From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 2B4626FB88; Thu, 1 Feb 2024 17:38:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706809136; cv=none; b=hPr1b6Nbmg16yTLAvC4i4/CnnPPS1Cx4DhhtpcTMbAsVlz6aFQBhmLzUsx2Amv2/vGz47kzSiICPWP9YdGKUVvO/ZcXzgD45F2fzgQRu0HujJVtq8b1zuQbBza5JodlA3E52nC1M/Z/yfHHtS2AkFHUcL60CbLUldwo/zTXVq8Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706809136; c=relaxed/simple; bh=+jscayz1j5iTQ/gLXe+z+HvDEvJcz5+9nneP6cJ+HKk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=E1Oy54BLboD4+svxMA0HRo41tJ+2bcrddkoFADgqFDbHUU9IMwqoOxBzB8XccNQrhMK2fPukgZFprHGGr8nucHvaMzSTZqE3vJcZZ909Zyt9TD/4PZP6bdtBI/70ea3rkwmTNB3YCDoFwrTJm1ZJiJ9Zw5XjffuJO6ItZC22Hps= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 32134DA7; Thu, 1 Feb 2024 09:39:36 -0800 (PST) Received: from raptor (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 95BF13F738; Thu, 1 Feb 2024 09:38:48 -0800 (PST) Date: Thu, 1 Feb 2024 17:38:42 +0000 From: Alexandru Elisei To: Anshuman Khandual Cc: catalin.marinas@arm.com, will@kernel.org, oliver.upton@linux.dev, maz@kernel.org, james.morse@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, arnd@arndb.de, akpm@linux-foundation.org, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, mhiramat@kernel.org, rppt@kernel.org, hughd@google.com, pcc@google.com, steven.price@arm.com, vincenzo.frascino@arm.com, david@redhat.com, eugenis@google.com, kcc@google.com, hyesoo.yu@samsung.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kvmarm@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH RFC v3 31/35] khugepaged: arm64: Don't collapse MTE enabled VMAs Message-ID: References: <20240125164256.4147-1-alexandru.elisei@arm.com> <20240125164256.4147-32-alexandru.elisei@arm.com> <599769c3-0aef-4c5b-ac98-f109649862f7@arm.com> Precedence: bulk X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <599769c3-0aef-4c5b-ac98-f109649862f7@arm.com> On Thu, Feb 01, 2024 at 01:42:08PM +0530, Anshuman Khandual wrote: > > > On 1/25/24 22:12, Alexandru Elisei wrote: > > copy_user_highpage() will do memory allocation if there are saved tags for > > the destination page, and the page is missing tag storage. > > > > After commit a349d72fd9ef ("mm/pgtable: add rcu_read_lock() and > > rcu_read_unlock()s"), collapse_huge_page() calls > > __collapse_huge_page_copy() -> .. -> copy_user_highpage() with the RCU lock > > held, which means that copy_user_highpage() can only allocate memory using > > GFP_ATOMIC or equivalent. > > > > Get around this by refusing to collapse pages into a transparent huge page > > if the VMA is MTE-enabled. > > Makes sense when copy_user_highpage() will allocate memory for tag storage. > > > > > Signed-off-by: Alexandru Elisei > > --- > > > > Changes since rfc v2: > > > > * New patch. I think an agreement on whether copy*_user_highpage() should be > > always allowed to sleep, or should not be allowed, would be useful. > > This is a good question ! Even after preventing the collapse of MTE VMA here, > there still might be more paths where a sleeping (i.e memory allocating) > copy*_user_highpage() becomes problematic ? Exactly! > > > > > arch/arm64/include/asm/pgtable.h | 3 +++ > > arch/arm64/kernel/mte_tag_storage.c | 5 +++++ > > include/linux/khugepaged.h | 5 +++++ > > mm/khugepaged.c | 4 ++++ > > 4 files changed, 17 insertions(+) > > > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > > index 87ae59436162..d0473538c926 100644 > > --- a/arch/arm64/include/asm/pgtable.h > > +++ b/arch/arm64/include/asm/pgtable.h > > @@ -1120,6 +1120,9 @@ static inline bool arch_alloc_cma(gfp_t gfp_mask) > > return true; > > } > > > > +bool arch_hugepage_vma_revalidate(struct vm_area_struct *vma, unsigned long address); > > +#define arch_hugepage_vma_revalidate arch_hugepage_vma_revalidate > > + > > #endif /* CONFIG_ARM64_MTE_TAG_STORAGE */ > > #endif /* CONFIG_ARM64_MTE */ > > > > diff --git a/arch/arm64/kernel/mte_tag_storage.c b/arch/arm64/kernel/mte_tag_storage.c > > index ac7b9c9c585c..a99959b70573 100644 > > --- a/arch/arm64/kernel/mte_tag_storage.c > > +++ b/arch/arm64/kernel/mte_tag_storage.c > > @@ -636,3 +636,8 @@ void arch_alloc_page(struct page *page, int order, gfp_t gfp) > > if (tag_storage_enabled() && alloc_requires_tag_storage(gfp)) > > reserve_tag_storage(page, order, gfp); > > } > > + > > +bool arch_hugepage_vma_revalidate(struct vm_area_struct *vma, unsigned long address) > > +{ > > + return !(vma->vm_flags & VM_MTE); > > +} > > diff --git a/include/linux/khugepaged.h b/include/linux/khugepaged.h > > index f68865e19b0b..461e4322dff2 100644 > > --- a/include/linux/khugepaged.h > > +++ b/include/linux/khugepaged.h > > @@ -38,6 +38,11 @@ static inline void khugepaged_exit(struct mm_struct *mm) > > if (test_bit(MMF_VM_HUGEPAGE, &mm->flags)) > > __khugepaged_exit(mm); > > } > > + > > +#ifndef arch_hugepage_vma_revalidate > > +#define arch_hugepage_vma_revalidate(vma, address) 1 > > Please replace s/1/true as arch_hugepage_vma_revalidate() returns bool ? Yeah, that's strange, I don't know why I used 1 there. Will change it to true, thanks for spotting it. > > > +#endif > > Right, above construct is much better than __HAVE_ARCH_XXXX based one. Thanks! Alex > > > + > > #else /* CONFIG_TRANSPARENT_HUGEPAGE */ > > static inline void khugepaged_fork(struct mm_struct *mm, struct mm_struct *oldmm) > > { > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > > index 2b219acb528e..cb9a9ddb4d86 100644 > > --- a/mm/khugepaged.c > > +++ b/mm/khugepaged.c > > @@ -935,6 +935,10 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address, > > */ > > if (expect_anon && (!(*vmap)->anon_vma || !vma_is_anonymous(*vmap))) > > return SCAN_PAGE_ANON; > > + > > + if (!arch_hugepage_vma_revalidate(vma, address)) > > + return SCAN_VMA_CHECK; > > + > > return SCAN_SUCCEED; > > } > > > > Otherwise this LGTM.