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Fri, 18 Aug 2023 14:15:37 -0700 (PDT) Date: Fri, 18 Aug 2023 14:15:32 -0700 Mime-Version: 1.0 X-Mailer: git-send-email 2.42.0.rc1.204.g551eb34607-goog Message-ID: <20230818211533.2523697-1-zokeefe@google.com> Subject: [PATCH v2 1/2] mm/thp: fix "mm: thp: kill __transhuge_page_enabled()" From: "Zach O'Keefe" To: linux-mm@kvack.org, Yang Shi Cc: linux-kernel@vger.kernel.org, "Zach O'Keefe" , Saurabh Singh Sengar X-Rspamd-Queue-Id: 89A27180024 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: f83z5o7u3sm9aez4czmfpxqfgxhdua1c X-HE-Tag: 1692393338-64962 X-HE-Meta: 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 qKmX6WWf 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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: The 6.0 commits: commit 9fec51689ff6 ("mm: thp: kill transparent_hugepage_active()") commit 7da4e2cb8b1f ("mm: thp: kill __transhuge_page_enabled()") merged "can we have THPs in this VMA?" logic that was previously done separately by fault-path, khugepaged, and smaps "THPeligible" checks. During the process, the semantics of the fault path check changed in two ways: 1) A VM_NO_KHUGEPAGED check was introduced (also added to smaps path). 2) We no longer checked if non-anonymous memory had a vm_ops->huge_fault handler that could satisfy the fault. Previously, this check had been done in create_huge_pud() and create_huge_pmd() routines, but after the changes, we never reach those routines. During the review of the above commits, it was determined that in-tree users weren't affected by the change; most notably, since the only relevant user (in terms of THP) of VM_MIXEDMAP or ->huge_fault is DAX, which is explicitly approved early in approval logic. However, there is at least one occurrence where an out-of-tree driver that used VM_HUGEPAGE|VM_MIXEDMAP with a vm_ops->huge_fault handler, was broken. Remove the VM_NO_KHUGEPAGED check when not in collapse path and give any ->huge_fault handler a chance to handle the fault. Note that we don't validate the file mode or mapping alignment, which is consistent with the behavior before the aforementioned commits. Fixes: 7da4e2cb8b1f ("mm: thp: kill __transhuge_page_enabled()") Reported-by: Saurabh Singh Sengar Signed-off-by: Zach O'Keefe Cc: Yang Shi Reviewed-by:Yang Shi . --- Changed from v1[1]: - [Saurabhi] Allow ->huge_fault handler to handle fault, if it exists [1] https://lore.kernel.org/linux-mm/CAAa6QmQw+F=o6htOn=6ADD6mwvMO=Ow_67f3ifBv3GpXx9Xg_g@mail.gmail.com/ --- mm/huge_memory.c | 17 ++++++++++------- 1 file changed, 10 insertions(+), 7 deletions(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index eb3678360b97..cd379b2c077b 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -96,11 +96,11 @@ bool hugepage_vma_check(struct vm_area_struct *vma, unsigned long vm_flags, return in_pf; /* - * Special VMA and hugetlb VMA. + * khugepaged special VMA and hugetlb VMA. * Must be checked after dax since some dax mappings may have * VM_MIXEDMAP set. */ - if (vm_flags & VM_NO_KHUGEPAGED) + if (!in_pf && !smaps && (vm_flags & VM_NO_KHUGEPAGED)) return false; /* @@ -128,12 +128,15 @@ bool hugepage_vma_check(struct vm_area_struct *vma, unsigned long vm_flags, !hugepage_flags_always()))) return false; - /* Only regular file is valid */ - if (!in_pf && file_thp_enabled(vma)) - return true; - if (!vma_is_anonymous(vma)) - return false; + return in_pf ? + /* + * Trust that ->huge_fault() handlers know + * what they are doing in fault path. + */ + !!vma->vm_ops->huge_fault : + /* Only regular file is valid in collapse path */ + file_thp_enabled(vma); if (vma_is_temporary_stack(vma)) return false;