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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=t8ia1hWnCTKF6BgRjNTh6Q94B8/wFBEFP1mNHioecYtl12XVSfSCern/A1uvo/OZU TiCDYoVmCM3MzNfdFbfDWzlLLfsu5csrVYQMg3i2gkYqyGCYyFxz29vQWHWJDFa8Ha +uBVE/omKsioocOpkO9vW2NLdXR82bDe/iVQmYnM= Message-ID: <212067fe-1b16-4b87-87a7-4ce50847eb24@arm.com> Date: Wed, 23 Sep 2026 09:32:17 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V2 1/4] arm64/mm: Use pmdp_get() for PMD accesses To: Anshuman Khandual , linux-arm-kernel@lists.infradead.org Cc: Catalin Marinas , Will Deacon , Mark Rutland , Lorenzo Stoakes , Andrew Morton , David Hildenbrand , Mike Rapoport , Linu Cherian , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Mark Rtland , linx-arm-kernel@lists.infradead.org, linx-kernel@vger.kernel.org, kasan-dev@googlegrops.com References: <20260922061638.3967467-1-anshuman.khandual@arm.com> <20260922061638.3967467-2-anshuman.khandual@arm.com> From: Ryan Roberts Content-Language: en-GB In-Reply-To: <20260922061638.3967467-2-anshuman.khandual@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: esobpt8mqa6qqh9xic3bpu4j7rmobqds X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: CCF7E100004 X-HE-Tag: 1790152343-811457 X-HE-Meta: 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 OwVbfwT6 yMpaMGWpomdtGDrW+b3el6LrAb8nI33EpSjlZyYAJxXmNzV6igXrqz1az8IwbPlzh1ym3gU2LUUZdU40rFDG4hZixhpEKKvGVUT3KZ4gsoMJPOwoe18aEbnMH6rzwWIW/PM01o/7I7XLZe+AKbs8c96yFoloU5Wa+k0++HANQmvK9Nj0rTItJWxmzGGz9L5/ad+Y20RvYD6pk+wYLA3WgHPXHLVAF4EleNI9sh2/qTYszrO/wb31BYbWh3sUFuHzLbi0vQhAwjAFXL2QAgcfZNIhGNiD0NXWJbVsUUVCIUYWpvd9r4jNeehaILTVErJ/Dbjht/pnuoLq0cR68/D0RdBFjQtZcO3EWTelAmSpm4z8bmoyu47LgwUBRynvNZiEoRZUr/f3opgv92MgrNlcLketH7QnzjvuiOp1RyZSuZGytjvRhn6kqp4FrM7itDLHnqbLZQki1QFlcDwlSBSiU1gMuFAoaIVXm6TcjK/nUSpQMWvY= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 22/09/2026 07:16, Anshuman Khandual wrote: > Replace READ_ONCE() with pmdp_get() for PMD accesses in preparation for > supporting both D64 and D128 translation table formats. > > READ_ONCE() cannot currently be used for 128-bit page table entries on > arm64 because it does not provide the required 128-bit single-copy > atomicity, causing builds to fail for accesses wider than 64 bits. > > Although LDP/STP provide the required atomicity when FEAT_LSE is > available (as required by FEAT_D128), extending READ_ONCE() to support > 128-bit accesses is undesirable. READ_ONCE() is a general-purpose API, > so doing so could encourage other 128-bit users that would either fail > to build in configurations without D128 support or, if D128 becomes a > runtime option, silently permit tearing on systems without the required > hardware support. > > Instead, standardize PMD accesses on the existing page-table helpers. > These can be overridden on arm64 to provide 128-bit single-copy > atomicity when required. No functional change intended. I notice you have an unconverted READ_ONCE(*pmdp) in pmdp_test_and_clear_young(). Is that intentional? Thanks, Ryan > > Cc: Catalin Marinas > Cc: Will Deacon > Cc: Ryan Roberts > Cc: Mark Rtland > Cc: linx-arm-kernel@lists.infradead.org > Cc: linx-kernel@vger.kernel.org > Cc: kasan-dev@googlegrops.com > Reviewed-by: Ryan Roberts > Signed-off-by: Anshuman Khandual > --- > arch/arm64/include/asm/pgtable.h | 3 ++- > arch/arm64/mm/fault.c | 2 +- > arch/arm64/mm/fixmap.c | 2 +- > arch/arm64/mm/hugetlbpage.c | 2 +- > arch/arm64/mm/kasan_init.c | 4 ++-- > arch/arm64/mm/mmu.c | 22 +++++++++++----------- > arch/arm64/mm/pageattr.c | 2 +- > arch/arm64/mm/trans_pgd.c | 2 +- > 8 files changed, 20 insertions(+), 19 deletions(-) > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > index 763c5a411d64..b953ea0ba3ed 100644 > --- a/arch/arm64/include/asm/pgtable.h > +++ b/arch/arm64/include/asm/pgtable.h > @@ -811,7 +811,8 @@ static inline unsigned long pmd_page_vaddr(pmd_t pmd) > } > > /* Find an entry in the third-level page table. */ > -#define pte_offset_phys(dir,addr) (pmd_page_paddr(READ_ONCE(*(dir))) + pte_index(addr) * sizeof(pte_t)) > +#define pte_offset_phys(dir, addr) (pmd_page_paddr(pmdp_get(dir)) + \ > + pte_index(addr) * sizeof(pte_t)) > > #define pte_set_fixmap(addr) ((pte_t *)set_fixmap_offset(FIX_PTE, addr)) > #define pte_set_fixmap_offset(pmd, addr) pte_set_fixmap(pte_offset_phys(pmd, addr)) > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c > index 2cecf6ba6df7..2757ee0c4300 100644 > --- a/arch/arm64/mm/fault.c > +++ b/arch/arm64/mm/fault.c > @@ -188,7 +188,7 @@ static void show_pte(unsigned long addr) > break; > > pmdp = pmd_offset_lockless(pudp, pud, addr); > - pmd = READ_ONCE(*pmdp); > + pmd = pmdp_get(pmdp); > ptval_to_str(pxd_str, pmd_val(pmd)); > pr_cont(", pmd=%s", pxd_str); > if (pmd_none(pmd) || pmd_bad(pmd)) > diff --git a/arch/arm64/mm/fixmap.c b/arch/arm64/mm/fixmap.c > index f66a0016dd02..3cdac8021d4f 100644 > --- a/arch/arm64/mm/fixmap.c > +++ b/arch/arm64/mm/fixmap.c > @@ -42,7 +42,7 @@ static inline pte_t *fixmap_pte(unsigned long addr) > > static void __init early_fixmap_init_pte(pmd_t *pmdp, unsigned long addr) > { > - pmd_t pmd = READ_ONCE(*pmdp); > + pmd_t pmd = pmdp_get(pmdp); > pte_t *ptep; > > if (pmd_none(pmd)) { > diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c > index 8e799c1fe0aa..cdaa4500faf9 100644 > --- a/arch/arm64/mm/hugetlbpage.c > +++ b/arch/arm64/mm/hugetlbpage.c > @@ -304,7 +304,7 @@ pte_t *huge_pte_offset(struct mm_struct *mm, > addr &= CONT_PMD_MASK; > > pmdp = pmd_offset(pudp, addr); > - pmd = READ_ONCE(*pmdp); > + pmd = pmdp_get(pmdp); > if (!(sz == PMD_SIZE || sz == CONT_PMD_SIZE) && > pmd_none(pmd)) > return NULL; > diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c > index 45fbdce684c8..7ca833c5de5e 100644 > --- a/arch/arm64/mm/kasan_init.c > +++ b/arch/arm64/mm/kasan_init.c > @@ -62,7 +62,7 @@ static phys_addr_t __init kasan_alloc_raw_page(int node) > static pte_t *__init kasan_pte_offset(pmd_t *pmdp, unsigned long addr, int node, > bool early) > { > - if (pmd_none(READ_ONCE(*pmdp))) { > + if (pmd_none(pmdp_get(pmdp))) { > phys_addr_t pte_phys = early ? > __pa_symbol(kasan_early_shadow_pte) > : kasan_alloc_zeroed_page(node); > @@ -138,7 +138,7 @@ static void __init kasan_pmd_populate(pud_t *pudp, unsigned long addr, > do { > next = pmd_addr_end(addr, end); > kasan_pte_populate(pmdp, addr, next, node, early); > - } while (pmdp++, addr = next, addr != end && pmd_none(READ_ONCE(*pmdp))); > + } while (pmdp++, addr = next, addr != end && pmd_none(pmdp_get(pmdp))); > } > > static void __init kasan_pud_populate(p4d_t *p4dp, unsigned long addr, > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index e589fb00d1e3..95621913679e 100644 > --- a/arch/arm64/mm/mmu.c > +++ b/arch/arm64/mm/mmu.c > @@ -200,7 +200,7 @@ static int alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr, > int flags) > { > unsigned long next; > - pmd_t pmd = READ_ONCE(*pmdp); > + pmd_t pmd = pmdp_get(pmdp); > pte_t *ptep; > > BUG_ON(pmd_leaf(pmd)); > @@ -257,7 +257,7 @@ static int init_pmd(pmd_t *pmdp, unsigned long addr, unsigned long end, > unsigned long next; > > do { > - pmd_t old_pmd = READ_ONCE(*pmdp); > + pmd_t old_pmd = pmdp_get(pmdp); > > next = pmd_addr_end(addr, end); > > @@ -272,7 +272,7 @@ static int init_pmd(pmd_t *pmdp, unsigned long addr, unsigned long end, > * only allow updates to the permission attributes. > */ > BUG_ON(!pgattr_change_is_safe(pmd_val(old_pmd), > - READ_ONCE(pmd_val(*pmdp)))); > + pmd_val(pmdp_get(pmdp)))); > } else { > int ret; > > @@ -282,7 +282,7 @@ static int init_pmd(pmd_t *pmdp, unsigned long addr, unsigned long end, > return ret; > > VM_WARN_ON_ONCE(pmd_val(old_pmd) != 0 && > - pmd_val(old_pmd) != READ_ONCE(pmd_val(*pmdp))); > + pmd_val(old_pmd) != pmd_val(pmdp_get(pmdp))); > } > phys += next - addr; > } while (pmdp++, addr = next, addr != end); > @@ -293,7 +293,7 @@ static int init_pmd(pmd_t *pmdp, unsigned long addr, unsigned long end, > static bool pmd_range_has_valid_noncont(pmd_t *pmdp) > { > for (int i = 0; i < CONT_PMDS; i++) { > - pte_t pte = pmd_pte(READ_ONCE(pmdp[i])); > + pte_t pte = pmd_pte(pmdp_get(pmdp + i)); > > if (pte_valid(pte) && !pte_cont(pte)) > return true; > @@ -1553,7 +1553,7 @@ static void unmap_hotplug_pmd_range(pud_t *pudp, unsigned long addr, > do { > next = pmd_addr_end(addr, end); > pmdp = pmd_offset(pudp, addr); > - pmd = READ_ONCE(*pmdp); > + pmd = pmdp_get(pmdp); > if (pmd_none(pmd)) > continue; > > @@ -1708,7 +1708,7 @@ static void free_empty_pmd_table(pud_t *pudp, unsigned long addr, > do { > next = pmd_addr_end(addr, end); > pmdp = pmd_offset(pudp, addr); > - pmd = READ_ONCE(*pmdp); > + pmd = pmdp_get(pmdp); > if (pmd_none(pmd)) > continue; > > @@ -1729,7 +1729,7 @@ static void free_empty_pmd_table(pud_t *pudp, unsigned long addr, > */ > pmdp = pmd_offset(pudp, 0UL); > for (i = 0; i < PTRS_PER_PMD; i++) { > - if (!pmd_none(READ_ONCE(pmdp[i]))) > + if (!pmd_none(pmdp_get(pmdp + i))) > return; > } > > @@ -1881,7 +1881,7 @@ int pmd_set_huge(pmd_t *pmdp, phys_addr_t phys, pgprot_t prot) > pmd_t new_pmd = pfn_pmd(__phys_to_pfn(phys), mk_pmd_sect_prot(prot)); > > /* Only allow permission changes for now */ > - if (!pgattr_change_is_safe(READ_ONCE(pmd_val(*pmdp)), > + if (!pgattr_change_is_safe(pmd_val(pmdp_get(pmdp)), > pmd_val(new_pmd))) > return 0; > > @@ -1906,7 +1906,7 @@ int pud_clear_huge(pud_t *pudp) > > int pmd_clear_huge(pmd_t *pmdp) > { > - if (!pmd_leaf(READ_ONCE(*pmdp))) > + if (!pmd_leaf(pmdp_get(pmdp))) > return 0; > pmd_clear(pmdp); > return 1; > @@ -1917,7 +1917,7 @@ int pmd_free_pte_page(pmd_t *pmdp, unsigned long addr) > pte_t *table; > pmd_t pmd; > > - pmd = READ_ONCE(*pmdp); > + pmd = pmdp_get(pmdp); > > if (!pmd_table(pmd)) { > VM_WARN_ON(1); > diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c > index bbe98ac9ad8c..0ca07bd5ded9 100644 > --- a/arch/arm64/mm/pageattr.c > +++ b/arch/arm64/mm/pageattr.c > @@ -414,7 +414,7 @@ bool kernel_page_present(struct page *page) > return pud_valid(pud); > > pmdp = pmd_offset(pudp, addr); > - pmd = READ_ONCE(*pmdp); > + pmd = pmdp_get(pmdp); > if (pmd_none(pmd)) > return false; > if (pmd_leaf(pmd)) > diff --git a/arch/arm64/mm/trans_pgd.c b/arch/arm64/mm/trans_pgd.c > index cca9706a875c..b27b2d2c20c3 100644 > --- a/arch/arm64/mm/trans_pgd.c > +++ b/arch/arm64/mm/trans_pgd.c > @@ -74,7 +74,7 @@ static int copy_pmd(struct trans_pgd_info *info, pud_t *dst_pudp, > > src_pmdp = pmd_offset(src_pudp, start); > do { > - pmd_t pmd = READ_ONCE(*src_pmdp); > + pmd_t pmd = pmdp_get(src_pmdp); > > next = pmd_addr_end(addr, end); > if (pmd_none(pmd))