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[2003:d8:2f05:e100:526f:9b8:bd2a:2997]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46e32bf61b1sm90731705e9.2.2025.09.29.00.34.13 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 29 Sep 2025 00:34:15 -0700 (PDT) Message-ID: <8ef5e3fd-2ee8-453a-b8ae-584e3d606aa4@redhat.com> Date: Mon, 29 Sep 2025 09:34:12 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/1] mm: prevent poison consumption when splitting THP To: Qiuxu Zhuo , akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, linmiaohe@huawei.com, tony.luck@intel.com Cc: ziy@nvidia.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, nao.horiguchi@gmail.com, farrah.chen@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Zaborowski References: <20250928032842.1399147-1-qiuxu.zhuo@intel.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20250928032842.1399147-1-qiuxu.zhuo@intel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 28.09.25 05:28, Qiuxu Zhuo wrote: > From: Andrew Zaborowski > > When performing memory error injection on a THP (Transparent Huge Page) > mapped to userspace on an x86 server, the kernel panics with the following > trace. The expected behavior is to terminate the affected process instead > of panicking the kernel, as the x86 Machine Check code can recover from an > in-userspace #MC. > > mce: [Hardware Error]: CPU 0: Machine Check Exception: f Bank 3: bd80000000070134 > mce: [Hardware Error]: RIP 10: {memchr_inv+0x4c/0xf0} > mce: [Hardware Error]: TSC afff7bbff88a ADDR 1d301b000 MISC 80 PPIN 1e741e77539027db > mce: [Hardware Error]: PROCESSOR 0:d06d0 TIME 1758093249 SOCKET 0 APIC 0 microcode 80000320 > mce: [Hardware Error]: Run the above through 'mcelog --ascii' > mce: [Hardware Error]: Machine check: Data load in unrecoverable area of kernel > Kernel panic - not syncing: Fatal local machine check > > The root cause of this panic is that handling a memory failure triggered by > an in-userspace #MC necessitates splitting the THP. The splitting process > employs a mechanism, implemented in try_to_map_unused_to_zeropage(), which > reads the sub-pages of the THP to identify zero-filled pages. However, > reading the sub-pages results in a second in-kernel #MC, occurring before > the initial memory_failure() completes, ultimately leading to a kernel > panic. See the kernel panic call trace on the two #MCs. > > First Machine Check occurs // [1] > memory_failure() // [2] > try_to_split_thp_page() > split_huge_page() > split_huge_page_to_list_to_order() > __folio_split() // [3] > remap_page() > remove_migration_ptes() > remove_migration_pte() > try_to_map_unused_to_zeropage() > memchr_inv() // [4] > Second Machine Check occurs // [5] > Kernel panic > > [1] Triggered by accessing a hardware-poisoned THP in userspace, which is > typically recoverable by terminating the affected process. > > [2] Call folio_set_has_hwpoisoned() before try_to_split_thp_page(). > > [3] Pass the RMP_USE_SHARED_ZEROPAGE remap flag to remap_page(). > > [4] Re-access sub-pages of the hw-poisoned THP in the kernel. > > [5] Triggered in-kernel, leading to a panic kernel. > > In Step[2], memory_failure() sets the has_hwpoisoned flag on the THP, > right before calling try_to_split_thp_page(). Fix this panic by not > passing the RMP_USE_SHARED_ZEROPAGE flag to remap_page() in Step[3] > if the THP has the has_hwpoisoned flag set. This prevents access to > sub-pages of the poisoned THP for zero-page identification, avoiding > a second in-kernel #MC that would cause kernel panic. > > [ Qiuxu: Re-worte the commit message. ] > > Reported-by: Farrah Chen > Signed-off-by: Andrew Zaborowski > Tested-by: Farrah Chen > Tested-by: Qiuxu Zhuo > Reviewed-by: Qiuxu Zhuo > Signed-off-by: Qiuxu Zhuo > --- > mm/huge_memory.c | 3 ++- > mm/memory-failure.c | 6 ++++-- > 2 files changed, 6 insertions(+), 3 deletions(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 9c38a95e9f09..1568f0308b90 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -3588,6 +3588,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order, > struct list_head *list, bool uniform_split) > { > struct deferred_split *ds_queue = get_deferred_split_queue(folio); > + bool has_hwpoisoned = folio_test_has_hwpoisoned(folio); > XA_STATE(xas, &folio->mapping->i_pages, folio->index); > struct folio *end_folio = folio_next(folio); > bool is_anon = folio_test_anon(folio); > @@ -3858,7 +3859,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order, > if (nr_shmem_dropped) > shmem_uncharge(mapping->host, nr_shmem_dropped); > > - if (!ret && is_anon) > + if (!ret && is_anon && !has_hwpoisoned) > remap_flags = RMP_USE_SHARED_ZEROPAGE; > remap_page(folio, 1 << order, remap_flags); > > diff --git a/mm/memory-failure.c b/mm/memory-failure.c > index df6ee59527dd..3ba6fd4079ab 100644 > --- a/mm/memory-failure.c > +++ b/mm/memory-failure.c > @@ -2351,8 +2351,10 @@ int memory_failure(unsigned long pfn, int flags) > * otherwise it may race with THP split. > * And the flag can't be set in get_hwpoison_page() since > * it is called by soft offline too and it is just called > - * for !MF_COUNT_INCREASED. So here seems to be the best > - * place. > + * for !MF_COUNT_INCREASED. > + * It also tells split_huge_page() to not bother using > + * the shared zeropage -- the all-zeros check would > + * consume the poison. So here seems to be the best place. > * > * Don't need care about the above error handling paths for > * get_hwpoison_page() since they handle either free page Hm, I wonder if we should actually check in try_to_map_unused_to_zeropage() whether the page has the hwpoison flag set. Nothing wrong with scanning non-affected pages. In thp_underused() we should just skip the folio entirely I guess, so keep it simple. So what about something like this: diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 9c38a95e9f091..d4109fd7fa1f2 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -4121,6 +4121,9 @@ static bool thp_underused(struct folio *folio) if (khugepaged_max_ptes_none == HPAGE_PMD_NR - 1) return false; + folio_contain_hwpoisoned_page(folio) + return false; + for (i = 0; i < folio_nr_pages(folio); i++) { kaddr = kmap_local_folio(folio, i * PAGE_SIZE); if (!memchr_inv(kaddr, 0, PAGE_SIZE)) { diff --git a/mm/migrate.c b/mm/migrate.c index 9e5ef39ce73af..393fc2ffc96e5 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -305,8 +305,9 @@ static bool try_to_map_unused_to_zeropage(struct page_vma_mapped_walk *pvmw, pte_t newpte; void *addr; - if (PageCompound(page)) + if (PageCompound(page) || PageHWPoison(page)) return false; + VM_BUG_ON_PAGE(!PageAnon(page), page); VM_BUG_ON_PAGE(!PageLocked(page), page); VM_BUG_ON_PAGE(pte_present(ptep_get(pvmw->pte)), page); -- Cheers David / dhildenb