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Message-ID: <0fedf6f3-3ab3-e1d2-fd6e-3dbe8e92f06d@redhat.com>
Date:   Fri, 10 Jun 2022 14:12:00 +0200
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Subject: Re: [PATCH v3 1/1] mm/memory-failure: don't allow to unpoison hw
 corrupted page
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To:     zhenwei pi <pizhenwei@bytedance.com>, naoya.horiguchi@nec.com,
        akpm@linux-foundation.org
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org
References: <20220610114646.162764-1-pizhenwei@bytedance.com>
 <20220610114646.162764-2-pizhenwei@bytedance.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
In-Reply-To: <20220610114646.162764-2-pizhenwei@bytedance.com>
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On 10.06.22 13:46, 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>
> Cc: David Hildenbrand <david@redhat.com>
> Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
> ---
>  mm/memory-failure.c | 59 +++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 59 insertions(+)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index b85661cbdc4a..3124f428302c 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -2068,6 +2068,58 @@ static int __init memory_failure_init(void)
>  }
>  core_initcall(memory_failure_init);
>  
> +/*
> + * Unpoisoning a hardware corrupted page with *NOT PRESENT* KPTE leads panic.
> + * Test a page is valid in the kernel mapping.
> + */
> +static bool kmap_valid(struct page *page)
> +{
> +	unsigned long addr = (unsigned long)page_to_virt(page);
> +	pgd_t *pgd;
> +	p4d_t *p4d;
> +	pud_t *pud;
> +	pmd_t *pmd;
> +	pte_t *pte;
> +
> +	pgd = pgd_offset_k(addr);
> +	if (pgd_none(*pgd))
> +		return false;
> +	if (pgd_leaf(*pgd))
> +		return true;
> +	if (pgd_bad(*pgd))
> +		return false;
> +
> +	p4d = p4d_offset(pgd, addr);
> +	if (p4d_none(*p4d))
> +		return false;
> +	if (p4d_leaf(*p4d))
> +		return true;
> +	if (p4d_bad(*p4d))
> +		return false;
> +
> +	pud = pud_offset(p4d, addr);
> +	if (pud_none(*pud))
> +		return false;
> +	if (pud_leaf(*pud))
> +		return true;
> +	if (pud_bad(*pud))
> +		return false;
> +
> +	pmd = pmd_offset(pud, addr);
> +	if (pmd_none(*pmd))
> +		return false;
> +	if (pmd_leaf(*pmd))
> +		return true;
> +	if (pmd_bad(*pmd))
> +		return false;
> +
> +	pte = pte_offset_map(pmd, addr);
> +	if (pte_none(*pte) || !pte_present(*pte))
> +		return false;
> +
> +	return true;
> +}
> +
>  #define unpoison_pr_info(fmt, pfn, rs)			\
>  ({							\
>  	if (__ratelimit(rs))				\
> @@ -2109,6 +2161,13 @@ int unpoison_memory(unsigned long pfn)
>  		goto unlock_mutex;
>  	}
>  
> +	if (!kmap_valid(page)) {
> +		unpoison_pr_info("Unpoison: Page was hardware poisoned %#lx\n",
> +				 pfn, &unpoison_rs);
> +		ret = -EOPNOTSUPP;
> +		goto unlock_mutex;
> +	}
> +
>  	if (page_count(page) > 1) {
>  		unpoison_pr_info("Unpoison: Someone grabs the hwpoison page %#lx\n",
>  				 pfn, &unpoison_rs);

I really prefer just disabling the unpoisioning mechanism in case there
is a real hw injected error.

-- 
Thanks,

David / dhildenb