Re: Re: [PATCH v5 1/1] mm/memory-failure: disable unpoison once hw error happens

[zhenwei pi]

On 6/15/22 12:23, Oscar Salvador wrote:
> On Wed, Jun 15, 2022 at 10:00:05AM +0800, 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.
> >
> > Suggested by David&Naoya, disable unpoison mechanism when a real HW error
> > happens 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@xxxxxxx>
> > Cc: David Hildenbrand <david@xxxxxxxxxx>
> > Signed-off-by: zhenwei pi <pizhenwei@xxxxxxxxxxxxx>
> > ---
> ...
> ...
> > diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> > index b85661cbdc4a..385b5e99bfc1 100644
> > --- a/mm/memory-failure.c
> > +++ b/mm/memory-failure.c
> > @@ -69,6 +69,8 @@ int sysctl_memory_failure_recovery __read_mostly = 1;
> >   
> >   atomic_long_t num_poisoned_pages __read_mostly = ATOMIC_LONG_INIT(0);
> >   
> > +static bool hw_memory_failure;
> > +
> >   static bool __page_handle_poison(struct page *page)
> >   {
> >   	int ret;
> > @@ -1768,6 +1770,9 @@ int memory_failure(unsigned long pfn, int flags)
> >   
> >   	mutex_lock(&mf_mutex);
> >   
> > +	if (!(flags & MF_SW_SIMULATED))
> > +		hw_memory_failure = true;
> > +
> >   	p = pfn_to_online_page(pfn);
> >   	if (!p) {
> >   		res = arch_memory_failure(pfn, flags);
> > @@ -2103,6 +2108,13 @@ int unpoison_memory(unsigned long pfn)
> >   
> >   	mutex_lock(&mf_mutex);
> >   
> > +	if (hw_memory_failure) {
> > +		unpoison_pr_info("Unpoison: Disabled after HW memory failure %#lx\n",
> > +				 pfn, &unpoison_rs);
> > +		ret = -EOPNOTSUPP;
> > +		goto unlock_mutex;
> > +	}
>
> If we disable this, I would move this at the beginning of the function.
> We do not really care whether the pfn is valid or getting the head of
> the page, etc.
> So, unless I'm missing something, this should be enough?

Hi,

Because memory_failure() may be called by hardware error randomly, 
hw_memory_failure should be protected by mf_mutex to avoid this case:
int unpoison_memory(unsigned long pfn)
{
    ...
    if (hw_memory_failure) {
    }
    ... --> memory_failure() happens, and mark hw_memory_failure as true
    mutex_lock(&mf_mutex);
}

> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 385b5e99bfc1..ece15f07dee7 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -2100,6 +2100,12 @@ int unpoison_memory(unsigned long pfn)
>          static DEFINE_RATELIMIT_STATE(unpoison_rs, DEFAULT_RATELIMIT_INTERVAL,
>                                          DEFAULT_RATELIMIT_BURST);
>   
> +       if (hw_memory_failure) {
> +                unpoison_pr_info("Unpoison: Disabled after HW memory failure\n",
> +                                 &unpoison_rs);
> +               ret -EOPNOTSUPP;
> +        }
> +
>          if (!pfn_valid(pfn))
>                  return -ENXIO;
>   

--
zhenwei pi