From nobody Mon Feb 9 10:26:34 2026 Received: from out-183.mta1.migadu.com (out-183.mta1.migadu.com [95.215.58.183]) (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 7E88B17E for ; Mon, 27 Jan 2025 19:53:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.183 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738007626; cv=none; b=nT9Q6HdXDxvU40nzDEBwA2+Z4229EIVJC2ITRhyZq7G+mAFrEE9K0Wr2V7nln8EhknMZwYj+QEi6UZdJ2tzymBgaCQRBv1nXsnwnyK2290wIFfkCz5LOOPwBxF5J3N+rwZaSekwbjMtStB3Qq/7eYmBiLABE5Rtl903GaV7e/W8= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738007626; c=relaxed/simple; bh=nqnISomD/j61bQat1/AeepObcUfncv3ETHk5z0QUqBg=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=tHUConYLZUDUJD2Gq3rUxdAZuUqpy5buckOB3pXxaDZkvHeWCoxRLcHAu1C096xwrjx0U323N7OW0Tf3VmkXFzsf1IOFHT4K3EOJWb5D4VFf7Wyg0m0u63xGrsNQVPFLLZFnaB2E5Tct6/o0dWWPB0r8KHFVk8ZRueNim/drRRQ= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=NM7kH1sr; arc=none smtp.client-ip=95.215.58.183 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="NM7kH1sr" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1738007612; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=nnkGNTLvskPKX+krc93edAVPeknd45rshqikoa8lHn8=; b=NM7kH1srmRC0B+tepoX5im3jW2S5lwyzfg758+BMaz1YAFAkNNcYth3KzC8HKS4gkXvBie llSsflYW+S9Hhvdnag0ml7w2S30g63kqz4L7nUaVTgDbCFf2orRTm3vPMzSbL3TY6Cq12f g0AcwLNaxn6ME9Zo7kYZ+6sq+3HZArI= From: Roman Gushchin To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Andrew Morton , Roman Gushchin , Jann Horn , Peter Zijlstra , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Hugh Dickins , linux-arch@vger.kernel.org Subject: [PATCH v4] mmu_gather: move tlb flush for VM_PFNMAP/VM_MIXEDMAP vmas into free_pgtables() Date: Mon, 27 Jan 2025 19:53:21 +0000 Message-ID: <20250127195321.35779-1-roman.gushchin@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Migadu-Flow: FLOW_OUT Content-Type: text/plain; charset="utf-8" Commit b67fbebd4cf9 ("mmu_gather: Force tlb-flush VM_PFNMAP vmas") added a forced tlbflush to tlb_vma_end(), which is required to avoid a race between munmap() and unmap_mapping_range(). However it added some overhead to other paths where tlb_vma_end() is used, but vmas are not removed, e.g. madvise(MADV_DONTNEED). Fix this by moving the tlb flush out of tlb_end_vma() into free_pgtables(), somewhat similar to the stable version of the original commit: e.g. stable commit 895428ee124a ("mm: Force TLB flush for PFNMAP mappings before unlink_file_vma()"). Note, that if tlb->fullmm is set, no flush is required, as the whole mm is about to be destroyed. Signed-off-by: Roman Gushchin Cc: Jann Horn Cc: Peter Zijlstra Cc: Will Deacon Cc: "Aneesh Kumar K.V" Cc: Andrew Morton Cc: Nick Piggin Cc: Hugh Dickins Cc: linux-arch@vger.kernel.org Cc: linux-mm@kvack.org --- v4: - naming/comments update (by Peter Z.) - check vma->vma->vm_flags in tlb_free_vma() (by Peter Z.) v3: - added initialization of vma_pfn in __tlb_reset_range() (by Hugh D.) v2: - moved vma_pfn flag handling into tlb.h (by Peter Z.) - added comments (by Peter Z.) - fixed the vma_pfn flag setting (by Hugh D.) --- include/asm-generic/tlb.h | 49 +++++++++++++++++++++++++++++++-------- mm/memory.c | 2 ++ 2 files changed, 41 insertions(+), 10 deletions(-) diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h index e402aef79c93..dd673ec59893 100644 --- a/include/asm-generic/tlb.h +++ b/include/asm-generic/tlb.h @@ -58,6 +58,11 @@ * Defaults to flushing at tlb_end_vma() to reset the range; helps when * there's large holes between the VMAs. * + * - tlb_free_vma() + * + * tlb_free_vma() marks the start of unlinking the vma and freeing + * page-tables. + * * - tlb_remove_table() * * tlb_remove_table() is the basic primitive to free page-table directo= ries @@ -400,7 +405,10 @@ static inline void __tlb_reset_range(struct mmu_gather= *tlb) * Do not reset mmu_gather::vma_* fields here, we do not * call into tlb_start_vma() again to set them if there is an * intermediate flush. + * + * Except for vma_pfn, that only cares if there's pending TLBI. */ + tlb->vma_pfn =3D 0; } =20 #ifdef CONFIG_MMU_GATHER_NO_RANGE @@ -465,7 +473,12 @@ tlb_update_vma_flags(struct mmu_gather *tlb, struct vm= _area_struct *vma) */ tlb->vma_huge =3D is_vm_hugetlb_page(vma); tlb->vma_exec =3D !!(vma->vm_flags & VM_EXEC); - tlb->vma_pfn =3D !!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)); + + /* + * Track if there's at least one VM_PFNMAP/VM_MIXEDMAP vma + * in the tracked range, see tlb_free_vma(). + */ + tlb->vma_pfn |=3D !!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)); } =20 static inline void tlb_flush_mmu_tlbonly(struct mmu_gather *tlb) @@ -564,23 +577,39 @@ static inline void tlb_start_vma(struct mmu_gather *t= lb, struct vm_area_struct * } =20 static inline void tlb_end_vma(struct mmu_gather *tlb, struct vm_area_stru= ct *vma) +{ + if (tlb->fullmm || IS_ENABLED(CONFIG_MMU_GATHER_MERGE_VMAS)) + return; + + /* + * Do a TLB flush and reset the range at VMA boundaries; this avoids + * the ranges growing with the unused space between consecutive VMAs, + * but also the mmu_gather::vma_* flags from tlb_start_vma() rely on + * this. + */ + tlb_flush_mmu_tlbonly(tlb); +} + +static inline void tlb_free_vma(struct mmu_gather *tlb, struct vm_area_str= uct *vma) { if (tlb->fullmm) return; =20 /* * VM_PFNMAP is more fragile because the core mm will not track the - * page mapcount -- there might not be page-frames for these PFNs after - * all. Force flush TLBs for such ranges to avoid munmap() vs - * unmap_mapping_range() races. + * page mapcount -- there might not be page-frames for these PFNs + * after all. + * + * Specifically() there is a race between munmap() and + * unmap_mapping_range(), where munmap() will unlink the VMA, such + * that unmap_mapping_range() will no longer observe the VMA and + * no-op, without observing the TLBI, returning prematurely. + * + * So if we're about to unlink such a VMA, and we have pending + * TLBI for such a vma, flush things now. */ - if (tlb->vma_pfn || !IS_ENABLED(CONFIG_MMU_GATHER_MERGE_VMAS)) { - /* - * Do a TLB flush and reset the range at VMA boundaries; this avoids - * the ranges growing with the unused space between consecutive VMAs. - */ + if ((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) && tlb->vma_pfn) tlb_flush_mmu_tlbonly(tlb); - } } =20 /* diff --git a/mm/memory.c b/mm/memory.c index 539c0f7c6d54..4ea5e286c68f 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -378,6 +378,7 @@ void free_pgtables(struct mmu_gather *tlb, struct ma_st= ate *mas, if (unlikely(xa_is_zero(next))) next =3D NULL; =20 + tlb_free_vma(tlb, vma); /* * Hide vma from rmap and truncate_pagecache before freeing * pgtables @@ -403,6 +404,7 @@ void free_pgtables(struct mmu_gather *tlb, struct ma_st= ate *mas, next =3D mas_find(mas, ceiling - 1); if (unlikely(xa_is_zero(next))) next =3D NULL; + tlb_free_vma(tlb, vma); if (mm_wr_locked) vma_start_write(vma); unlink_anon_vmas(vma); --=20 2.48.1.262.g85cc9f2d1e-goog