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s=arc-20220608; d=hostedemail.com; t=1759821089; a=rsa-sha256; cv=none; b=zZWhLwhtlquZMQtGADgEVHBNMYdzszjD1IBZ5LaGhJR4Wt+Z962EgyeQhCvtcHx8zn8VPL a7hNr7he5ncr+WksIXJTHprc2T/UuC/tIbd8lG7+RJAe6DbFiE8EPTyb9Z5PCeRNrjELOf L65J+643rcjiEt/uDp9xnEDzewdKUKA= ARC-Authentication-Results: i=1; imf15.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf15.hostedemail.com: domain of dev.jain@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=dev.jain@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 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 X-Rspamd-Server: rspam01 X-Stat-Signature: etbxxst5su6exncs6g9qqyd5q7t33c88 X-Rspam-User: X-Rspamd-Queue-Id: 9F118A0009 X-HE-Tag: 1759821089-484713 X-HE-Meta: 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 NwL4RcfL 0xB337+ZTu0uiUqNOZbI3jSjGpjQ1mTV3ppNj/KbCGR+rfQRWr0JMHgRdO/rzDqoQbAaisJV7CcWkTYedBuS2xbZgbTbDUSyeVsyvmPvU6+twWDg00V7nnCtNUh1XZ5cvK5dfmFLgq7rvi/FJ6nUpAh8aALjCiuLA1F9MFFjXRkMDSvnVkmaMxttWToUyYuYYIsKCGF3BJWstyRkIOWbmWVlcGVaRBAb2y6dROCzRObV1u0YJvQ0EUhBtfYWoB5LVCs5yaHmRmEceDZK5FmbJxdYX8m8hCns1zMVXbJf4GKv0S0Hyo2HJp0QE3mNFyhY5MJTCCzXh9hfCx3oQXrakd793cb9G7bI9PH6NbMLqfioaQIpH1UgE/mz8lqvB1LjF8TwvUPETiwtvRDeVJvw745zZgBlwFQz5CnhkQj4s+U1rTbDi0PDMMxbTVZy1dd+U36Iy 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: List-Subscribe: List-Unsubscribe: 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); >