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 1C2E22253EE for ; Tue, 7 Oct 2025 07:11:28 +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=1759821091; cv=none; b=QPyGQzrgeac1gotPDfXWVrEW2CIjATirFdnNJ5LQuR/shkD3SbmlqOmAhMBLm92A74LVYrlgnf5h3/piXonaVukB74MGagbvKscEKJHi8Wm1OcgHVW0MDkBg5/rTiiauMtjVOcQo6gzCedhzGVJ0KxifjAUAZgoyClFtnpynbh8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759821091; c=relaxed/simple; bh=LadauiYqFa0FVLNi6UteWLgji4+EmhJAL0p4QNPxgCE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=KtSSyy96ImAPf7uvWDbQiIlGxpusNdBPKRvOlFYBhxOnyMnDJmYRRXDAptLbaT6tpCy6HpkxO6xIOahDMCMvruDbk3vFRsN8wCquxIvxdWP8+ElTwrlcJY8fWlhl6hE2UxFsdEtiHk0isszcraagA760JvyhVPnXclmxHop4rYw= 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 7A79914BF; Tue, 7 Oct 2025 00:11:20 -0700 (PDT) Received: from [10.163.65.24] (unknown [10.163.65.24]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 76B623F66E; Tue, 7 Oct 2025 00:11:26 -0700 (PDT) Message-ID: <584fea72-e564-4cf6-9435-ce4b03f2fd65@arm.com> Date: Tue, 7 Oct 2025 12:41:22 +0530 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] mm: Replace READ_ONCE() with standard page table accessors To: Anshuman Khandual , linux-mm@kvack.org Cc: Andrew Morton , David Hildenbrand , linux-kernel@vger.kernel.org References: <20251007063100.2396936-1-anshuman.khandual@arm.com> Content-Language: en-US From: Dev Jain In-Reply-To: <20251007063100.2396936-1-anshuman.khandual@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 07/10/25 12:01 pm, Anshuman Khandual wrote: > Replace all READ_ONCE() with a standard page table accessors i.e pxdp_get() > that defaults into READ_ONCE() in cases where platform does not override. Does any platform override into something else currently? The way you write the description implies that. > > Cc: Andrew Morton > Cc: David Hildenbrand > Cc: linux-mm@kvack.org > Cc: linux-kernel@vger.kernel.org > Signed-off-by: Anshuman Khandual > --- > mm/gup.c | 10 +++++----- > mm/hmm.c | 2 +- > mm/memory.c | 4 ++-- > mm/mprotect.c | 2 +- > mm/sparse-vmemmap.c | 2 +- > mm/vmscan.c | 2 +- > 6 files changed, 11 insertions(+), 11 deletions(-) > > diff --git a/mm/gup.c b/mm/gup.c > index 0bc4d140fc07..37e2af5ed96d 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -964,7 +964,7 @@ static struct page *follow_pud_mask(struct vm_area_struct *vma, > struct mm_struct *mm = vma->vm_mm; > > pudp = pud_offset(p4dp, address); > - pud = READ_ONCE(*pudp); > + pud = pudp_get(pudp); > if (!pud_present(pud)) > return no_page_table(vma, flags, address); > if (pud_leaf(pud)) { > @@ -989,7 +989,7 @@ static struct page *follow_p4d_mask(struct vm_area_struct *vma, > p4d_t *p4dp, p4d; > > p4dp = p4d_offset(pgdp, address); > - p4d = READ_ONCE(*p4dp); > + p4d = p4dp_get(p4dp); > BUILD_BUG_ON(p4d_leaf(p4d)); > > if (!p4d_present(p4d) || p4d_bad(p4d)) > @@ -3080,7 +3080,7 @@ static int gup_fast_pud_range(p4d_t *p4dp, p4d_t p4d, unsigned long addr, > > pudp = pud_offset_lockless(p4dp, p4d, addr); > do { > - pud_t pud = READ_ONCE(*pudp); > + pud_t pud = pudp_get(pudp); > > next = pud_addr_end(addr, end); > if (unlikely(!pud_present(pud))) > @@ -3106,7 +3106,7 @@ static int gup_fast_p4d_range(pgd_t *pgdp, pgd_t pgd, unsigned long addr, > > p4dp = p4d_offset_lockless(pgdp, pgd, addr); > do { > - p4d_t p4d = READ_ONCE(*p4dp); > + p4d_t p4d = p4dp_get(p4dp); > > next = p4d_addr_end(addr, end); > if (!p4d_present(p4d)) > @@ -3128,7 +3128,7 @@ static void gup_fast_pgd_range(unsigned long addr, unsigned long end, > > pgdp = pgd_offset(current->mm, addr); > do { > - pgd_t pgd = READ_ONCE(*pgdp); > + pgd_t pgd = pgdp_get(pgdp); > > next = pgd_addr_end(addr, end); > if (pgd_none(pgd)) > diff --git a/mm/hmm.c b/mm/hmm.c > index d545e2494994..126c3f42e525 100644 > --- a/mm/hmm.c > +++ b/mm/hmm.c > @@ -431,7 +431,7 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end, > /* Normally we don't want to split the huge page */ > walk->action = ACTION_CONTINUE; > > - pud = READ_ONCE(*pudp); > + pud = pudp_get(pudp); > if (!pud_present(pud)) { > spin_unlock(ptl); > return hmm_vma_walk_hole(start, end, -1, walk); > diff --git a/mm/memory.c b/mm/memory.c > index 0ba4f6b71847..50f841ee6e84 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -6549,12 +6549,12 @@ int follow_pfnmap_start(struct follow_pfnmap_args *args) > goto out; > > p4dp = p4d_offset(pgdp, address); > - p4d = READ_ONCE(*p4dp); > + p4d = p4dp_get(p4dp); > if (p4d_none(p4d) || unlikely(p4d_bad(p4d))) > goto out; > > pudp = pud_offset(p4dp, address); > - pud = READ_ONCE(*pudp); > + pud = pudp_get(pudp); > if (pud_none(pud)) > goto out; > if (pud_leaf(pud)) { > diff --git a/mm/mprotect.c b/mm/mprotect.c > index 113b48985834..988c366137d5 100644 > --- a/mm/mprotect.c > +++ b/mm/mprotect.c > @@ -599,7 +599,7 @@ static inline long change_pud_range(struct mmu_gather *tlb, > break; > } > > - pud = READ_ONCE(*pudp); > + pud = pudp_get(pudp); > if (pud_none(pud)) > continue; > > diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c > index dbd8daccade2..37522d6cb398 100644 > --- a/mm/sparse-vmemmap.c > +++ b/mm/sparse-vmemmap.c > @@ -439,7 +439,7 @@ int __meminit vmemmap_populate_hugepages(unsigned long start, unsigned long end, > return -ENOMEM; > > pmd = pmd_offset(pud, addr); > - if (pmd_none(READ_ONCE(*pmd))) { > + if (pmd_none(pmdp_get(pmd))) { I believe sparse-vmemmap is only for 64 bit arches so we are safe. > void *p; > > p = vmemmap_alloc_block_buf(PMD_SIZE, node, altmap); > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 674999999cd0..14c2722b955b 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -3772,7 +3772,7 @@ static int walk_pud_range(p4d_t *p4d, unsigned long start, unsigned long end, > pud = pud_offset(p4d, start & P4D_MASK); > restart: > for (i = pud_index(start), addr = start; addr != end; i++, addr = next) { > - pud_t val = READ_ONCE(pud[i]); > + pud_t val = pudp_get(pud + i); > > next = pud_addr_end(addr, end); >