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b=lVWeB8fbPSQmk5ZnZjfxYmqJ5aSP0JS3vYx0Vqq74YYPmMlYbtoJrGFZDnc1/x2LW eWPYxgha49wLuGMjUawePYF21z0O7tARazj+R23XvBeiIxqu5/08V8WNHwlXfIBbW4 Q/Y5ItJaRyFpZCHp/TgKRLWclZCDLA7jknQSUFb0t1x5Vp1w0zC45URa/kOvi+Gtgl VROBoaqKpS67RBMIRO0QJNxVBZdxYHmGF4SUXfmTOHXEQekBj3WKz2HRZra79+AO+5 yIHLpZcxzuFGhCdMLZcj+n3/cUaSRsU/T6I1p5PfHrUeaTAT30hJ246g723Ly2zprh STeJCP5RYZSoQ== Message-ID: Date: Tue, 10 Feb 2026 10:33:06 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: thp: Deny THP for guest_memfd and secretmem in file_thp_enabled() To: Ackerley Tng , Deepanshu Kartikey Cc: akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, seanjc@google.com, pbonzini@redhat.com, michael.roth@amd.com, vannapurve@google.com, ziy@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot+33a04338019ac7e43a44@syzkaller.appspotmail.com References: <20260209033558.22943-1-kartikey406@gmail.com> <0d9cada8-7148-4a5c-a09d-120ef54559d7@kernel.org> <4ed1b111-f2f1-4f89-9308-fdd9d706ca37@kernel.org> <8f188d73-fc97-414b-bdaa-e72032b2bf82@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 4B0B74000C X-Stat-Signature: iiusm45d6gqxkdcr7zx1nmhoyb1imerc X-HE-Tag: 1770715995-644468 X-HE-Meta: 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 HlHg2QPu 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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: >> BUT, something just occurred to me. >> >> We added the mc-handling in >> >> commit 98c76c9f1ef7599b39bfd4bd99b8a760d4a8cd3b >> Author: Jiaqi Yan >> Date: Wed Mar 29 08:11:19 2023 -0700 >> >> mm/khugepaged: recover from poisoned anonymous memory >> >> .. >> >> So I assume kernels before that would crash when collapsing? >> >> Looking at 5.15.199, it does not contain 98c76c9f1e [1]. >> >> So I suspect we need a fix+stable backport. >> >> Who volunteers to try a secretmem reproducer on a stable kernel? :) >> > > I could give this a shot. 5.15.199 doesn't have AS_INACCESSIBLE. Should > we backport AS_INACCESSIBLE there or could the fix for 5.15.199 just be > special-casing secretmem like you suggested below? Yes. If there is no guest_memfd we wouldn't need it. > >> >> The following is a bit nasty as well but should do the trick until we rip >> out the CONFIG_READ_ONLY_THP_FOR_FS stuff. >> >> >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index 03886d4ccecc..4ac1cb36b861 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -40,6 +40,7 @@ >> #include >> #include >> #include >> +#include >> >> #include >> #include "internal.h" >> @@ -94,6 +95,10 @@ static inline bool file_thp_enabled(struct vm_area_struct *vma) >> >> inode = file_inode(vma->vm_file); >> >> + if (mapping_inaccessible(inode->i_mapping) || >> + secretmem_mapping(inode->i_mapping)) >> + return false; >> + > > Regarding the degradation of filesystems that don't support large folios > yet: Do you mean having the collapse function respect AS_FOLIO_ORDER_MAX > would disable collapsing for filesystems that actually want pages to be > collapsed, but don't update max folio order and hence appear to not > support large folios yet? > > What about a check like this instead > > if (!mapping_large_folio_support()) > return false; That would essentially disable CONFIG_READ_ONLY_THP_FOR_FS (support for THP before filesystems started supporting large folios officially), no? -- Cheers, David