From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3BDB038BF72 for ; Mon, 22 Jun 2026 08:30:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782117060; cv=none; b=j9KUQJck96Ke41VxVU3PzQD1JzvBOoO5QffzhuBSvttIBGoe9wbWXBX+SoASR8EF37UpXMkIGcnB66VXDi7Anab5qcZC9TdVxMpWZeUA+SX5aVs1gSudiMdtBP2wXI4RoDGYaITgb5iQuae8/M5GJ31XcyHc7mu38U/X8hX1LzA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782117060; c=relaxed/simple; bh=4G3AXsVW1pejIUPfXZuVUfL5JeEKq2NjHfJyrFeVSiU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=HydEH4azL4l30qgrdUZSgwyW3q9vzqsSfS3DGdpsghBhue7XE8cwIhVqWiKTp2GOh9BgjBYyZ4eROL4PBtAPIXk8CyjI5p/2KX1xq11qkkwtM4thTc1zyUZKBH2gDUHn44eIF/CaZ8BjK4TjXa/3mse62bx00LzME60wiFtic14= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=jUuRGoBq; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="jUuRGoBq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EB3B71F000E9; Mon, 22 Jun 2026 08:30:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782117056; bh=hMhQum2Av1RFbMst+Tl4omq8ZzUVWTZzxalRsQZ2rP8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=jUuRGoBqGCpk6fRGo3soMfzhmQvzF5K2paXg0kxlg0v7MMkc+NCubOXTwcXZ5I9dO M2EqUJic01xFBcIBMnJtxB2eP9J7r5YbSNGlevjq/kZg7d3jAeNR+HcLKSeEvm2blR 3N0z08nJqWIPis48HVXuHvtSPjYENa/4wUZ03R7Rx8rskjliJzCvyruTIgBMGK4seg vuLBqfNqGrQRIxE78F/xPZl1ELOF3o/ENCCowLpYZPKsWs6TvqD75JSnxlayDPIJZ7 /lvf079ShTu4X5yQ3CnkhUPc5/J+j+5VI2Woe/+qD0A2gwkRhgDIaTgZR9iRi6/12r a94VJq6nhkxZg== Message-ID: Date: Mon, 22 Jun 2026 10:30:49 +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 v5 1/4] mm/page_alloc: only free healthy pages in high-order has_hwpoisoned folio Content-Language: en-US To: Jiaqi Yan Cc: osalvador@suse.de, Miaohe Lin , lorenzo.stoakes@oracle.com, jackmanb@google.com, hannes@cmpxchg.org, nao.horiguchi@gmail.com, david@kernel.org, william.roche@oracle.com, tony.luck@intel.com, wangkefeng.wang@huawei.com, jane.chu@oracle.com, akpm@linux-foundation.org, muchun.song@linux.dev, liam@infradead.org, rientjes@google.com, duenwen@google.com, jthoughton@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, vbabka@suse.cz, rppt@kernel.org, shuah@kernel.org, surenb@google.com, mhocko@suse.com, boudewijn@delta-utec.com, ljs@kernel.org, osalvador@kernel.org, willy@infradead.org, Zi Yan , harry.yoo@oracle.com References: <20260531055829.3636554-1-jiaqiyan@google.com> <20260531055829.3636554-2-jiaqiyan@google.com> <84a0b176-8534-e03a-9e6e-400c74ddab0b@huawei.com> <45290F97-B8BD-4A9B-934E-0A122A5F3A80@nvidia.com> <5942d4d2-5719-4196-af49-b35cf5f7b88d@kernel.org> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 6/22/26 03:12, Jiaqi Yan wrote: > On Thu, Jun 18, 2026 at 8:02 AM Vlastimil Babka (SUSE) > wrote: >> >> On 6/16/26 08:53, Miaohe Lin wrote: >> > On 2026/6/16 11:23, Jiaqi Yan wrote: >> >> On Fri, Jun 12, 2026 at 11:34 AM Zi Yan wrote: >> >>> >> >>> On 8 Jun 2026, at 23:44, Miaohe Lin wrote: >> >>> >> >>>> On 2026/5/31 13:58, Jiaqi Yan wrote: >> >>>>> At the end of dissolve_free_hugetlb_folio(), a free HugeTLB folio >> >>>>> becomes non-HugeTLB, and it is released to buddy allocator >> >>>>> as a high-order folio, e.g. a folio that contains 262144 pages >> >>>>> if the folio was a 1G HugeTLB hugepage. >> >>>>> >> >>>>> This is problematic if the HugeTLB hugepage contained HWPoison >> >>>>> subpages. In that case, since buddy allocator does not check >> >>>>> HWPoison for non-zero-order folio, the raw HWPoison page can >> >>>>> be given out with its buddy page and be re-used by either >> >>>>> kernel or userspace. >> >>>>> >> >>>>> Memory failure recovery (MFR) in kernel does attempt to take >> >>>>> raw HWPoison page off buddy allocator after >> >>>>> dissolve_free_hugetlb_folio(). However, there is always a time >> >>>>> window between dissolve_free_hugetlb_folio() frees a HWPoison >> >>>>> high-order folio to buddy allocator and MFR takes HWPoison >> >>>>> raw page off buddy allocator. >> >>>>> >> >>>>> Another similar situation is when a transparent huge page (THP) >> >>>>> runs into memory failure but splitting failed. Such THP will >> >>>>> eventually be released to buddy allocator when owning userspace >> >>>>> processes are gone, but with certain subpages having HWPoison. >> >>>>> >> >>>>> One obvious way to avoid both problems is to add page sanity >> >>>>> checks in page allocate or free path. However, it is against >> >>>>> the past efforts to reduce sanity check overhead [1,2,3]. >> >>>>> >> >>>>> Introduce free_has_hwpoisoned() to only free the healthy pages >> >>>>> and to exclude the HWPoison ones in the high-order folio. >> >>>>> The idea is to iterate through the sub-pages of the folio to >> >>>>> identify contiguous ranges of healthy pages. >> >>>>> >> >>>>> free_has_hwpoisoned() is added in free_pages_prepare() as >> >>>>> a shortcut and is only invoked if PG_has_hwpoisoned indicates >> >>>>> HWPoison page exists and after checks and preparations in >> >>>>> free_pages_prepare() all succeeded. free_has_hwpoisoned() then >> >>>>> can re-use free_prepared_contig_range() [4] to decompose healthy >> >>>>> ranges into the largest possible chunks of different orders. >> >>>>> Every chunk meets the requirements to be freed via free_one_page(). >> >>>>> >> >>>>> free_has_hwpoisoned() has linear time complexity wrt the number >> >>>>> of pages in the folio. While the power-of-two decomposition >> >>>>> ensures that the number of calls to the buddy allocator is >> >>>>> logarithmic for each contiguous healthy range, the mandatory >> >>>>> linear scan of pages to identify PageHWPoison() defines the >> >>>>> overall time complexity. For a 1G hugepage having 8 HWPoison >> >>>>> pages, free_has_hwpoisoned() takes around 1ms on average on >> >>>>> a system having 56 Intel Skylake physical cores. This is >> >>>>> 15x to the case of freeing no HWPoison page. The cost is far >> >>>>> from triggering soft lockup, and fair for handling exceptional >> >>>>> hardware memory errors. >> >>>>> >> >>>>> [1] https://lore.kernel.org/linux-mm/1460711275-1130-15-git-send-email-mgorman@techsingularity.net >> >>>>> [2] https://lore.kernel.org/linux-mm/1460711275-1130-16-git-send-email-mgorman@techsingularity.net >> >>>>> [3] https://lore.kernel.org/all/20230216095131.17336-1-vbabka@suse.cz >> >>>>> [4] https://lore.kernel.org/all/20260401101634.2868165-2-usama.anjum@arm.com >> >>>>> >> >>>>> Signed-off-by: Jiaqi Yan >> >>>> >> >>>> Thanks for your update. This patch looks good to me while some comments below. >> >>>> >> >>>>> --- >> >>>>> mm/page_alloc.c | 85 +++++++++++++++++++++++++++++++++++++++++++++++++ >> >>>>> 1 file changed, 85 insertions(+) >> >>>>> >> >>>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> >>>>> index e47679e7a9db..03df929abca6 100644 >> >>>>> --- a/mm/page_alloc.c >> >>>>> +++ b/mm/page_alloc.c >> >>>>> @@ -208,6 +208,7 @@ gfp_t gfp_allowed_mask __read_mostly = GFP_BOOT_MASK; >> >>>>> unsigned int pageblock_order __read_mostly; >> >>>>> #endif >> >>>>> >> >>>>> +static void free_has_hwpoisoned(struct page *page, unsigned int order); >> >>>>> static void __free_pages_ok(struct page *page, unsigned int order, >> >>>>> fpi_t fpi_flags); >> >>>>> static void reserve_highatomic_pageblock(struct page *page, int order, >> >>>>> @@ -1309,6 +1310,14 @@ static inline void pgalloc_tag_sub_pages(struct alloc_tag *tag, unsigned int nr) >> >>>>> >> >>>>> #endif /* CONFIG_MEM_ALLOC_PROFILING */ >> >>>>> >> >>>>> +/* >> >>>>> + * Returns >> >>>>> + * - true: checks and preparations all good, caller can proceed freeing. >> >>>>> + * - false: do not proceed freeing for one of the following reasons: >> >>>>> + * 1. Some check failed so it is not safe to proceed freeing. >> >>>>> + * 2. A compound page has some HWPoison pages. The healthy pages >> >>>>> + * are already safely freed, and the HWPoison ones isolated. >> >>>>> + */ >> >>>>> static __always_inline bool __free_pages_prepare(struct page *page, >> >>>>> unsigned int order, fpi_t fpi_flags) >> >>>>> { >> >>>>> @@ -1317,6 +1326,15 @@ static __always_inline bool __free_pages_prepare(struct page *page, >> >>>>> bool init = want_init_on_free(); >> >>>>> bool compound = PageCompound(page); >> >>>>> struct folio *folio = page_folio(page); >> >>>>> + /* >> >>>>> + * When dealing with compound page, PG_has_hwpoisoned is cleared >> >>>>> + * with PAGE_FLAGS_SECOND. So the check must be done first. >> >>>>> + * >> >>>>> + * Note we can't exclude PG_has_hwpoisoned from PAGE_FLAGS_SECOND. >> >>>>> + * Because PG_has_hwpoisoned == PG_active, free_page_is_bad() will >> >>>>> + * confuse and complaint that the first tail page is still active. >> >>>>> + */ >> >>>>> + bool should_fhh = compound && folio_test_has_hwpoisoned(folio); >> >>>>> >> >>>>> if (fpi_flags & FPI_PREPARED) >> >>>>> return true; >> >>>>> @@ -1443,6 +1461,16 @@ static __always_inline bool __free_pages_prepare(struct page *page, >> >>>>> >> >>>>> debug_pagealloc_unmap_pages(page, 1 << order); >> >>>>> >> >>>>> + /* >> >>>>> + * After breaking down compound page and dealing with page metadata >> >>>>> + * (e.g. page owner and page alloc tags), take a shortcut if this >> >>>>> + * was a compound page containing certain HWPoison subpages. >> >>>>> + */ >> >>>>> + if (should_fhh) { >> >>>>> + free_has_hwpoisoned(page, order); >> >>>>> + return false; >> >>>>> + } >> >>>> >> >>>> When the code reaches here, the hwpoisoned pages have passed through kernel_poison_pages, >> >>>> kasan_poison_pages, kernel_init_pages, arch_free_page... These functions might write to >> >>>> the hwpoisoned pages. Is it safe to do so? >> >>> >> >>> At least, kernel_poison_pages() writes to the page. It probably should be >> >>> moved up, somewhere like above kernel_poison_pages(). >> >> >> >> Writing to HWPoison pages (location having memory error) is usually >> >> safe, as in it doesn't cause a machine check exception. Memory >> > >> > In x86, set_mce_nospec is called for hwpoisoned pages. So writing to >> > HWPoison pages would cause unexpected page fault in kernel? >> > >> > Thanks. >> >> Seems we'll have to extract everything between kernel_poison_pages() and >> debug_pagealloc_unmap_pages() to a function, don't call it when should_fhh >> is true and instead call it in free_has_hwpoisoned() on pages that are not >> HWPoison? I think it's acceptable to do it there one page at a time in order > > Let's say I extract everything between kernel_poison_pages() and > debug_pagealloc_unmap_pages() into __free_pages_sanitize(page, order). > How about adding an extra bool to let __free_prepared_contig_range() > to do __free_pages_sanitize() for a block of pages? Sure, let's see how it will look like. > This doesn't really matter to kernel_poison_pages() and > clear_highpages_kasan_tagged() because they deal with pages one by > one. However, it seems more efficient for kasan_poison() and > debug_pagealloc_unmap_pages(). > > BTW, I wonder whether I should carry over the fpi_t flags from > __free_pages_prepare() into free_has_hwpoisoned() and > __free_prepared_contig_range()? Right now the intended code paths to > get to __free_pages_prepare() all just have FPI_NONE, e.g. > free_frozen_pages() and free_unref_folios(). So I didn't complicate > things further. If it helps, why not. Maybe have a new fpi_t flag instead of a new bool then? >> not to complicate things as most of that stuff is debug-only and we're >> handling a rare event.