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Message-ID: <260b719b-9138-9615-fae4-b5b4c86674a2@redhat.com>
Date:   Wed, 8 Jun 2022 11:30:18 +0200
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Subject: Re: [PATCH v2 1/1] mm/memory-failure: don't allow to unpoison hw
 corrupted page
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To:     zhenwei pi <pizhenwei@bytedance.com>, akpm@linux-foundation.org,
        naoya.horiguchi@nec.com
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org
References: <20220608084356.40894-1-pizhenwei@bytedance.com>
 <20220608084356.40894-2-pizhenwei@bytedance.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
In-Reply-To: <20220608084356.40894-2-pizhenwei@bytedance.com>
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On 08.06.22 10:43, zhenwei pi wrote:
> Currently unpoison_memory(unsigned long pfn) is designed for soft
> poison(hwpoison-inject) only. Since 17fae1294ad9d, the KPTE gets
> cleared on a x86 platform once hardware memory corrupts.
> 
> Unpoisoning a hardware corrupted page puts page back buddy only,
> the kernel has a chance to access the page with *NOT PRESENT* KPTE.
> This leads BUG during accessing on the corrupted KPTE.
> 
> Do not allow to unpoison hardware corrupted page in unpoison_memory() to
> avoid BUG like this:
> 
>  Unpoison: Software-unpoisoned page 0x61234
>  BUG: unable to handle page fault for address: ffff888061234000
>  #PF: supervisor write access in kernel mode
>  #PF: error_code(0x0002) - not-present page
>  PGD 2c01067 P4D 2c01067 PUD 107267063 PMD 10382b063 PTE 800fffff9edcb062
>  Oops: 0002 [#1] PREEMPT SMP NOPTI
>  CPU: 4 PID: 26551 Comm: stress Kdump: loaded Tainted: G   M       OE     5.18.0.bm.1-amd64 #7
>  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996) ...
>  RIP: 0010:clear_page_erms+0x7/0x10
>  Code: ...
>  RSP: 0000:ffffc90001107bc8 EFLAGS: 00010246
>  RAX: 0000000000000000 RBX: 0000000000000901 RCX: 0000000000001000
>  RDX: ffffea0001848d00 RSI: ffffea0001848d40 RDI: ffff888061234000
>  RBP: ffffea0001848d00 R08: 0000000000000901 R09: 0000000000001276
>  R10: 0000000000000003 R11: 0000000000000000 R12: 0000000000000001
>  R13: 0000000000000000 R14: 0000000000140dca R15: 0000000000000001
>  FS:  00007fd8b2333740(0000) GS:ffff88813fd00000(0000) knlGS:0000000000000000
>  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>  CR2: ffff888061234000 CR3: 00000001023d2005 CR4: 0000000000770ee0
>  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>  DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>  PKRU: 55555554
>  Call Trace:
>   <TASK>
>   prep_new_page+0x151/0x170
>   get_page_from_freelist+0xca0/0xe20
>   ? sysvec_apic_timer_interrupt+0xab/0xc0
>   ? asm_sysvec_apic_timer_interrupt+0x1b/0x20
>   __alloc_pages+0x17e/0x340
>   __folio_alloc+0x17/0x40
>   vma_alloc_folio+0x84/0x280
>   __handle_mm_fault+0x8d4/0xeb0
>   handle_mm_fault+0xd5/0x2a0
>   do_user_addr_fault+0x1d0/0x680
>   ? kvm_read_and_reset_apf_flags+0x3b/0x50
>   exc_page_fault+0x78/0x170
>   asm_exc_page_fault+0x27/0x30
> 
> Fixes: 847ce401df392 ("HWPOISON: Add unpoisoning support")
> Fixes: 17fae1294ad9d ("x86/{mce,mm}: Unmap the entire page if the whole page is affected and poisoned")
> Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
> Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
> ---
>  mm/memory-failure.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index b85661cbdc4a..da99a2b7ef35 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -2090,6 +2090,7 @@ int unpoison_memory(unsigned long pfn)
>  {
>  	struct page *page;
>  	struct page *p;
> +	pte_t *kpte;
>  	int ret = -EBUSY;
>  	int freeit = 0;
>  	static DEFINE_RATELIMIT_STATE(unpoison_rs, DEFAULT_RATELIMIT_INTERVAL,
> @@ -2103,6 +2104,14 @@ int unpoison_memory(unsigned long pfn)
>  
>  	mutex_lock(&mf_mutex);
>  
> +	kpte = virt_to_kpte((unsigned long)page_to_virt(p));
> 
I'm curious whether virt_to_kpte is sane to use, especially, when having
the direct map map PMDs and not PTEs?

virt_to_kpte() only checks for pmd_none() -- but what if we have
pmd_large()?

Naive me would assume that calling virt_to_kpte() from generic code is
broken. Only mm/highmem.c uses it, however, 32bit most probably also
doesn't have large mappings in the page tables for the direct map.

-- 
Thanks,

David / dhildenb