  #0: ffff9cc6657e45e8 (&mm->mmap_lock#2){++++}-{3:3}, at:  
vm_mmap_pgoff+0xa1/0x120
[  +0.000003]
               stack backtrace:
[  +0.000001] CPU: 1 PID: 4238 Comm: enclaveos-runne Not tainted  
5.9.0-rc6-lock-sgx39 #1
[  +0.000001] Hardware name: Microsoft Corporation Virtual Machine/Virtual  
Machine, BIOS Hyper-V UEFI Release v4.1 04/02/2020
[  +0.000001] Call Trace:
[  +0.000001]  dump_stack+0x7d/0x9f
[  +0.000003]  lockdep_rcu_suspicious+0xce/0xf0
[  +0.000003]  xas_descend+0x116/0x120
[  +0.000004]  xas_load+0x42/0x50
[  +0.000002]  xas_find+0x25c/0x2c0
[  +0.000004]  sgx_encl_may_map+0x87/0x1c0
[  +0.000006]  sgx_mmap+0x29/0x70
[  +0.000002]  mmap_region+0x3ee/0x710
[  +0.000006]  do_mmap+0x3f1/0x5e0
[  +0.000004]  vm_mmap_pgoff+0xcd/0x120
[  +0.000007]  ksys_mmap_pgoff+0x1de/0x240
[  +0.000005]  __x64_sys_mmap+0x33/0x40
[  +0.000002]  do_syscall_64+0x37/0x80
[  +0.000002]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[  +0.000001] RIP: 0033:0x7fe34efe06ba
[  +0.000001] Code: 89 f5 41 54 49 89 fc 55 53 74 35 49 63 e8 48 63 da 4d  
89 f9 49 89 e8 4d 63 d6 48 89 da 4c 89 ee 4c 89 e7 b8 09 00 00 00 0f 05  
<48> 3d 00 f0 ff ff 77 56 5b 5d 41 5c 41 5d 41 5e 41 5f c3 0f 1f 00
[  +0.000001] RSP: 002b:00007ffee83eac08 EFLAGS: 00000206 ORIG_RAX:  
0000000000000009
[  +0.000001] RAX: ffffffffffffffda RBX: 0000000000000001 RCX:  
00007fe34efe06ba
[  +0.000001] RDX: 0000000000000001 RSI: 0000000000001000 RDI:  
0000000007fff000
[  +0.000001] RBP: 0000000000000004 R08: 0000000000000004 R09:  
0000000000000000
[  +0.000001] R10: 0000000000000011 R11: 0000000000000206 R12:  
0000000007fff000
[  +0.000001] R13: 0000000000001000 R14: 0000000000000011 R15:  
0000000000000000

[  +0.001117] =============================
[  +0.000001] WARNING: suspicious RCU usage
[  +0.000001] 5.9.0-rc6-lock-sgx39 #1 Not tainted
[  +0.000001] -----------------------------
[  +0.000001] ./include/linux/xarray.h:1181 suspicious  
rcu_dereference_check() usage!
[  +0.000001]
               other info that might help us debug this:

[  +0.000001]
               rcu_scheduler_active = 2, debug_locks = 1
[  +0.000001] 1 lock held by enclaveos-runne/4238:
[  +0.000001]  #0: ffff9cc6657e45e8 (&mm->mmap_lock#2){++++}-{3:3}, at:  
vm_mmap_pgoff+0xa1/0x120
[  +0.000003]
               stack backtrace:
[  +0.000002] CPU: 1 PID: 4238 Comm: enclaveos-runne Not tainted  
5.9.0-rc6-lock-sgx39 #1
[  +0.000001] Hardware name: Microsoft Corporation Virtual Machine/Virtual  
Machine, BIOS Hyper-V UEFI Release v4.1 04/02/2020
[  +0.000001] Call Trace:
[  +0.000002]  dump_stack+0x7d/0x9f
[  +0.000003]  lockdep_rcu_suspicious+0xce/0xf0
[  +0.000003]  sgx_encl_may_map+0x1b0/0x1c0
[  +0.000006]  sgx_mmap+0x29/0x70
[  +0.000002]  mmap_region+0x3ee/0x710
[  +0.000006]  do_mmap+0x3f1/0x5e0
[  +0.000005]  vm_mmap_pgoff+0xcd/0x120
[  +0.000006]  ksys_mmap_pgoff+0x1de/0x240
[  +0.000005]  __x64_sys_mmap+0x33/0x40
[  +0.000002]  do_syscall_64+0x37/0x80
[  +0.000002]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[  +0.000002] RIP: 0033:0x7fe34efe06ba
[  +0.000001] Code: 89 f5 41 54 49 89 fc 55 53 74 35 49 63 e8 48 63 da 4d  
89 f9 49 89 e8 4d 63 d6 48 89 da 4c 89 ee 4c 89 e7 b8 09 00 00 00 0f 05  
<48> 3d 00 f0 ff ff 77 56 5b 5d 41 5c 41 5d 41 5e 41 5f c3 0f 1f 00
[  +0.000001] RSP: 002b:00007ffee83eac08 EFLAGS: 00000206 ORIG_RAX:  
0000000000000009
[  +0.000001] RAX: ffffffffffffffda RBX: 0000000000000003 RCX:  
00007fe34efe06ba
[  +0.000001] RDX: 0000000000000003 RSI: 0000000000010000 RDI:  
0000000007fee000
[  +0.000001] RBP: 0000000000000004 R08: 0000000000000004 R09:  
0000000000000000
[  +0.000001] R10: 0000000000000011 R11: 0000000000000206 R12:  
0000000007fee000
[  +0.000001] R13: 0000000000010000 R14: 0000000000000011 R15:  
0000000000000000

[  +0.003197] =============================
[  +0.000001] WARNING: suspicious RCU usage
[  +0.000001] 5.9.0-rc6-lock-sgx39 #1 Not tainted
[  +0.000001] -----------------------------
[  +0.000001] ./include/linux/xarray.h:1198 suspicious  
rcu_dereference_check() usage!
[  +0.000001]
               other info that might help us debug this:

[  +0.000001]
               rcu_scheduler_active = 2, debug_locks = 1
[  +0.000001] 1 lock held by enclaveos-runne/4238:
[  +0.000001]  #0: ffff9cc6657e45e8 (&mm->mmap_lock#2){++++}-{3:3}, at:  
vm_mmap_pgoff+0xa1/0x120
[  +0.000003]
               stack backtrace:
[  +0.000002] CPU: 1 PID: 4238 Comm: enclaveos-runne Not tainted  
5.9.0-rc6-lock-sgx39 #1
[  +0.000001] Hardware name: Microsoft Corporation Virtual Machine/Virtual  
Machine, BIOS Hyper-V UEFI Release v4.1 04/02/2020
[  +0.000001] Call Trace:
[  +0.000002]  dump_stack+0x7d/0x9f
[  +0.000003]  lockdep_rcu_suspicious+0xce/0xf0
[  +0.000004]  xas_find+0x255/0x2c0
[  +0.000003]  sgx_encl_may_map+0xad/0x1c0
[  +0.000006]  sgx_mmap+0x29/0x70
[  +0.000003]  mmap_region+0x3ee/0x710
[  +0.000005]  do_mmap+0x3f1/0x5e0
[  +0.000005]  vm_mmap_pgoff+0xcd/0x120
[  +0.000007]  ksys_mmap_pgoff+0x1de/0x240
[  +0.000004]  __x64_sys_mmap+0x33/0x40
[  +0.000002]  do_syscall_64+0x37/0x80
[  +0.000002]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[  +0.000002] RIP: 0033:0x7fe34efe06ba
[  +0.000001] Code: 89 f5 41 54 49 89 fc 55 53 74 35 49 63 e8 48 63 da 4d  
89 f9 49 89 e8 4d 63 d6 48 89 da 4c 89 ee 4c 89 e7 b8 09 00 00 00 0f 05  
<48> 3d 00 f0 ff ff 77 56 5b 5d 41 5c 41 5d 41 5e 41 5f c3 0f 1f 00
[  +0.000001] RSP: 002b:00007ffee83eac08 EFLAGS: 00000206 ORIG_RAX:  
0000000000000009
[  +0.000002] RAX: ffffffffffffffda RBX: 0000000000000003 RCX:  
00007fe34efe06ba
[  +0.000001] RDX: 0000000000000003 RSI: 0000000000010000 RDI:  
0000000007fba000
[  +0.000001] RBP: 0000000000000004 R08: 0000000000000004 R09:  
0000000000000000
[  +0.000001] R10: 0000000000000011 R11: 0000000000000206 R12:  
0000000007fba000
[  +0.000001] R13: 0000000000010000 R14: 0000000000000011 R15:  
0000000000000000


On Fri, 02 Oct 2020 23:50:51 -0500, Jarkko Sakkinen  
<jarkko.sakkinen@linux.intel.com> wrote:

> There is a limited amount of EPC available. Therefore, some of it must be
> copied to the regular memory, and only subset kept in the SGX reserved
> memory. While kernel cannot directly access enclave memory, SGX provides  
> a
> set of ENCLS leaf functions to perform reclaiming.
>
> Implement a page reclaimer by using these leaf functions. It picks the
> victim pages in LRU fashion from all the enclaves running in the system.
> The thread ksgxswapd reclaims pages on the event when the number of free
> EPC pages goes below SGX_NR_LOW_PAGES up until it reaches
> SGX_NR_HIGH_PAGES.
>
> sgx_alloc_epc_page() can optionally directly reclaim pages with @reclaim
> set true. A caller must also supply owner for each page so that the
> reclaimer can access the associated enclaves. This is needed for locking,
> as most of the ENCLS leafs cannot be executed concurrently for an  
> enclave.
> The owner is also needed for accessing SECS, which is required to be
> resident when its child pages are being reclaimed.
>
> Cc: linux-mm@kvack.org
> Acked-by: Jethro Beekman <jethro@fortanix.com>
> Tested-by: Jethro Beekman <jethro@fortanix.com>
> Tested-by: Jordan Hand <jorhand@linux.microsoft.com>
> Tested-by: Nathaniel McCallum <npmccallum@redhat.com>
> Tested-by: Chunyang Hui <sanqian.hcy@antfin.com>
> Tested-by: Seth Moore <sethmo@google.com>
> Co-developed-by: Sean Christopherson <sean.j.christopherson@intel.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
> ---
>  arch/x86/kernel/cpu/sgx/driver.c |   1 +
>  arch/x86/kernel/cpu/sgx/encl.c   | 344 +++++++++++++++++++++-
>  arch/x86/kernel/cpu/sgx/encl.h   |  41 +++
>  arch/x86/kernel/cpu/sgx/ioctl.c  |  78 ++++-
>  arch/x86/kernel/cpu/sgx/main.c   | 481 +++++++++++++++++++++++++++++++
>  arch/x86/kernel/cpu/sgx/sgx.h    |   9 +
>  6 files changed, 947 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/sgx/driver.c  
> b/arch/x86/kernel/cpu/sgx/driver.c
> index d01b28f7ce4a..0446781cc7a2 100644
> --- a/arch/x86/kernel/cpu/sgx/driver.c
> +++ b/arch/x86/kernel/cpu/sgx/driver.c
> @@ -29,6 +29,7 @@ static int sgx_open(struct inode *inode, struct file  
> *file)
>  	atomic_set(&encl->flags, 0);
>  	kref_init(&encl->refcount);
>  	xa_init(&encl->page_array);
> +	INIT_LIST_HEAD(&encl->va_pages);
>  	mutex_init(&encl->lock);
>  	INIT_LIST_HEAD(&encl->mm_list);
>  	spin_lock_init(&encl->mm_lock);
> diff --git a/arch/x86/kernel/cpu/sgx/encl.c  
> b/arch/x86/kernel/cpu/sgx/encl.c
> index c2c4a77af36b..54326efa6c2f 100644
> --- a/arch/x86/kernel/cpu/sgx/encl.c
> +++ b/arch/x86/kernel/cpu/sgx/encl.c
> @@ -12,9 +12,88 @@
>  #include "encls.h"
>  #include "sgx.h"
> +/*
> + * ELDU: Load an EPC page as unblocked. For more info, see "OS  
> Management of EPC
> + * Pages" in the SDM.
> + */
> +static int __sgx_encl_eldu(struct sgx_encl_page *encl_page,
> +			   struct sgx_epc_page *epc_page,
> +			   struct sgx_epc_page *secs_page)
> +{
> +	unsigned long va_offset = SGX_ENCL_PAGE_VA_OFFSET(encl_page);
> +	struct sgx_encl *encl = encl_page->encl;
> +	struct sgx_pageinfo pginfo;
> +	struct sgx_backing b;
> +	pgoff_t page_index;
> +	int ret;
> +
> +	if (secs_page)
> +		page_index = SGX_ENCL_PAGE_INDEX(encl_page);
> +	else
> +		page_index = PFN_DOWN(encl->size);
> +
> +	ret = sgx_encl_get_backing(encl, page_index, &b);
> +	if (ret)
> +		return ret;
> +
> +	pginfo.addr = SGX_ENCL_PAGE_ADDR(encl_page);
> +	pginfo.contents = (unsigned long)kmap_atomic(b.contents);
> +	pginfo.metadata = (unsigned long)kmap_atomic(b.pcmd) +
> +			  b.pcmd_offset;
> +
> +	if (secs_page)
> +		pginfo.secs = (u64)sgx_get_epc_addr(secs_page);
> +	else
> +		pginfo.secs = 0;
> +
> +	ret = __eldu(&pginfo, sgx_get_epc_addr(epc_page),
> +		     sgx_get_epc_addr(encl_page->va_page->epc_page) +
> +				      va_offset);
> +	if (ret) {
> +		if (encls_failed(ret))
> +			ENCLS_WARN(ret, "ELDU");
> +
> +		ret = -EFAULT;
> +	}
> +
> +	kunmap_atomic((void *)(unsigned long)(pginfo.metadata -  
> b.pcmd_offset));
> +	kunmap_atomic((void *)(unsigned long)pginfo.contents);
> +
> +	sgx_encl_put_backing(&b, false);
> +
> +	return ret;
> +}
> +
> +static struct sgx_epc_page *sgx_encl_eldu(struct sgx_encl_page  
> *encl_page,
> +					  struct sgx_epc_page *secs_page)
> +{
> +	unsigned long va_offset = SGX_ENCL_PAGE_VA_OFFSET(encl_page);
> +	struct sgx_encl *encl = encl_page->encl;
> +	struct sgx_epc_page *epc_page;
> +	int ret;
> +
> +	epc_page = sgx_alloc_epc_page(encl_page, false);
> +	if (IS_ERR(epc_page))
> +		return epc_page;
> +
> +	ret = __sgx_encl_eldu(encl_page, epc_page, secs_page);
> +	if (ret) {
> +		sgx_free_epc_page(epc_page);
> +		return ERR_PTR(ret);
> +	}
> +
> +	sgx_free_va_slot(encl_page->va_page, va_offset);
> +	list_move(&encl_page->va_page->list, &encl->va_pages);
> +	encl_page->desc &= ~SGX_ENCL_PAGE_VA_OFFSET_MASK;
> +	encl_page->epc_page = epc_page;
> +
> +	return epc_page;
> +}
> +
>  static struct sgx_encl_page *sgx_encl_load_page(struct sgx_encl *encl,
>  						unsigned long addr)
>  {
> +	struct sgx_epc_page *epc_page;
>  	struct sgx_encl_page *entry;
>  	unsigned int flags;
> @@ -33,10 +112,27 @@ static struct sgx_encl_page  
> *sgx_encl_load_page(struct sgx_encl *encl,
>  		return ERR_PTR(-EFAULT);
> 	/* Page is already resident in the EPC. */
> -	if (entry->epc_page)
> +	if (entry->epc_page) {
> +		if (entry->desc & SGX_ENCL_PAGE_BEING_RECLAIMED)
> +			return ERR_PTR(-EBUSY);
> +
>  		return entry;
> +	}
> +
> +	if (!(encl->secs.epc_page)) {
> +		epc_page = sgx_encl_eldu(&encl->secs, NULL);
> +		if (IS_ERR(epc_page))
> +			return ERR_CAST(epc_page);
> +	}
> -	return ERR_PTR(-EFAULT);
> +	epc_page = sgx_encl_eldu(entry, encl->secs.epc_page);
> +	if (IS_ERR(epc_page))
> +		return ERR_CAST(epc_page);
> +
> +	encl->secs_child_cnt++;
> +	sgx_mark_page_reclaimable(entry->epc_page);
> +
> +	return entry;
>  }
> static void sgx_mmu_notifier_release(struct mmu_notifier *mn,
> @@ -132,6 +228,9 @@ int sgx_encl_mm_add(struct sgx_encl *encl, struct  
> mm_struct *mm)
> 	spin_lock(&encl->mm_lock);
>  	list_add_rcu(&encl_mm->list, &encl->mm_list);
> +	/* Pairs with smp_rmb() in sgx_reclaimer_block(). */
> +	smp_wmb();
> +	encl->mm_list_version++;
>  	spin_unlock(&encl->mm_lock);
> 	return 0;
> @@ -179,6 +278,8 @@ static unsigned int sgx_vma_fault(struct vm_fault  
> *vmf)
>  		goto out;
>  	}
> +	sgx_encl_test_and_clear_young(vma->vm_mm, entry);
> +
>  out:
>  	mutex_unlock(&encl->lock);
>  	return ret;
> @@ -280,6 +381,7 @@ int sgx_encl_find(struct mm_struct *mm, unsigned  
> long addr,
>   */
>  void sgx_encl_destroy(struct sgx_encl *encl)
>  {
> +	struct sgx_va_page *va_page;
>  	struct sgx_encl_page *entry;
>  	unsigned long index;
> @@ -287,6 +389,13 @@ void sgx_encl_destroy(struct sgx_encl *encl)
> 	xa_for_each(&encl->page_array, index, entry) {
>  		if (entry->epc_page) {
> +			/*
> +			 * The page and its radix tree entry cannot be freed
> +			 * if the page is being held by the reclaimer.
> +			 */
> +			if (sgx_unmark_page_reclaimable(entry->epc_page))
> +				continue;
> +
>  			sgx_free_epc_page(entry->epc_page);
>  			encl->secs_child_cnt--;
>  			entry->epc_page = NULL;
> @@ -301,6 +410,19 @@ void sgx_encl_destroy(struct sgx_encl *encl)
>  		sgx_free_epc_page(encl->secs.epc_page);
>  		encl->secs.epc_page = NULL;
>  	}
> +
> +	/*
> +	 * The reclaimer is responsible for checking SGX_ENCL_DEAD before doing
> +	 * EWB, thus it's safe to free VA pages even if the reclaimer holds a
> +	 * reference to the enclave.
> +	 */
> +	while (!list_empty(&encl->va_pages)) {
> +		va_page = list_first_entry(&encl->va_pages, struct sgx_va_page,
> +					   list);
> +		list_del(&va_page->list);
> +		sgx_free_epc_page(va_page->epc_page);
> +		kfree(va_page);
> +	}
>  }
> /**
> @@ -329,3 +451,221 @@ void sgx_encl_release(struct kref *ref)
> 	kfree(encl);
>  }
> +
> +static struct page *sgx_encl_get_backing_page(struct sgx_encl *encl,
> +					      pgoff_t index)
> +{
> +	struct inode *inode = encl->backing->f_path.dentry->d_inode;
> +	struct address_space *mapping = inode->i_mapping;
> +	gfp_t gfpmask = mapping_gfp_mask(mapping);
> +
> +	return shmem_read_mapping_page_gfp(mapping, index, gfpmask);
> +}
> +
> +/**
> + * sgx_encl_get_backing() - Pin the backing storage
> + * @encl:	an enclave pointer
> + * @page_index:	enclave page index
> + * @backing:	data for accessing backing storage for the page
> + *
> + * Pin the backing storage pages for storing the encrypted contents and  
> Paging
> + * Crypto MetaData (PCMD) of an enclave page.
> + *
> + * Return:
> + *   0 on success,
> + *   -errno otherwise.
> + */
> +int sgx_encl_get_backing(struct sgx_encl *encl, unsigned long  
> page_index,
> +			 struct sgx_backing *backing)
> +{
> +	pgoff_t pcmd_index = PFN_DOWN(encl->size) + 1 + (page_index >> 5);
> +	struct page *contents;
> +	struct page *pcmd;
> +
> +	contents = sgx_encl_get_backing_page(encl, page_index);
> +	if (IS_ERR(contents))
> +		return PTR_ERR(contents);
> +
> +	pcmd = sgx_encl_get_backing_page(encl, pcmd_index);
> +	if (IS_ERR(pcmd)) {
> +		put_page(contents);
> +		return PTR_ERR(pcmd);
> +	}
> +
> +	backing->page_index = page_index;
> +	backing->contents = contents;
> +	backing->pcmd = pcmd;
> +	backing->pcmd_offset =
> +		(page_index & (PAGE_SIZE / sizeof(struct sgx_pcmd) - 1)) *
> +		sizeof(struct sgx_pcmd);
> +
> +	return 0;
> +}
> +
> +/**
> + * sgx_encl_put_backing() - Unpin the backing storage
> + * @backing:	data for accessing backing storage for the page
> + * @do_write:	mark pages dirty
> + */
> +void sgx_encl_put_backing(struct sgx_backing *backing, bool do_write)
> +{
> +	if (do_write) {
> +		set_page_dirty(backing->pcmd);
> +		set_page_dirty(backing->contents);
> +	}
> +
> +	put_page(backing->pcmd);
> +	put_page(backing->contents);
> +}
> +
> +static int sgx_encl_test_and_clear_young_cb(pte_t *ptep, unsigned long  
> addr,
> +					    void *data)
> +{
> +	pte_t pte;
> +	int ret;
> +
> +	ret = pte_young(*ptep);
> +	if (ret) {
> +		pte = pte_mkold(*ptep);
> +		set_pte_at((struct mm_struct *)data, addr, ptep, pte);
> +	}
> +
> +	return ret;
> +}
> +
> +/**
> + * sgx_encl_test_and_clear_young() - Test and reset the accessed bit
> + * @mm:		mm_struct that is checked
> + * @page:	enclave page to be tested for recent access
> + *
> + * Checks the Access (A) bit from the PTE corresponding to the enclave  
> page and
> + * clears it.
> + *
> + * Return: 1 if the page has been recently accessed and 0 if not.
> + */
> +int sgx_encl_test_and_clear_young(struct mm_struct *mm,
> +				  struct sgx_encl_page *page)
> +{
> +	unsigned long addr = SGX_ENCL_PAGE_ADDR(page);
> +	struct sgx_encl *encl = page->encl;
> +	struct vm_area_struct *vma;
> +	int ret;
> +
> +	ret = sgx_encl_find(mm, addr, &vma);
> +	if (ret)
> +		return 0;
> +
> +	if (encl != vma->vm_private_data)
> +		return 0;
> +
> +	ret = apply_to_page_range(vma->vm_mm, addr, PAGE_SIZE,
> +				  sgx_encl_test_and_clear_young_cb, vma->vm_mm);
> +	if (ret < 0)
> +		return 0;
> +
> +	return ret;
> +}
> +
> +/**
> + * sgx_encl_reserve_page() - Reserve an enclave page
> + * @encl:	an enclave pointer
> + * @addr:	a page address
> + *
> + * Load an enclave page and lock the enclave so that the page can be  
> used by
> + * EDBG* and EMOD*.
> + *
> + * Return:
> + *   an enclave page on success
> + *   -EFAULT	if the load fails
> + */
> +struct sgx_encl_page *sgx_encl_reserve_page(struct sgx_encl *encl,
> +					    unsigned long addr)
> +{
> +	struct sgx_encl_page *entry;
> +
> +	for ( ; ; ) {
> +		mutex_lock(&encl->lock);
> +
> +		entry = sgx_encl_load_page(encl, addr);
> +		if (PTR_ERR(entry) != -EBUSY)
> +			break;
> +
> +		mutex_unlock(&encl->lock);
> +	}
> +
> +	if (IS_ERR(entry))
> +		mutex_unlock(&encl->lock);
> +
> +	return entry;
> +}
> +
> +/**
> + * sgx_alloc_va_page() - Allocate a Version Array (VA) page
> + *
> + * Allocate a free EPC page and convert it to a Version Array (VA) page.
> + *
> + * Return:
> + *   a VA page,
> + *   -errno otherwise
> + */
> +struct sgx_epc_page *sgx_alloc_va_page(void)
> +{
> +	struct sgx_epc_page *epc_page;
> +	int ret;
> +
> +	epc_page = sgx_alloc_epc_page(NULL, true);
> +	if (IS_ERR(epc_page))
> +		return ERR_CAST(epc_page);
> +
> +	ret = __epa(sgx_get_epc_addr(epc_page));
> +	if (ret) {
> +		WARN_ONCE(1, "EPA returned %d (0x%x)", ret, ret);
> +		sgx_free_epc_page(epc_page);
> +		return ERR_PTR(-EFAULT);
> +	}
> +
> +	return epc_page;
> +}
> +
> +/**
> + * sgx_alloc_va_slot - allocate a VA slot
> + * @va_page:	a &struct sgx_va_page instance
> + *
> + * Allocates a slot from a &struct sgx_va_page instance.
> + *
> + * Return: offset of the slot inside the VA page
> + */
> +unsigned int sgx_alloc_va_slot(struct sgx_va_page *va_page)
> +{
> +	int slot = find_first_zero_bit(va_page->slots, SGX_VA_SLOT_COUNT);
> +
> +	if (slot < SGX_VA_SLOT_COUNT)
> +		set_bit(slot, va_page->slots);
> +
> +	return slot << 3;
> +}
> +
> +/**
> + * sgx_free_va_slot - free a VA slot
> + * @va_page:	a &struct sgx_va_page instance
> + * @offset:	offset of the slot inside the VA page
> + *
> + * Frees a slot from a &struct sgx_va_page instance.
> + */
> +void sgx_free_va_slot(struct sgx_va_page *va_page, unsigned int offset)
> +{
> +	clear_bit(offset >> 3, va_page->slots);
> +}
> +
> +/**
> + * sgx_va_page_full - is the VA page full?
> + * @va_page:	a &struct sgx_va_page instance
> + *
> + * Return: true if all slots have been taken
> + */
> +bool sgx_va_page_full(struct sgx_va_page *va_page)
> +{
> +	int slot = find_first_zero_bit(va_page->slots, SGX_VA_SLOT_COUNT);
> +
> +	return slot == SGX_VA_SLOT_COUNT;
> +}
> diff --git a/arch/x86/kernel/cpu/sgx/encl.h  
> b/arch/x86/kernel/cpu/sgx/encl.h
> index 0448d22d3010..e8eb9e9a834e 100644
> --- a/arch/x86/kernel/cpu/sgx/encl.h
> +++ b/arch/x86/kernel/cpu/sgx/encl.h
> @@ -19,6 +19,10 @@
> /**
>   * enum sgx_encl_page_desc - defines bits for an enclave page's  
> descriptor
> + * %SGX_ENCL_PAGE_BEING_RECLAIMED:	The page is in the process of being
> + *					reclaimed.
> + * %SGX_ENCL_PAGE_VA_OFFSET_MASK:	Holds the offset in the Version Array
> + *					(VA) page for a swapped page.
>   * %SGX_ENCL_PAGE_ADDR_MASK:		Holds the virtual address of the page.
>   *
>   * The page address for SECS is zero and is used by the subsystem to  
> recognize
> @@ -26,16 +30,23 @@
>   */
>  enum sgx_encl_page_desc {
>  	/* Bits 11:3 are available when the page is not swapped. */
> +	SGX_ENCL_PAGE_BEING_RECLAIMED		= BIT(3),
> +	SGX_ENCL_PAGE_VA_OFFSET_MASK	= GENMASK_ULL(11, 3),
>  	SGX_ENCL_PAGE_ADDR_MASK		= PAGE_MASK,
>  };
> #define SGX_ENCL_PAGE_ADDR(page) \
>  	((page)->desc & SGX_ENCL_PAGE_ADDR_MASK)
> +#define SGX_ENCL_PAGE_VA_OFFSET(page) \
> +	((page)->desc & SGX_ENCL_PAGE_VA_OFFSET_MASK)
> +#define SGX_ENCL_PAGE_INDEX(page) \
> +	PFN_DOWN((page)->desc - (page)->encl->base)
> struct sgx_encl_page {
>  	unsigned long desc;
>  	unsigned long vm_max_prot_bits;
>  	struct sgx_epc_page *epc_page;
> +	struct sgx_va_page *va_page;
>  	struct sgx_encl *encl;
>  };
> @@ -61,6 +72,7 @@ struct sgx_encl {
>  	struct mutex lock;
>  	struct list_head mm_list;
>  	spinlock_t mm_lock;
> +	unsigned long mm_list_version;
>  	struct file *backing;
>  	struct kref refcount;
>  	struct srcu_struct srcu;
> @@ -68,12 +80,21 @@ struct sgx_encl {
>  	unsigned long size;
>  	unsigned long ssaframesize;
>  	struct xarray page_array;
> +	struct list_head va_pages;
>  	struct sgx_encl_page secs;
>  	cpumask_t cpumask;
>  	unsigned long attributes;
>  	unsigned long attributes_mask;
>  };
> +#define SGX_VA_SLOT_COUNT 512
> +
> +struct sgx_va_page {
> +	struct sgx_epc_page *epc_page;
> +	DECLARE_BITMAP(slots, SGX_VA_SLOT_COUNT);
> +	struct list_head list;
> +};
> +
>  extern const struct vm_operations_struct sgx_vm_ops;
> int sgx_encl_find(struct mm_struct *mm, unsigned long addr,
> @@ -84,4 +105,24 @@ int sgx_encl_mm_add(struct sgx_encl *encl, struct  
> mm_struct *mm);
>  int sgx_encl_may_map(struct sgx_encl *encl, unsigned long start,
>  		     unsigned long end, unsigned long vm_flags);
> +struct sgx_backing {
> +	pgoff_t page_index;
> +	struct page *contents;
> +	struct page *pcmd;
> +	unsigned long pcmd_offset;
> +};
> +
> +int sgx_encl_get_backing(struct sgx_encl *encl, unsigned long  
> page_index,
> +			 struct sgx_backing *backing);
> +void sgx_encl_put_backing(struct sgx_backing *backing, bool do_write);
> +int sgx_encl_test_and_clear_young(struct mm_struct *mm,
> +				  struct sgx_encl_page *page);
> +struct sgx_encl_page *sgx_encl_reserve_page(struct sgx_encl *encl,
> +					    unsigned long addr);
> +
> +struct sgx_epc_page *sgx_alloc_va_page(void);
> +unsigned int sgx_alloc_va_slot(struct sgx_va_page *va_page);
> +void sgx_free_va_slot(struct sgx_va_page *va_page, unsigned int offset);
> +bool sgx_va_page_full(struct sgx_va_page *va_page);
> +
>  #endif /* _X86_ENCL_H */
> diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c  
> b/arch/x86/kernel/cpu/sgx/ioctl.c
> index 3c04798e83e5..613f6c03598e 100644
> --- a/arch/x86/kernel/cpu/sgx/ioctl.c
> +++ b/arch/x86/kernel/cpu/sgx/ioctl.c
> @@ -16,6 +16,43 @@
>  #include "encl.h"
>  #include "encls.h"
> +static struct sgx_va_page *sgx_encl_grow(struct sgx_encl *encl)
> +{
> +	struct sgx_va_page *va_page = NULL;
> +	void *err;
> +
> +	BUILD_BUG_ON(SGX_VA_SLOT_COUNT !=
> +		(SGX_ENCL_PAGE_VA_OFFSET_MASK >> 3) + 1);
> +
> +	if (!(encl->page_cnt % SGX_VA_SLOT_COUNT)) {
> +		va_page = kzalloc(sizeof(*va_page), GFP_KERNEL);
> +		if (!va_page)
> +			return ERR_PTR(-ENOMEM);
> +
> +		va_page->epc_page = sgx_alloc_va_page();
> +		if (IS_ERR(va_page->epc_page)) {
> +			err = ERR_CAST(va_page->epc_page);
> +			kfree(va_page);
> +			return err;
> +		}
> +
> +		WARN_ON_ONCE(encl->page_cnt % SGX_VA_SLOT_COUNT);
> +	}
> +	encl->page_cnt++;
> +	return va_page;
> +}
> +
> +static void sgx_encl_shrink(struct sgx_encl *encl, struct sgx_va_page  
> *va_page)
> +{
> +	encl->page_cnt--;
> +
> +	if (va_page) {
> +		sgx_free_epc_page(va_page->epc_page);
> +		list_del(&va_page->list);
> +		kfree(va_page);
> +	}
> +}
> +
>  static u32 sgx_calc_ssa_frame_size(u32 miscselect, u64 xfrm)
>  {
>  	u32 size_max = PAGE_SIZE;
> @@ -80,15 +117,24 @@ static int sgx_validate_secs(const struct sgx_secs  
> *secs)
>  static int sgx_encl_create(struct sgx_encl *encl, struct sgx_secs *secs)
>  {
>  	struct sgx_epc_page *secs_epc;
> +	struct sgx_va_page *va_page;
>  	struct sgx_pageinfo pginfo;
>  	struct sgx_secinfo secinfo;
>  	unsigned long encl_size;
>  	struct file *backing;
>  	long ret;
> +	va_page = sgx_encl_grow(encl);
> +	if (IS_ERR(va_page))
> +		return PTR_ERR(va_page);
> +	else if (va_page)
> +		list_add(&va_page->list, &encl->va_pages);
> +	/* else the tail page of the VA page list had free slots. */
> +
>  	if (sgx_validate_secs(secs)) {
>  		pr_debug("invalid SECS\n");
> -		return -EINVAL;
> +		ret = -EINVAL;
> +		goto err_out_shrink;
>  	}
> 	/* The extra page goes to SECS. */
> @@ -96,12 +142,14 @@ static int sgx_encl_create(struct sgx_encl *encl,  
> struct sgx_secs *secs)
> 	backing = shmem_file_setup("SGX backing", encl_size + (encl_size >> 5),
>  				   VM_NORESERVE);
> -	if (IS_ERR(backing))
> -		return PTR_ERR(backing);
> +	if (IS_ERR(backing)) {
> +		ret = PTR_ERR(backing);
> +		goto err_out_shrink;
> +	}
> 	encl->backing = backing;
> -	secs_epc = __sgx_alloc_epc_page();
> +	secs_epc = sgx_alloc_epc_page(&encl->secs, true);
>  	if (IS_ERR(secs_epc)) {
>  		ret = PTR_ERR(secs_epc);
>  		goto err_out_backing;
> @@ -149,6 +197,9 @@ static int sgx_encl_create(struct sgx_encl *encl,  
> struct sgx_secs *secs)
>  	fput(encl->backing);
>  	encl->backing = NULL;
> +err_out_shrink:
> +	sgx_encl_shrink(encl, va_page);
> +
>  	return ret;
>  }
> @@ -321,21 +372,35 @@ static int sgx_encl_add_page(struct sgx_encl  
> *encl, unsigned long src,
>  {
>  	struct sgx_encl_page *encl_page;
>  	struct sgx_epc_page *epc_page;
> +	struct sgx_va_page *va_page;
>  	int ret;
> 	encl_page = sgx_encl_page_alloc(encl, offset, secinfo->flags);
>  	if (IS_ERR(encl_page))
>  		return PTR_ERR(encl_page);
> -	epc_page = __sgx_alloc_epc_page();
> +	epc_page = sgx_alloc_epc_page(encl_page, true);
>  	if (IS_ERR(epc_page)) {
>  		kfree(encl_page);
>  		return PTR_ERR(epc_page);
>  	}
> +	va_page = sgx_encl_grow(encl);
> +	if (IS_ERR(va_page)) {
> +		ret = PTR_ERR(va_page);
> +		goto err_out_free;
> +	}
> +
>  	mmap_read_lock(current->mm);
>  	mutex_lock(&encl->lock);
> +	/*
> +	 * Adding to encl->va_pages must be done under encl->lock.  Ditto for
> +	 * deleting (via sgx_encl_shrink()) in the error path.
> +	 */
> +	if (va_page)
> +		list_add(&va_page->list, &encl->va_pages);
> +
>  	/*
>  	 * Insert prior to EADD in case of OOM.  EADD modifies MRENCLAVE, i.e.
>  	 * can't be gracefully unwound, while failure on EADD/EXTEND is limited
> @@ -366,6 +431,7 @@ static int sgx_encl_add_page(struct sgx_encl *encl,  
> unsigned long src,
>  			goto err_out;
>  	}
> +	sgx_mark_page_reclaimable(encl_page->epc_page);
>  	mutex_unlock(&encl->lock);
>  	mmap_read_unlock(current->mm);
>  	return ret;
> @@ -374,9 +440,11 @@ static int sgx_encl_add_page(struct sgx_encl *encl,  
> unsigned long src,
>  	xa_erase(&encl->page_array, PFN_DOWN(encl_page->desc));
> err_out_unlock:
> +	sgx_encl_shrink(encl, va_page);
>  	mutex_unlock(&encl->lock);
>  	mmap_read_unlock(current->mm);
> +err_out_free:
>  	sgx_free_epc_page(epc_page);
>  	kfree(encl_page);
> diff --git a/arch/x86/kernel/cpu/sgx/main.c  
> b/arch/x86/kernel/cpu/sgx/main.c
> index 4137254fb29e..3f9130501370 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -16,6 +16,395 @@
>  struct sgx_epc_section sgx_epc_sections[SGX_MAX_EPC_SECTIONS];
>  static int sgx_nr_epc_sections;
>  static struct task_struct *ksgxswapd_tsk;
> +static DECLARE_WAIT_QUEUE_HEAD(ksgxswapd_waitq);
> +static LIST_HEAD(sgx_active_page_list);
> +static DEFINE_SPINLOCK(sgx_active_page_list_lock);
> +
> +/**
> + * sgx_mark_page_reclaimable() - Mark a page as reclaimable
> + * @page:	EPC page
> + *
> + * Mark a page as reclaimable and add it to the active page list. Pages
> + * are automatically removed from the active list when freed.
> + */
> +void sgx_mark_page_reclaimable(struct sgx_epc_page *page)
> +{
> +	spin_lock(&sgx_active_page_list_lock);
> +	page->desc |= SGX_EPC_PAGE_RECLAIMABLE;
> +	list_add_tail(&page->list, &sgx_active_page_list);
> +	spin_unlock(&sgx_active_page_list_lock);
> +}
> +
> +/**
> + * sgx_unmark_page_reclaimable() - Remove a page from the reclaim list
> + * @page:	EPC page
> + *
> + * Clear the reclaimable flag and remove the page from the active page  
> list.
> + *
> + * Return:
> + *   0 on success,
> + *   -EBUSY if the page is in the process of being reclaimed
> + */
> +int sgx_unmark_page_reclaimable(struct sgx_epc_page *page)
> +{
> +	/*
> +	 * Remove the page from the active list if necessary.  If the page
> +	 * is actively being reclaimed, i.e. RECLAIMABLE is set but the
> +	 * page isn't on the active list, return -EBUSY as we can't free
> +	 * the page at this time since it is "owned" by the reclaimer.
> +	 */
> +	spin_lock(&sgx_active_page_list_lock);
> +	if (page->desc & SGX_EPC_PAGE_RECLAIMABLE) {
> +		if (list_empty(&page->list)) {
> +			spin_unlock(&sgx_active_page_list_lock);
> +			return -EBUSY;
> +		}
> +		list_del(&page->list);
> +		page->desc &= ~SGX_EPC_PAGE_RECLAIMABLE;
> +	}
> +	spin_unlock(&sgx_active_page_list_lock);
> +
> +	return 0;
> +}
> +
> +static bool sgx_reclaimer_age(struct sgx_epc_page *epc_page)
> +{
> +	struct sgx_encl_page *page = epc_page->owner;
> +	struct sgx_encl *encl = page->encl;
> +	struct sgx_encl_mm *encl_mm;
> +	bool ret = true;
> +	int idx;
> +
> +	idx = srcu_read_lock(&encl->srcu);
> +
> +	list_for_each_entry_rcu(encl_mm, &encl->mm_list, list) {
> +		if (!mmget_not_zero(encl_mm->mm))
> +			continue;
> +
> +		mmap_read_lock(encl_mm->mm);
> +		ret = !sgx_encl_test_and_clear_young(encl_mm->mm, page);
> +		mmap_read_unlock(encl_mm->mm);
> +
> +		mmput_async(encl_mm->mm);
> +
> +		if (!ret || (atomic_read(&encl->flags) & SGX_ENCL_DEAD))
> +			break;
> +	}
> +
> +	srcu_read_unlock(&encl->srcu, idx);
> +
> +	if (!ret && !(atomic_read(&encl->flags) & SGX_ENCL_DEAD))
> +		return false;
> +
> +	return true;
> +}
> +
> +static void sgx_reclaimer_block(struct sgx_epc_page *epc_page)
> +{
> +	struct sgx_encl_page *page = epc_page->owner;
> +	unsigned long addr = SGX_ENCL_PAGE_ADDR(page);
> +	struct sgx_encl *encl = page->encl;
> +	unsigned long mm_list_version;
> +	struct sgx_encl_mm *encl_mm;
> +	struct vm_area_struct *vma;
> +	int idx, ret;
> +
> +	do {
> +		mm_list_version = encl->mm_list_version;
> +
> +		/* Pairs with smp_rmb() in sgx_encl_mm_add(). */
> +		smp_rmb();
> +
> +		idx = srcu_read_lock(&encl->srcu);
> +
> +		list_for_each_entry_rcu(encl_mm, &encl->mm_list, list) {
> +			if (!mmget_not_zero(encl_mm->mm))
> +				continue;
> +
> +			mmap_read_lock(encl_mm->mm);
> +
> +			ret = sgx_encl_find(encl_mm->mm, addr, &vma);
> +			if (!ret && encl == vma->vm_private_data)
> +				zap_vma_ptes(vma, addr, PAGE_SIZE);
> +
> +			mmap_read_unlock(encl_mm->mm);
> +
> +			mmput_async(encl_mm->mm);
> +		}
> +
> +		srcu_read_unlock(&encl->srcu, idx);
> +	} while (unlikely(encl->mm_list_version != mm_list_version));
> +
> +	mutex_lock(&encl->lock);
> +
> +	if (!(atomic_read(&encl->flags) & SGX_ENCL_DEAD)) {
> +		ret = __eblock(sgx_get_epc_addr(epc_page));
> +		if (encls_failed(ret))
> +			ENCLS_WARN(ret, "EBLOCK");
> +	}
> +
> +	mutex_unlock(&encl->lock);
> +}
> +
> +static int __sgx_encl_ewb(struct sgx_epc_page *epc_page, void *va_slot,
> +			  struct sgx_backing *backing)
> +{
> +	struct sgx_pageinfo pginfo;
> +	int ret;
> +
> +	pginfo.addr = 0;
> +	pginfo.secs = 0;
> +
> +	pginfo.contents = (unsigned long)kmap_atomic(backing->contents);
> +	pginfo.metadata = (unsigned long)kmap_atomic(backing->pcmd) +
> +			  backing->pcmd_offset;
> +
> +	ret = __ewb(&pginfo, sgx_get_epc_addr(epc_page), va_slot);
> +
> +	kunmap_atomic((void *)(unsigned long)(pginfo.metadata -
> +					      backing->pcmd_offset));
> +	kunmap_atomic((void *)(unsigned long)pginfo.contents);
> +
> +	return ret;
> +}
> +
> +static void sgx_ipi_cb(void *info)
> +{
> +}
> +
> +static const cpumask_t *sgx_encl_ewb_cpumask(struct sgx_encl *encl)
> +{
> +	cpumask_t *cpumask = &encl->cpumask;
> +	struct sgx_encl_mm *encl_mm;
> +	int idx;
> +
> +	/*
> +	 * Can race with sgx_encl_mm_add(), but ETRACK has already been
> +	 * executed, which means that the CPUs running in the new mm will enter
> +	 * into the enclave with a fresh epoch.
> +	 */
> +	cpumask_clear(cpumask);
> +
> +	idx = srcu_read_lock(&encl->srcu);
> +
> +	list_for_each_entry_rcu(encl_mm, &encl->mm_list, list) {
> +		if (!mmget_not_zero(encl_mm->mm))
> +			continue;
> +
> +		cpumask_or(cpumask, cpumask, mm_cpumask(encl_mm->mm));
> +
> +		mmput_async(encl_mm->mm);
> +	}
> +
> +	srcu_read_unlock(&encl->srcu, idx);
> +
> +	return cpumask;
> +}
> +
> +/*
> + * Swap page to the regular memory transformed to the blocked state by  
> using
> + * EBLOCK, which means that it can no loger be referenced (no new TLB  
> entries).
> + *
> + * The first trial just tries to write the page assuming that some  
> other thread
> + * has reset the count for threads inside the enlave by using ETRACK,  
> and
> + * previous thread count has been zeroed out. The second trial calls  
> ETRACK
> + * before EWB. If that fails we kick all the HW threads out, and then  
> do EWB,
> + * which should be guaranteed the succeed.
> + */
> +static void sgx_encl_ewb(struct sgx_epc_page *epc_page,
> +			 struct sgx_backing *backing)
> +{
> +	struct sgx_encl_page *encl_page = epc_page->owner;
> +	struct sgx_encl *encl = encl_page->encl;
> +	struct sgx_va_page *va_page;
> +	unsigned int va_offset;
> +	void *va_slot;
> +	int ret;
> +
> +	encl_page->desc &= ~SGX_ENCL_PAGE_BEING_RECLAIMED;
> +
> +	va_page = list_first_entry(&encl->va_pages, struct sgx_va_page,
> +				   list);
> +	va_offset = sgx_alloc_va_slot(va_page);
> +	va_slot = sgx_get_epc_addr(va_page->epc_page) + va_offset;
> +	if (sgx_va_page_full(va_page))
> +		list_move_tail(&va_page->list, &encl->va_pages);
> +
> +	ret = __sgx_encl_ewb(epc_page, va_slot, backing);
> +	if (ret == SGX_NOT_TRACKED) {
> +		ret = __etrack(sgx_get_epc_addr(encl->secs.epc_page));
> +		if (ret) {
> +			if (encls_failed(ret))
> +				ENCLS_WARN(ret, "ETRACK");
> +		}
> +
> +		ret = __sgx_encl_ewb(epc_page, va_slot, backing);
> +		if (ret == SGX_NOT_TRACKED) {
> +			/*
> +			 * Slow path, send IPIs to kick cpus out of the
> +			 * enclave.  Note, it's imperative that the cpu
> +			 * mask is generated *after* ETRACK, else we'll
> +			 * miss cpus that entered the enclave between
> +			 * generating the mask and incrementing epoch.
> +			 */
> +			on_each_cpu_mask(sgx_encl_ewb_cpumask(encl),
> +					 sgx_ipi_cb, NULL, 1);
> +			ret = __sgx_encl_ewb(epc_page, va_slot, backing);
> +		}
> +	}
> +
> +	if (ret) {
> +		if (encls_failed(ret))
> +			ENCLS_WARN(ret, "EWB");
> +
> +		sgx_free_va_slot(va_page, va_offset);
> +	} else {
> +		encl_page->desc |= va_offset;
> +		encl_page->va_page = va_page;
> +	}
> +}
> +
> +static void sgx_reclaimer_write(struct sgx_epc_page *epc_page,
> +				struct sgx_backing *backing)
> +{
> +	struct sgx_encl_page *encl_page = epc_page->owner;
> +	struct sgx_encl *encl = encl_page->encl;
> +	struct sgx_backing secs_backing;
> +	int ret;
> +
> +	mutex_lock(&encl->lock);
> +
> +	if (atomic_read(&encl->flags) & SGX_ENCL_DEAD) {
> +		ret = __eremove(sgx_get_epc_addr(epc_page));
> +		ENCLS_WARN(ret, "EREMOVE");
> +	} else {
> +		sgx_encl_ewb(epc_page, backing);
> +	}
> +
> +	encl_page->epc_page = NULL;
> +	encl->secs_child_cnt--;
> +
> +	if (!encl->secs_child_cnt) {
> +		if (atomic_read(&encl->flags) & SGX_ENCL_DEAD) {
> +			sgx_free_epc_page(encl->secs.epc_page);
> +			encl->secs.epc_page = NULL;
> +		} else if (atomic_read(&encl->flags) & SGX_ENCL_INITIALIZED) {
> +			ret = sgx_encl_get_backing(encl, PFN_DOWN(encl->size),
> +						   &secs_backing);
> +			if (ret)
> +				goto out;
> +
> +			sgx_encl_ewb(encl->secs.epc_page, &secs_backing);
> +
> +			sgx_free_epc_page(encl->secs.epc_page);
> +			encl->secs.epc_page = NULL;
> +
> +			sgx_encl_put_backing(&secs_backing, true);
> +		}
> +	}
> +
> +out:
> +	mutex_unlock(&encl->lock);
> +}
> +
> +/*
> + * Take a fixed number of pages from the head of the active page pool  
> and
> + * reclaim them to the enclave's private shmem files. Skip the pages,  
> which have
> + * been accessed since the last scan. Move those pages to the tail of  
> active
> + * page pool so that the pages get scanned in LRU like fashion.
> + *
> + * Batch process a chunk of pages (at the moment 16) in order to  
> degrade amount
> + * of IPI's and ETRACK's potentially required. sgx_encl_ewb() does  
> degrade a bit
> + * among the HW threads with three stage EWB pipeline (EWB, ETRACK +  
> EWB and IPI
> + * + EWB) but not sufficiently. Reclaiming one page at a time would  
> also be
> + * problematic as it would increase the lock contention too much, which  
> would
> + * halt forward progress.
> + */
> +static void sgx_reclaim_pages(void)
> +{
> +	struct sgx_epc_page *chunk[SGX_NR_TO_SCAN];
> +	struct sgx_backing backing[SGX_NR_TO_SCAN];
> +	struct sgx_epc_section *section;
> +	struct sgx_encl_page *encl_page;
> +	struct sgx_epc_page *epc_page;
> +	int cnt = 0;
> +	int ret;
> +	int i;
> +
> +	spin_lock(&sgx_active_page_list_lock);
> +	for (i = 0; i < SGX_NR_TO_SCAN; i++) {
> +		if (list_empty(&sgx_active_page_list))
> +			break;
> +
> +		epc_page = list_first_entry(&sgx_active_page_list,
> +					    struct sgx_epc_page, list);
> +		list_del_init(&epc_page->list);
> +		encl_page = epc_page->owner;
> +
> +		if (kref_get_unless_zero(&encl_page->encl->refcount) != 0)
> +			chunk[cnt++] = epc_page;
> +		else
> +			/* The owner is freeing the page. No need to add the
> +			 * page back to the list of reclaimable pages.
> +			 */
> +			epc_page->desc &= ~SGX_EPC_PAGE_RECLAIMABLE;
> +	}
> +	spin_unlock(&sgx_active_page_list_lock);
> +
> +	for (i = 0; i < cnt; i++) {
> +		epc_page = chunk[i];
> +		encl_page = epc_page->owner;
> +
> +		if (!sgx_reclaimer_age(epc_page))
> +			goto skip;
> +
> +		ret = sgx_encl_get_backing(encl_page->encl,
> +					   SGX_ENCL_PAGE_INDEX(encl_page),
> +					   &backing[i]);
> +		if (ret)
> +			goto skip;
> +
> +		mutex_lock(&encl_page->encl->lock);
> +		encl_page->desc |= SGX_ENCL_PAGE_BEING_RECLAIMED;
> +		mutex_unlock(&encl_page->encl->lock);
> +		continue;
> +
> +skip:
> +		spin_lock(&sgx_active_page_list_lock);
> +		list_add_tail(&epc_page->list, &sgx_active_page_list);
> +		spin_unlock(&sgx_active_page_list_lock);
> +
> +		kref_put(&encl_page->encl->refcount, sgx_encl_release);
> +
> +		chunk[i] = NULL;
> +	}
> +
> +	for (i = 0; i < cnt; i++) {
> +		epc_page = chunk[i];
> +		if (epc_page)
> +			sgx_reclaimer_block(epc_page);
> +	}
> +
> +	for (i = 0; i < cnt; i++) {
> +		epc_page = chunk[i];
> +		if (!epc_page)
> +			continue;
> +
> +		encl_page = epc_page->owner;
> +		sgx_reclaimer_write(epc_page, &backing[i]);
> +		sgx_encl_put_backing(&backing[i], true);
> +
> +		kref_put(&encl_page->encl->refcount, sgx_encl_release);
> +		epc_page->desc &= ~SGX_EPC_PAGE_RECLAIMABLE;
> +
> +		section = sgx_get_epc_section(epc_page);
> +		spin_lock(&section->lock);
> +		list_add_tail(&epc_page->list, &section->page_list);
> +		section->free_cnt++;
> +		spin_unlock(&section->lock);
> +	}
> +}
> +
> static void sgx_sanitize_section(struct sgx_epc_section *section)
>  {
> @@ -44,6 +433,23 @@ static void sgx_sanitize_section(struct  
> sgx_epc_section *section)
>  	}
>  }
> +static unsigned long sgx_nr_free_pages(void)
> +{
> +	unsigned long cnt = 0;
> +	int i;
> +
> +	for (i = 0; i < sgx_nr_epc_sections; i++)
> +		cnt += sgx_epc_sections[i].free_cnt;
> +
> +	return cnt;
> +}
> +
> +static bool sgx_should_reclaim(unsigned long watermark)
> +{
> +	return sgx_nr_free_pages() < watermark &&
> +	       !list_empty(&sgx_active_page_list);
> +}
> +
>  static int ksgxswapd(void *p)
>  {
>  	int i;
> @@ -69,6 +475,20 @@ static int ksgxswapd(void *p)
>  			WARN(1, "EPC section %d has unsanitized pages.\n", i);
>  	}
> +	while (!kthread_should_stop()) {
> +		if (try_to_freeze())
> +			continue;
> +
> +		wait_event_freezable(ksgxswapd_waitq,
> +				     kthread_should_stop() ||
> +				     sgx_should_reclaim(SGX_NR_HIGH_PAGES));
> +
> +		if (sgx_should_reclaim(SGX_NR_HIGH_PAGES))
> +			sgx_reclaim_pages();
> +
> +		cond_resched();
> +	}
> +
>  	return 0;
>  }
> @@ -94,6 +514,7 @@ static struct sgx_epc_page  
> *__sgx_alloc_epc_page_from_section(struct sgx_epc_sec
> 	page = list_first_entry(&section->page_list, struct sgx_epc_page, list);
>  	list_del_init(&page->list);
> +	section->free_cnt--;
> 	return page;
>  }
> @@ -127,6 +548,57 @@ struct sgx_epc_page *__sgx_alloc_epc_page(void)
>  	return ERR_PTR(-ENOMEM);
>  }
> +/**
> + * sgx_alloc_epc_page() - Allocate an EPC page
> + * @owner:	the owner of the EPC page
> + * @reclaim:	reclaim pages if necessary
> + *
> + * Iterate through EPC sections and borrow a free EPC page to the  
> caller. When a
> + * page is no longer needed it must be released with  
> sgx_free_epc_page(). If
> + * @reclaim is set to true, directly reclaim pages when we are out of  
> pages. No
> + * mm's can be locked when @reclaim is set to true.
> + *
> + * Finally, wake up ksgxswapd when the number of pages goes below the  
> watermark
> + * before returning back to the caller.
> + *
> + * Return:
> + *   an EPC page,
> + *   -errno on error
> + */
> +struct sgx_epc_page *sgx_alloc_epc_page(void *owner, bool reclaim)
> +{
> +	struct sgx_epc_page *entry;
> +
> +	for ( ; ; ) {
> +		entry = __sgx_alloc_epc_page();
> +		if (!IS_ERR(entry)) {
> +			entry->owner = owner;
> +			break;
> +		}
> +
> +		if (list_empty(&sgx_active_page_list))
> +			return ERR_PTR(-ENOMEM);
> +
> +		if (!reclaim) {
> +			entry = ERR_PTR(-EBUSY);
> +			break;
> +		}
> +
> +		if (signal_pending(current)) {
> +			entry = ERR_PTR(-ERESTARTSYS);
> +			break;
> +		}
> +
> +		sgx_reclaim_pages();
> +		schedule();
> +	}
> +
> +	if (sgx_should_reclaim(SGX_NR_LOW_PAGES))
> +		wake_up(&ksgxswapd_waitq);
> +
> +	return entry;
> +}
> +
>  /**
>   * sgx_free_epc_page() - Free an EPC page
>   * @page:	an EPC page
> @@ -138,12 +610,20 @@ void sgx_free_epc_page(struct sgx_epc_page *page)
>  	struct sgx_epc_section *section = sgx_get_epc_section(page);
>  	int ret;
> +	/*
> +	 * Don't take sgx_active_page_list_lock when asserting the page isn't
> +	 * reclaimable, missing a WARN in the very rare case is preferable to
> +	 * unnecessarily taking a global lock in the common case.
> +	 */
> +	WARN_ON_ONCE(page->desc & SGX_EPC_PAGE_RECLAIMABLE);
> +
>  	ret = __eremove(sgx_get_epc_addr(page));
>  	if (WARN_ONCE(ret, "EREMOVE returned %d (0x%x)", ret, ret))
>  		return;
> 	spin_lock(&section->lock);
>  	list_add_tail(&page->list, &section->page_list);
> +	section->free_cnt++;
>  	spin_unlock(&section->lock);
>  }
> @@ -194,6 +674,7 @@ static bool __init sgx_setup_epc_section(u64 addr,  
> u64 size,
>  		list_add_tail(&page->list, &section->unsanitized_page_list);
>  	}
> +	section->free_cnt = nr_pages;
>  	return true;
> err_out:
> diff --git a/arch/x86/kernel/cpu/sgx/sgx.h  
> b/arch/x86/kernel/cpu/sgx/sgx.h
> index 8d126070db1e..ec4f7b338dbe 100644
> --- a/arch/x86/kernel/cpu/sgx/sgx.h
> +++ b/arch/x86/kernel/cpu/sgx/sgx.h
> @@ -15,6 +15,7 @@
> struct sgx_epc_page {
>  	unsigned long desc;
> +	struct sgx_encl_page *owner;
>  	struct list_head list;
>  };
> @@ -27,6 +28,7 @@ struct sgx_epc_page {
>  struct sgx_epc_section {
>  	unsigned long pa;
>  	void *va;
> +	unsigned long free_cnt;
>  	struct list_head page_list;
>  	struct list_head unsanitized_page_list;
>  	spinlock_t lock;
> @@ -35,6 +37,10 @@ struct sgx_epc_section {
>  #define SGX_EPC_SECTION_MASK		GENMASK(7, 0)
>  #define SGX_MAX_EPC_SECTIONS		(SGX_EPC_SECTION_MASK + 1)
>  #define SGX_MAX_ADD_PAGES_LENGTH	0x100000
> +#define SGX_EPC_PAGE_RECLAIMABLE	BIT(8)
> +#define SGX_NR_TO_SCAN			16
> +#define SGX_NR_LOW_PAGES		32
> +#define SGX_NR_HIGH_PAGES		64
> extern struct sgx_epc_section sgx_epc_sections[SGX_MAX_EPC_SECTIONS];
> @@ -50,7 +56,10 @@ static inline void *sgx_get_epc_addr(struct  
> sgx_epc_page *page)
>  	return section->va + (page->desc & PAGE_MASK) - section->pa;
>  }
> +void sgx_mark_page_reclaimable(struct sgx_epc_page *page);
> +int sgx_unmark_page_reclaimable(struct sgx_epc_page *page);
>  struct sgx_epc_page *__sgx_alloc_epc_page(void);
> +struct sgx_epc_page *sgx_alloc_epc_page(void *owner, bool reclaim);
>  void sgx_free_epc_page(struct sgx_epc_page *page);
> #endif /* _X86_SGX_H */


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