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b=KlIpfN7x0gpYPoR9+bN/kCSh/rh0uUpndP1K5upedsbukXV7kqdxpk3rC/GckJwq9 s0z6MQGXfwxzwUE/RP6kRQMiOd3OiJSLSW+MOKGbjH5z24dwkXcSG6vmwQ7cXI/2vw EcqBQTXbacVpnvhLo8TmyCxkRAXOlilLFofG4KaMmyagcKKgL4Nj4lV6EZ2fJTtgSR 6Q3AhLG81CP1AhvIaQX0CKG82Oj+sCp/50qj6EoGKuNekmfA/y03Eti2w4V7S6NgkO TcT9KZJ5Z3AhBHIWzvgUQFr6xnNqNRft5FXal6zcIcqEU1dv2I6rWRrHnS6GTPfHm5 z7v5HH/Xqo7hA== Message-ID: Date: Wed, 5 Aug 2026 10:58:43 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 0/5] Only free healthy pages in high-order has_hwpoisoned folio Content-Language: en-US To: "David Hildenbrand (Arm)" , William Roche , Jiaqi Yan , linmiaohe@huawei.com, ljs@kernel.org, ziy@nvidia.com Cc: osalvador@kernel.org, harry.yoo@oracle.com, willy@infradead.org, osalvador@suse.de, jackmanb@google.com, hannes@cmpxchg.org, nao.horiguchi@gmail.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, rppt@kernel.org, shuah@kernel.org, surenb@google.com, mhocko@suse.com, boudewijn@delta-utec.com References: <20260705180714.3708947-1-jiaqiyan@google.com> <85cb7ea8-8116-4092-8310-69b61eb8602c@kernel.org> <1dea7b3c-7740-474d-b9d4-cd2baf47f181@kernel.org> <168ad406-f6b5-4623-adac-9f894e410e48@kernel.org> <8f787434-5326-4a8f-92d0-467e817a23b4@kernel.org> <8e48c288-2183-4d58-b69d-5f78344b5da5@kernel.org> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 494D7140002 X-Stat-Signature: px4owq8gj3esnmarp6cmjitteih64xn3 X-Rspam-User: X-HE-Tag: 1785920332-82517 X-HE-Meta: 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 g+WsEtr6 Yz60IUlWkbxeXVWBnq6B6kIx8oJMa8pHSZ4E6vp4KO3Q7B81IgvfgDkmua9ekCf7C7G4N2S/KlmWNu1+pmOk4orbzse3bV4SSyKqZ5SPPaAe+5NaeZzIt/o0Fbm6eZ9b6FqryJ9pgXZal2OUdxzyZpn1jGCs1/ypMjrPSN8ySKehmAiwxwG/SRBg1sD33UhNskAIX1Nkxxx4rDh2dnRHbWM5Bjef/ltD9ZaV6N1KyS+shbNSSANqJOz1BJJO4JH4v1gj7bLa7iYSnkVckDIJE5gLx4THqHQzhUrYrQzh3Gdz+YhT419LNwaFpSmBE1KZbk04sOHcIJ1rY36adu6A0Ez9T9xr3B97lhKl/5vbFzBUHwxErPlgTo7oA31k07U9m76sVzrYHFXLDegbaI83udwT9n2HXEVPZpvMkogBmJhP4L8c= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/4/26 21:51, David Hildenbrand (Arm) wrote: > On 7/28/26 19:18, Vlastimil Babka (SUSE) wrote: >> On 7/27/26 16:20, David Hildenbrand (Arm) wrote: >>> On 7/22/26 10:27, Vlastimil Babka (SUSE) wrote: >>>> >>>> Would it truly fix the issue, or rather there would still be a race window >>>> left where we check that there's no hwpoison flag in the re-enabled check, >>>> and only then someone sets it? >>> >>> Why are we checking PageHWPoison at all then in check_new_page()? >> >> We check all kinds of unexpected state, when that's enable. PageHWPoison >> could have been considered unexpected too, when the checks were made more >> and more optional (first by Mel and then me). >> >> But indeed it seems the PageHWPoison check is supposed to be load-bearing >> (hi, Lorenzo!). It's intentionally handled before bad_page() (with a taint) >> in check_new_page_bad(). Commits 2a7684a23e9c and f4c18e6f7b5b are also a hint. >> >>> I think we created a mess. >> >> Yes, the PageHWPoison handling was made part of debugging sanity check and >> then not recognized properly as load-bearing later. > > BTW, I'd assume we can check for PageHWPoison at free time fairly efficiently, as we > touch all page flags already. > > Something along the lines of: > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 520ebd2fa40b5..57f89f8684168 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1321,6 +1321,7 @@ 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); > + unsigned int hwpoisoned = 0; > > if (fpi_flags & FPI_PREPARED) > return true; > @@ -1347,21 +1348,6 @@ static __always_inline bool __free_pages_prepare(struct page *page, > count_vm_events(UNEVICTABLE_PGCLEARED, nr_pages); > } > > - if (unlikely(PageHWPoison(page)) && !order) { > - /* Do not let hwpoison pages hit pcplists/buddy */ > - reset_page_owner(page, order); > - page_table_check_free(page, order); > - pgalloc_tag_sub(page, 1 << order); > - > - /* > - * The page is isolated and accounted for. > - * Mark the codetag as empty to avoid accounting error > - * when the page is freed by unpoison_memory(). > - */ > - clear_page_tag_ref(page); > - return false; > - } > - > VM_BUG_ON_PAGE(compound && compound_order(page) != order, page); > > /* > @@ -1395,8 +1381,26 @@ static __always_inline bool __free_pages_prepare(struct page *page, > } > } > tail_page->flags.f &= ~PAGE_FLAGS_CHECK_AT_PREP; > + hwpoisoned += PageHWPoison(tail_page); > } > } > + hwpoisoned += PageHWPoison(page); > + > + if (unlikely(hwpoisoned)) { > + /* Do not let hwpoison pages hit pcplists/buddy */ > + reset_page_owner(page, order); > + page_table_check_free(page, order); > + pgalloc_tag_sub(page, 1 << order); > + > + /* > + * The page is isolated and accounted for. > + * Mark the codetag as empty to avoid accounting error > + * when the page is freed by unpoison_memory(). > + */ > + clear_page_tag_ref(page); > + return false; > + } > + > if (folio_test_anon(folio)) { > mod_mthp_stat(order, MTHP_STAT_NR_ANON, -1); > folio->mapping = NULL; > diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile > > > Of course, we could also fallback for order>0 to do some smart splitting. I think the freeing part is relatively fine, as tackled by this series. > Checking on allocation efficiently is indeed a bit more tricky. For compound > pages prep_compound_page() will already walk all pages. Yeah and non-compound high-order pages should just go away eventually, so I wouldn't worry about making them slower now. But it's tricky because prep_compound_page() happens later when we don't expect anything to fail anymore, so it would take some refactoring. > Having hwpoison logic to just sync with the buddy when setting hwpoison flags > would be nicer. I suggested that (soft-offline does it). There might be some downsides, but I can't judge how much they would manifest in practice: https://lore.kernel.org/all/CACw3F50nVECJ%2Bk4g%3DQVZ80yzi_awCOcUiCuB0CYcUfxND9-7Tw@mail.gmail.com/ > Then we could (maybe) have the rule that no hwpoisoned page can enter the buddy, and no > page can become hwpoisoned while in the buddy. Consequently, no hwpoisoned page can > leave the buddy (except weird races while allocating, but then it's just an allocated > page). I'd love if that approach was feasible, yeah. > Maybe. >