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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Nd9Gvt1qKcpnsc06Gjc+2CD1SNy3cD4To54NY8qil+5DrPmWmULRuTBpzh/zGK1yu rVuKH+uU2mLSs/4M1tFh2Y6ZoZ1KA303+qctE0QLw8ommwu02QKio/26ZzRIL0AofH +OO2lduMz1qH9fvguQf92AJQnwUW3OdkFRvLMmc8= Message-ID: <0944f74c-847a-41a7-bd8f-db9f8dd0fe80@arm.com> Date: Thu, 24 Sep 2026 13:09:55 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V3 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, kasan-dev@googlegroups.com References: <20260924062214.1635078-1-anshuman.khandual@arm.com> <20260924062214.1635078-2-anshuman.khandual@arm.com> From: Ryan Roberts Content-Language: en-GB In-Reply-To: <20260924062214.1635078-2-anshuman.khandual@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: f4t6bqdbyikzioicxf5w8wjknghx1g7b X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 058CA18000B X-HE-Tag: 1790251800-20795 X-HE-Meta: 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 FjH7Xg/s 6geYbRTggq+UxZbAB1ScAkkwWqceqdI3GdNkHjF4YIOjxGpnig+52mLjOeYetN/f8T93vS9NY02O8LVnSKfOgv7B1lY3BWfpaSRxCWxu7vPh3SgUQI40euNlTi3SdzY/l33Eu3P8vx3TQRmyqoqjPgGDBZRt7rszK+b+436Ao8w5MEn6/N7m/y272JfXZvZP8RRyrWbFX94DDNwQN1B+aNOZPuc2JSeaHzIgGFQVMTaMD88OlI4m24/1to98xtOLMRCQSpB7ro7MTdqxpk+IXHrJYERrlHJ3JDyEK+dweTjZO3TVynBRyfmXzL5COAuZ70bRkJkTevmBtOvZDVA+OLkOmuTg+XKwfaCST3VdHJIjlwk6LBNrtH6RV3Wbv9L0UIOQTVCRZ5FsaZSJN4RYxQzRzii6PKAKKCPGF3TxaEP95nHNbofmr4E79/AnKN97UpVFo4X/raxwY7bt4MgaUeP8i02ObEwKcx0+P6NZ92cG40TM= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 24/09/2026 07:22, 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. > > For now override pmdp_get() which is same as the generic memory default > to avoid build dependency problem for callers in header . > > No functional change intended. > > Cc: Catalin Marinas > Cc: Will Deacon > Cc: Ryan Roberts > Cc: Mark Rutland > Cc: linux-arm-kernel@lists.infradead.org > Cc: linux-kernel@vger.kernel.org > Cc: kasan-dev@googlegroups.com > Signed-off-by: Anshuman Khandual Reviewed-by: Ryan Roberts > --- > Changes in V3 > > - Added platform override for pmdp_get() > - Replaced READ_ONCE() in pmdp_test_and_clear_young() > > arch/arm64/include/asm/pgtable.h | 11 +++++++++-- > 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, 27 insertions(+), 20 deletions(-) > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > index 763c5a411d64..9ad2d03e86ad 100644 > --- a/arch/arm64/include/asm/pgtable.h > +++ b/arch/arm64/include/asm/pgtable.h > @@ -84,6 +84,12 @@ static inline void arch_leave_lazy_mmu_mode(void) > arch_flush_lazy_mmu_mode(); > } > > +#define pmdp_get pmdp_get > +static inline pmd_t pmdp_get(pmd_t *pmdp) > +{ > + return READ_ONCE(*pmdp); > +} > + > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > #define __HAVE_ARCH_FLUSH_PMD_TLB_RANGE > > @@ -811,7 +817,8 @@ 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)) > @@ -1291,7 +1298,7 @@ static inline bool pmdp_test_and_clear_young(struct vm_area_struct *vma, > unsigned long address, pmd_t *pmdp) > { > /* Operation applies to PMD table entry only if FEAT_HAFT is enabled */ > - VM_WARN_ON(pmd_table(READ_ONCE(*pmdp)) && !system_supports_haft()); > + VM_WARN_ON(pmd_table(pmdp_get(pmdp)) && !system_supports_haft()); > return __ptep_test_and_clear_young(vma, address, (pte_t *)pmdp); > } > #endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG */ > 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))