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Date:   Mon, 27 Jun 2022 19:17:09 -0700
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Subject: Re: [PATCH 2/4] kvm: Merge "atomic" and "write" in
 __gfn_to_pfn_memslot()
Content-Language: en-US
To:     Peter Xu <peterx@redhat.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        David Hildenbrand <david@redhat.com>,
        "Dr . David Alan Gilbert" <dgilbert@redhat.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Linux MM Mailing List <linux-mm@kvack.org>,
        Sean Christopherson <seanjc@google.com>
References: <20220622213656.81546-1-peterx@redhat.com>
 <20220622213656.81546-3-peterx@redhat.com>
From:   John Hubbard <jhubbard@nvidia.com>
In-Reply-To: <20220622213656.81546-3-peterx@redhat.com>
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On 6/22/22 14:36, Peter Xu wrote:
> Merge two boolean parameters into a bitmask flag called kvm_gtp_flag_t for
> __gfn_to_pfn_memslot().  This cleans the parameter lists, and also prepare
> for new boolean to be added to __gfn_to_pfn_memslot().
> 
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>   arch/arm64/kvm/mmu.c                   |  5 ++--
>   arch/powerpc/kvm/book3s_64_mmu_hv.c    |  5 ++--
>   arch/powerpc/kvm/book3s_64_mmu_radix.c |  5 ++--
>   arch/x86/kvm/mmu/mmu.c                 | 10 +++----
>   include/linux/kvm_host.h               |  9 ++++++-
>   virt/kvm/kvm_main.c                    | 37 +++++++++++++++-----------
>   virt/kvm/kvm_mm.h                      |  6 +++--
>   virt/kvm/pfncache.c                    |  2 +-
>   8 files changed, 49 insertions(+), 30 deletions(-)
> 
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index f5651a05b6a8..ce1edb512b4e 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -1204,8 +1204,9 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>   	 */
>   	smp_rmb();
>   
> -	pfn = __gfn_to_pfn_memslot(memslot, gfn, false, NULL,
> -				   write_fault, &writable, NULL);
> +	pfn = __gfn_to_pfn_memslot(memslot, gfn,
> +				   write_fault ? KVM_GTP_WRITE : 0,
> +				   NULL, &writable, NULL);
>   	if (pfn == KVM_PFN_ERR_HWPOISON) {
>   		kvm_send_hwpoison_signal(hva, vma_shift);
>   		return 0;
> diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> index 514fd45c1994..e2769d58dd87 100644
> --- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
> +++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> @@ -598,8 +598,9 @@ int kvmppc_book3s_hv_page_fault(struct kvm_vcpu *vcpu,
>   		write_ok = true;
>   	} else {
>   		/* Call KVM generic code to do the slow-path check */
> -		pfn = __gfn_to_pfn_memslot(memslot, gfn, false, NULL,
> -					   writing, &write_ok, NULL);
> +		pfn = __gfn_to_pfn_memslot(memslot, gfn,
> +					   writing ? KVM_GTP_WRITE : 0,
> +					   NULL, &write_ok, NULL);
>   		if (is_error_noslot_pfn(pfn))
>   			return -EFAULT;
>   		page = NULL;
> diff --git a/arch/powerpc/kvm/book3s_64_mmu_radix.c b/arch/powerpc/kvm/book3s_64_mmu_radix.c
> index 42851c32ff3b..232b17c75b83 100644
> --- a/arch/powerpc/kvm/book3s_64_mmu_radix.c
> +++ b/arch/powerpc/kvm/book3s_64_mmu_radix.c
> @@ -845,8 +845,9 @@ int kvmppc_book3s_instantiate_page(struct kvm_vcpu *vcpu,
>   		unsigned long pfn;
>   
>   		/* Call KVM generic code to do the slow-path check */
> -		pfn = __gfn_to_pfn_memslot(memslot, gfn, false, NULL,
> -					   writing, upgrade_p, NULL);
> +		pfn = __gfn_to_pfn_memslot(memslot, gfn,
> +					   writing ? KVM_GTP_WRITE : 0,
> +					   NULL, upgrade_p, NULL);
>   		if (is_error_noslot_pfn(pfn))
>   			return -EFAULT;
>   		page = NULL;
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index f4653688fa6d..e92f1ab63d6a 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -3968,6 +3968,7 @@ void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu, struct kvm_async_pf *work)
>   
>   static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
>   {
> +	kvm_gtp_flag_t flags = fault->write ? KVM_GTP_WRITE : 0;
>   	struct kvm_memory_slot *slot = fault->slot;
>   	bool async;
>   
> @@ -3999,8 +4000,8 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
>   	}
>   
>   	async = false;
> -	fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, false, &async,
> -					  fault->write, &fault->map_writable,
> +	fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, flags,
> +					  &async, &fault->map_writable,
>   					  &fault->hva);
>   	if (!async)
>   		return RET_PF_CONTINUE; /* *pfn has correct page already */
> @@ -4016,9 +4017,8 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
>   		}
>   	}
>   
> -	fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, false, NULL,
> -					  fault->write, &fault->map_writable,
> -					  &fault->hva);
> +	fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, flags, NULL,
> +					  &fault->map_writable, &fault->hva);

The flags arg does improve the situation, yes.

>   	return RET_PF_CONTINUE;
>   }
>   
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index c20f2d55840c..b646b6fcaec6 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -1146,8 +1146,15 @@ kvm_pfn_t gfn_to_pfn_prot(struct kvm *kvm, gfn_t gfn, bool write_fault,
>   		      bool *writable);
>   kvm_pfn_t gfn_to_pfn_memslot(const struct kvm_memory_slot *slot, gfn_t gfn);
>   kvm_pfn_t gfn_to_pfn_memslot_atomic(const struct kvm_memory_slot *slot, gfn_t gfn);
> +
> +/* gfn_to_pfn (gtp) flags */
> +typedef unsigned int __bitwise kvm_gtp_flag_t;

A minor naming problem: GTP and especially gtp_flags is way too close
to gfp_flags. It will make people either wonder if it's a typo, or
worse, *assume* that it's a typo. :)

Yes, "read the code", but if you can come up with a better TLA than GTP
here, let's consider using it.

Overall, the change looks like an improvement, even though

     write_fault ? KVM_GTP_WRITE : 0

is not wonderful. But improving *that* leads to a a big pile of diffs
that are rather beyond the scope here.


thanks,
-- 
John Hubbard
NVIDIA


> +
> +#define  KVM_GTP_WRITE          ((__force kvm_gtp_flag_t) BIT(0))
> +#define  KVM_GTP_ATOMIC         ((__force kvm_gtp_flag_t) BIT(1))
> +
>   kvm_pfn_t __gfn_to_pfn_memslot(const struct kvm_memory_slot *slot, gfn_t gfn,
> -			       bool atomic, bool *async, bool write_fault,
> +			       kvm_gtp_flag_t gtp_flags, bool *async,
>   			       bool *writable, hva_t *hva);
>   
>   void kvm_release_pfn_clean(kvm_pfn_t pfn);
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 64ec2222a196..952400b42ee9 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2444,9 +2444,11 @@ static bool hva_to_pfn_fast(unsigned long addr, bool write_fault,
>    * The slow path to get the pfn of the specified host virtual address,
>    * 1 indicates success, -errno is returned if error is detected.
>    */
> -static int hva_to_pfn_slow(unsigned long addr, bool *async, bool write_fault,
> +static int hva_to_pfn_slow(unsigned long addr, bool *async,
> +			   kvm_gtp_flag_t gtp_flags,
>   			   bool *writable, kvm_pfn_t *pfn)
>   {
> +	bool write_fault = gtp_flags & KVM_GTP_WRITE;
>   	unsigned int flags = FOLL_HWPOISON;
>   	struct page *page;
>   	int npages = 0;
> @@ -2565,20 +2567,22 @@ static int hva_to_pfn_remapped(struct vm_area_struct *vma,
>   /*
>    * Pin guest page in memory and return its pfn.
>    * @addr: host virtual address which maps memory to the guest
> - * @atomic: whether this function can sleep
> + * @gtp_flags: kvm_gtp_flag_t flags (atomic, write, ..)
>    * @async: whether this function need to wait IO complete if the
>    *         host page is not in the memory
> - * @write_fault: whether we should get a writable host page
>    * @writable: whether it allows to map a writable host page for !@write_fault
>    *
> - * The function will map a writable host page for these two cases:
> + * The function will map a writable (KVM_GTP_WRITE set) host page for these
> + * two cases:
>    * 1): @write_fault = true
>    * 2): @write_fault = false && @writable, @writable will tell the caller
>    *     whether the mapping is writable.
>    */
> -kvm_pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool *async,
> -		     bool write_fault, bool *writable)
> +kvm_pfn_t hva_to_pfn(unsigned long addr, kvm_gtp_flag_t gtp_flags, bool *async,
> +		     bool *writable)
>   {
> +	bool write_fault = gtp_flags & KVM_GTP_WRITE;
> +	bool atomic = gtp_flags & KVM_GTP_ATOMIC;
>   	struct vm_area_struct *vma;
>   	kvm_pfn_t pfn = 0;
>   	int npages, r;
> @@ -2592,7 +2596,7 @@ kvm_pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool *async,
>   	if (atomic)
>   		return KVM_PFN_ERR_FAULT;
>   
> -	npages = hva_to_pfn_slow(addr, async, write_fault, writable, &pfn);
> +	npages = hva_to_pfn_slow(addr, async, gtp_flags, writable, &pfn);
>   	if (npages == 1)
>   		return pfn;
>   
> @@ -2625,10 +2629,11 @@ kvm_pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool *async,
>   }
>   
>   kvm_pfn_t __gfn_to_pfn_memslot(const struct kvm_memory_slot *slot, gfn_t gfn,
> -			       bool atomic, bool *async, bool write_fault,
> +			       kvm_gtp_flag_t gtp_flags, bool *async,
>   			       bool *writable, hva_t *hva)
>   {
> -	unsigned long addr = __gfn_to_hva_many(slot, gfn, NULL, write_fault);
> +	unsigned long addr = __gfn_to_hva_many(slot, gfn, NULL,
> +					       gtp_flags & KVM_GTP_WRITE);
>   
>   	if (hva)
>   		*hva = addr;
> @@ -2651,28 +2656,30 @@ kvm_pfn_t __gfn_to_pfn_memslot(const struct kvm_memory_slot *slot, gfn_t gfn,
>   		writable = NULL;
>   	}
>   
> -	return hva_to_pfn(addr, atomic, async, write_fault,
> -			  writable);
> +	return hva_to_pfn(addr, gtp_flags, async, writable);
>   }
>   EXPORT_SYMBOL_GPL(__gfn_to_pfn_memslot);
>   
>   kvm_pfn_t gfn_to_pfn_prot(struct kvm *kvm, gfn_t gfn, bool write_fault,
>   		      bool *writable)
>   {
> -	return __gfn_to_pfn_memslot(gfn_to_memslot(kvm, gfn), gfn, false, NULL,
> -				    write_fault, writable, NULL);
> +	return __gfn_to_pfn_memslot(gfn_to_memslot(kvm, gfn), gfn,
> +				    write_fault ? KVM_GTP_WRITE : 0,
> +				    NULL, writable, NULL);
>   }
>   EXPORT_SYMBOL_GPL(gfn_to_pfn_prot);
>   
>   kvm_pfn_t gfn_to_pfn_memslot(const struct kvm_memory_slot *slot, gfn_t gfn)
>   {
> -	return __gfn_to_pfn_memslot(slot, gfn, false, NULL, true, NULL, NULL);
> +	return __gfn_to_pfn_memslot(slot, gfn, KVM_GTP_WRITE,
> +				    NULL, NULL, NULL);
>   }
>   EXPORT_SYMBOL_GPL(gfn_to_pfn_memslot);
>   
>   kvm_pfn_t gfn_to_pfn_memslot_atomic(const struct kvm_memory_slot *slot, gfn_t gfn)
>   {
> -	return __gfn_to_pfn_memslot(slot, gfn, true, NULL, true, NULL, NULL);
> +	return __gfn_to_pfn_memslot(slot, gfn, KVM_GTP_WRITE | KVM_GTP_ATOMIC,
> +				    NULL, NULL, NULL);
>   }
>   EXPORT_SYMBOL_GPL(gfn_to_pfn_memslot_atomic);
>   
> diff --git a/virt/kvm/kvm_mm.h b/virt/kvm/kvm_mm.h
> index 41da467d99c9..1c870911eb48 100644
> --- a/virt/kvm/kvm_mm.h
> +++ b/virt/kvm/kvm_mm.h
> @@ -3,6 +3,8 @@
>   #ifndef __KVM_MM_H__
>   #define __KVM_MM_H__ 1
>   
> +#include <linux/kvm_host.h>
> +
>   /*
>    * Architectures can choose whether to use an rwlock or spinlock
>    * for the mmu_lock.  These macros, for use in common code
> @@ -24,8 +26,8 @@
>   #define KVM_MMU_READ_UNLOCK(kvm)	spin_unlock(&(kvm)->mmu_lock)
>   #endif /* KVM_HAVE_MMU_RWLOCK */
>   
> -kvm_pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool *async,
> -		     bool write_fault, bool *writable);
> +kvm_pfn_t hva_to_pfn(unsigned long addr, kvm_gtp_flag_t gtp_flags, bool *async,
> +		     bool *writable);
>   
>   #ifdef CONFIG_HAVE_KVM_PFNCACHE
>   void gfn_to_pfn_cache_invalidate_start(struct kvm *kvm,
> diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c
> index dd84676615f1..0f9f6b5d2fbb 100644
> --- a/virt/kvm/pfncache.c
> +++ b/virt/kvm/pfncache.c
> @@ -123,7 +123,7 @@ static kvm_pfn_t hva_to_pfn_retry(struct kvm *kvm, unsigned long uhva)
>   		smp_rmb();
>   
>   		/* We always request a writeable mapping */
> -		new_pfn = hva_to_pfn(uhva, false, NULL, true, NULL);
> +		new_pfn = hva_to_pfn(uhva, KVM_GTP_WRITE, NULL, NULL);
>   		if (is_error_noslot_pfn(new_pfn))
>   			break;
>