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[2003:d8:2f0c:c200:fa4a:c4ff:1b32:21ce]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-426ce5cfe69sm37683358f8f.32.2025.10.16.13.18.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 16 Oct 2025 13:18:20 -0700 (PDT) Message-ID: <91dbea57-d5b0-49b7-8920-3a2d252c46b0@redhat.com> Date: Thu, 16 Oct 2025 22:18:17 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH RESEND 1/3] mm: memory_failure: Fix MF_DELAYED handling on truncation during failure To: Lisa Wang , linmiaohe@huawei.com, nao.horiguchi@gmail.com, akpm@linux-foundation.org, pbonzini@redhat.com, shuah@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org Cc: rientjes@google.com, seanjc@google.com, ackerleytng@google.com, vannapurve@google.com, michael.roth@amd.com, jiaqiyan@google.com, tabba@google.com, dave.hansen@linux.intel.com References: <57ed0bcbcfcec6fda89d60727467d7bd621c95ab.1760551864.git.wyihan@google.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: ksa6ucofntr47pwudekha7jsoxmk9gke X-Rspamd-Queue-Id: 90BDD180010 X-Rspamd-Server: rspam09 X-HE-Tag: 1760645905-167534 X-HE-Meta: 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 oODAToVe 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 15.10.25 20:58, Lisa Wang wrote: > The .error_remove_folio a_ops is used by different filesystems to handle > folio truncation upon discovery of a memory failure in the memory > associated with the given folio. > > Currently, MF_DELAYED is treated as an error, causing "Failed to punch > page" to be written to the console. MF_DELAYED is then relayed to the > caller of truncat_error_folio() as MF_FAILED. This further causes > memory_failure() to return -EBUSY, which then always causes a SIGBUS. > > This is also implies that regardless of whether the thread's memory > corruption kill policy is PR_MCE_KILL_EARLY or PR_MCE_KILL_LATE, a > memory failure within guest_memfd memory will always cause a SIGBUS. > > Update truncate_error_folio() to return MF_DELAYED to the caller if the > .error_remove_folio() callback reports MF_DELAYED. > > Generalize the comment: MF_DELAYED means memory failure was handled and > some other part of memory failure will be handled later (e.g. a next > access will result in the process being killed). Specifically for > guest_memfd, a next access by the guest will result in an error returned > to the userspace VMM. > > With delayed handling, the filemap continues to hold refcounts on the > folio. Hence, take that into account when checking for extra refcounts > in me_pagecache_clean(). This is aligned with the implementation in > me_swapcache_dirty(), where, if a folio is still in the swap cache, > extra_pins is set to true. > > Signed-off-by: Lisa Wang > --- > mm/memory-failure.c | 24 +++++++++++++++--------- > 1 file changed, 15 insertions(+), 9 deletions(-) > > diff --git a/mm/memory-failure.c b/mm/memory-failure.c > index df6ee59527dd..77f665c16a73 100644 > --- a/mm/memory-failure.c > +++ b/mm/memory-failure.c > @@ -922,9 +922,11 @@ static int kill_accessing_process(struct task_struct *p, unsigned long pfn, > * by the m-f() handler immediately. > * > * MF_DELAYED - The m-f() handler marks the page as PG_hwpoisoned'ed. > - * The page is unmapped, and is removed from the LRU or file mapping. > - * An attempt to access the page again will trigger page fault and the > - * PF handler will kill the process. > + * It means memory_failure was handled (e.g. removed from file mapping or the > + * LRU) and some other part of memory failure will be handled later (e.g. a > + * next access will result in the process being killed). Specifically for > + * guest_memfd, a next access by the guest will result in an error returned to > + * the userspace VMM. > * > * MF_RECOVERED - The m-f() handler marks the page as PG_hwpoisoned'ed. > * The page has been completely isolated, that is, unmapped, taken out of > @@ -999,6 +1001,9 @@ static int truncate_error_folio(struct folio *folio, unsigned long pfn, > if (mapping->a_ops->error_remove_folio) { > int err = mapping->a_ops->error_remove_folio(mapping, folio); > > + if (err == MF_DELAYED) > + return err; > + > if (err != 0) > pr_info("%#lx: Failed to punch page: %d\n", pfn, err); > else if (!filemap_release_folio(folio, GFP_NOIO)) > @@ -1108,18 +1113,19 @@ static int me_pagecache_clean(struct page_state *ps, struct page *p) > goto out; > } > > - /* > - * The shmem page is kept in page cache instead of truncating > - * so is expected to have an extra refcount after error-handling. > - */ > - extra_pins = shmem_mapping(mapping); > - > /* > * Truncation is a bit tricky. Enable it per file system for now. > * > * Open: to take i_rwsem or not for this? Right now we don't. > */ > ret = truncate_error_folio(folio, page_to_pfn(p), mapping); > + > + /* > + * The shmem page, or any page with MF_DELAYED error handling, is kept in > + * page cache instead of truncating, so is expected to have an extra > + * refcount after error-handling. > + */ > + extra_pins = shmem_mapping(mapping) || ret == MF_DELAYED; Well, to do it cleanly shouldn't we let shmem_error_remove_folio() also return MF_DELAYED and remove this shmem special case? Or is there a good reason shmem_mapping() wants to return 0 -- and maybe guest_memfd would also wan to do that? Just reading the code here the inconsistency is unclear. -- Cheers David / dhildenb