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 835BFDF4D for ; Mon, 15 Apr 2024 08:59:20 +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=1713171562; cv=none; b=oRMYukScO3kYqlvmhJ2B+tw8X8RMhUepLVFJunkIlAsyMz0zwEpHs2eSV6TpfuA+h1mr++RCshtQGN6ZOe9ap07pPMJmT+PTZP9rbIgUV7sJS4VBR/OP52JoJxCdavsdi02yvd9Ho93HR8hrdVUf8RDBghtaR5RZvA9INJK76SA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713171562; c=relaxed/simple; bh=8w2BtVONyFickq1XCiWz69BDy4G9BOCDPEbPXC6WFcI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=hHNkDyV+QyDgTLJv9qz3dEoStLt7Q28OedWLjfqBJC4EZIdTd23LZGAVkMoAYNcbi6GhoWpyyy5t/w9dWl36RInAHs1+sSL8oa3SK1JZeJQkythhoyViiDfKKO5vY1QDelrOLXNROpOfH7kGFswAs5N4plUaT4zPnhi3TtFx4ac= 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 44A122F; Mon, 15 Apr 2024 01:59:48 -0700 (PDT) Received: from [10.57.75.121] (unknown [10.57.75.121]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E64003F64C; Mon, 15 Apr 2024 01:59:17 -0700 (PDT) Message-ID: <209b9341-8bd0-47fe-b8fd-9a0f02beeab0@arm.com> Date: Mon, 15 Apr 2024 09:59:16 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 2/2] mm/arm64: override clear_young_dirty_ptes() batch helper Content-Language: en-GB To: Lance Yang , akpm@linux-foundation.org Cc: zokeefe@google.com, 21cnbao@gmail.com, shy828301@gmail.com, david@redhat.com, mhocko@suse.com, fengwei.yin@intel.com, xiehuan09@gmail.com, wangkefeng.wang@huawei.com, songmuchun@bytedance.com, peterx@redhat.com, minchan@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20240413002219.71246-1-ioworker0@gmail.com> <20240413002219.71246-3-ioworker0@gmail.com> From: Ryan Roberts In-Reply-To: <20240413002219.71246-3-ioworker0@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 13/04/2024 01:22, Lance Yang wrote: > The per-pte get_and_clear/modify/set approach would result in > unfolding/refolding for contpte mappings on arm64. So we need > to override clear_young_dirty_ptes() for arm64 to avoid it. > > Suggested-by: David Hildenbrand > Suggested-by: Barry Song <21cnbao@gmail.com> > Signed-off-by: Ryan Roberts No, afraid I haven't signed off yet! > Signed-off-by: Lance Yang > --- > arch/arm64/include/asm/pgtable.h | 37 ++++++++++++++++++++++++++++++++ > arch/arm64/mm/contpte.c | 28 ++++++++++++++++++++++++ > 2 files changed, 65 insertions(+) > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > index 9fd8613b2db2..f951774dd2d6 100644 > --- a/arch/arm64/include/asm/pgtable.h > +++ b/arch/arm64/include/asm/pgtable.h > @@ -1223,6 +1223,28 @@ static inline void __wrprotect_ptes(struct mm_struct *mm, unsigned long address, > __ptep_set_wrprotect(mm, address, ptep); > } > > +static inline void __clear_young_dirty_ptes(struct mm_struct *mm, > + unsigned long addr, pte_t *ptep, > + unsigned int nr, cydp_t flags) > +{ > + pte_t pte; > + > + for (;;) { > + pte = __ptep_get(ptep); > + > + if (flags | CYDP_CLEAR_YOUNG) bug: should be bitwise AND (&). > + pte = pte_mkold(pte); > + if (flags | CYDP_CLEAR_DIRTY) > + pte = pte_mkclean(pte); > + > + __set_pte(ptep, pte); The __ptep_get() and __set_pte() are not atomic. This is only safe when you are clearing BOTH access and dirty (as I explained in the previous version). If you are only clearing one of the flags, you will need a similar cmpxchg loop as for __ptep_test_and_clear_young(). Otherwise you can race with the HW and lose information. > + if (--nr == 0) > + break; > + ptep++; > + addr += PAGE_SIZE; > + } > +} > + > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > #define __HAVE_ARCH_PMDP_SET_WRPROTECT > static inline void pmdp_set_wrprotect(struct mm_struct *mm, > @@ -1379,6 +1401,9 @@ extern void contpte_wrprotect_ptes(struct mm_struct *mm, unsigned long addr, > extern int contpte_ptep_set_access_flags(struct vm_area_struct *vma, > unsigned long addr, pte_t *ptep, > pte_t entry, int dirty); > +extern void contpte_clear_young_dirty_ptes(struct mm_struct *mm, > + unsigned long addr, pte_t *ptep, > + unsigned int nr, cydp_t flags); > > static __always_inline void contpte_try_fold(struct mm_struct *mm, > unsigned long addr, pte_t *ptep, pte_t pte) > @@ -1603,6 +1628,17 @@ static inline int ptep_set_access_flags(struct vm_area_struct *vma, > return contpte_ptep_set_access_flags(vma, addr, ptep, entry, dirty); > } > > +#define clear_young_dirty_ptes clear_young_dirty_ptes > +static inline void clear_young_dirty_ptes(struct mm_struct *mm, > + unsigned long addr, pte_t *ptep, > + unsigned int nr, cydp_t flags) > +{ > + if (likely(nr == 1 && !pte_cont(__ptep_get(ptep)))) > + __clear_young_dirty_ptes(mm, addr, ptep, nr, flags); > + else > + contpte_clear_young_dirty_ptes(mm, addr, ptep, nr, flags); > +} > + > #else /* CONFIG_ARM64_CONTPTE */ > > #define ptep_get __ptep_get > @@ -1622,6 +1658,7 @@ static inline int ptep_set_access_flags(struct vm_area_struct *vma, > #define wrprotect_ptes __wrprotect_ptes > #define __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS > #define ptep_set_access_flags __ptep_set_access_flags > +#define clear_young_dirty_ptes __clear_young_dirty_ptes > > #endif /* CONFIG_ARM64_CONTPTE */ > > diff --git a/arch/arm64/mm/contpte.c b/arch/arm64/mm/contpte.c > index 1b64b4c3f8bf..bf3b089d9641 100644 > --- a/arch/arm64/mm/contpte.c > +++ b/arch/arm64/mm/contpte.c > @@ -361,6 +361,34 @@ void contpte_wrprotect_ptes(struct mm_struct *mm, unsigned long addr, > } > EXPORT_SYMBOL_GPL(contpte_wrprotect_ptes); > > +void contpte_clear_young_dirty_ptes(struct mm_struct *mm, unsigned long addr, > + pte_t *ptep, unsigned int nr, cydp_t flags) > +{ > + /* > + * We can safely clear access/dirty without needing to unfold from > + * the architectures perspective, even when contpte is set. If the > + * range starts or ends midway through a contpte block, we can just > + * expand to include the full contpte block. While this is not > + * exactly what the core-mm asked for, it tracks access/dirty per > + * folio, not per page. And since we only create a contpte block > + * when it is covered by a single folio, we can get away with > + * clearing access/dirty for the whole block. > + */ > + unsigned int start = addr; > + unsigned int end = start + nr; There are addresses; they should be unsigned long. May have been my error originally when I sent you the example snippet. Thanks, Ryan > + > + if (pte_cont(__ptep_get(ptep + nr - 1))) > + end = ALIGN(end, CONT_PTE_SIZE); > + > + if (pte_cont(__ptep_get(ptep))) { > + start = ALIGN_DOWN(start, CONT_PTE_SIZE); > + ptep = contpte_align_down(ptep); > + } > + > + __clear_young_dirty_ptes(mm, start, ptep, end - start, flags); > +} > +EXPORT_SYMBOL_GPL(contpte_clear_young_dirty_ptes); > + > int contpte_ptep_set_access_flags(struct vm_area_struct *vma, > unsigned long addr, pte_t *ptep, > pte_t entry, int dirty)