Let's use the newly-free PTE SW bit (58) to add support for uffd-wp.
The standard handlers are implemented for set/test/clear for both pte and pmd. Additionally we must also track the uffd-wp state as a pte swp bit, so use a free swap entry pte bit (3).
Signed-off-by: Ryan Roberts ryan.roberts@arm.com --- arch/arm64/Kconfig | 1 + arch/arm64/include/asm/pgtable-prot.h | 8 ++++ arch/arm64/include/asm/pgtable.h | 55 +++++++++++++++++++++++++++ 3 files changed, 64 insertions(+)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 7b11c98b3e84..763e221f2169 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -255,6 +255,7 @@ config ARM64 select SYSCTL_EXCEPTION_TRACE select THREAD_INFO_IN_TASK select HAVE_ARCH_USERFAULTFD_MINOR if USERFAULTFD + select HAVE_ARCH_USERFAULTFD_WP if USERFAULTFD select TRACE_IRQFLAGS_SUPPORT select TRACE_IRQFLAGS_NMI_SUPPORT select HAVE_SOFTIRQ_ON_OWN_STACK diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h index ef952d69fd04..f1e1f6306e03 100644 --- a/arch/arm64/include/asm/pgtable-prot.h +++ b/arch/arm64/include/asm/pgtable-prot.h @@ -20,6 +20,14 @@ #define PTE_DEVMAP (_AT(pteval_t, 1) << 57) #define PTE_PROT_NONE (PTE_UXN) /* Reuse PTE_UXN; only when !PTE_VALID */
+#ifdef CONFIG_HAVE_ARCH_USERFAULTFD_WP +#define PTE_UFFD_WP (_AT(pteval_t, 1) << 58) /* uffd-wp tracking */ +#define PTE_SWP_UFFD_WP (_AT(pteval_t, 1) << 3) /* only for swp ptes */ +#else +#define PTE_UFFD_WP (_AT(pteval_t, 0)) +#define PTE_SWP_UFFD_WP (_AT(pteval_t, 0)) +#endif /* CONFIG_HAVE_ARCH_USERFAULTFD_WP */ + /* * This bit indicates that the entry is present i.e. pmd_page() * still points to a valid huge page in memory even if the pmd diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h index 23aabff4fa6f..3f4748741fdb 100644 --- a/arch/arm64/include/asm/pgtable.h +++ b/arch/arm64/include/asm/pgtable.h @@ -271,6 +271,34 @@ static inline pte_t pte_mkdevmap(pte_t pte) return set_pte_bit(pte, __pgprot(PTE_DEVMAP | PTE_SPECIAL)); }
+#ifdef CONFIG_HAVE_ARCH_USERFAULTFD_WP +static inline int pte_uffd_wp(pte_t pte) +{ + bool wp = !!(pte_val(pte) & PTE_UFFD_WP); + +#ifdef CONFIG_DEBUG_VM + /* + * Having write bit for wr-protect-marked present ptes is fatal, because + * it means the uffd-wp bit will be ignored and write will just go + * through. See comment in x86 implementation. + */ + WARN_ON_ONCE(wp && pte_write(pte)); +#endif + + return wp; +} + +static inline pte_t pte_mkuffd_wp(pte_t pte) +{ + return pte_wrprotect(set_pte_bit(pte, __pgprot(PTE_UFFD_WP))); +} + +static inline pte_t pte_clear_uffd_wp(pte_t pte) +{ + return clear_pte_bit(pte, __pgprot(PTE_UFFD_WP)); +} +#endif /* CONFIG_HAVE_ARCH_USERFAULTFD_WP */ + static inline void __set_pte(pte_t *ptep, pte_t pte) { WRITE_ONCE(*ptep, pte); @@ -463,6 +491,23 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte) return clear_pte_bit(pte, __pgprot(PTE_SWP_EXCLUSIVE)); }
+#ifdef CONFIG_HAVE_ARCH_USERFAULTFD_WP +static inline pte_t pte_swp_mkuffd_wp(pte_t pte) +{ + return set_pte_bit(pte, __pgprot(PTE_SWP_UFFD_WP)); +} + +static inline int pte_swp_uffd_wp(pte_t pte) +{ + return !!(pte_val(pte) & PTE_SWP_UFFD_WP); +} + +static inline pte_t pte_swp_clear_uffd_wp(pte_t pte) +{ + return clear_pte_bit(pte, __pgprot(PTE_SWP_UFFD_WP)); +} +#endif /* CONFIG_HAVE_ARCH_USERFAULTFD_WP */ + #ifdef CONFIG_NUMA_BALANCING /* * See the comment in include/linux/pgtable.h @@ -508,6 +553,15 @@ static inline int pmd_trans_huge(pmd_t pmd) #define pmd_mkclean(pmd) pte_pmd(pte_mkclean(pmd_pte(pmd))) #define pmd_mkdirty(pmd) pte_pmd(pte_mkdirty(pmd_pte(pmd))) #define pmd_mkyoung(pmd) pte_pmd(pte_mkyoung(pmd_pte(pmd))) +#ifdef CONFIG_HAVE_ARCH_USERFAULTFD_WP +#define pmd_uffd_wp(pmd) pte_uffd_wp(pmd_pte(pmd)) +#define pmd_mkuffd_wp(pmd) pte_pmd(pte_mkuffd_wp(pmd_pte(pmd))) +#define pmd_clear_uffd_wp(pmd) pte_pmd(pte_clear_uffd_wp(pmd_pte(pmd))) +#define pmd_swp_uffd_wp(pmd) pte_swp_uffd_wp(pmd_pte(pmd)) +#define pmd_swp_mkuffd_wp(pmd) pte_pmd(pte_swp_mkuffd_wp(pmd_pte(pmd))) +#define pmd_swp_clear_uffd_wp(pmd) \ + pte_pmd(pte_swp_clear_uffd_wp(pmd_pte(pmd))) +#endif /* CONFIG_HAVE_ARCH_USERFAULTFD_WP */
static inline pmd_t pmd_mkinvalid(pmd_t pmd) { @@ -1248,6 +1302,7 @@ static inline pmd_t pmdp_establish(struct vm_area_struct *vma, * Encode and decode a swap entry: * bits 0-1: present (must be zero) * bits 2: remember PG_anon_exclusive + * bit 3: remember uffd-wp state * bits 4-53: swap offset * bit 54: PTE_PROT_NONE (overlays PTE_UXN) (must be zero) * bits 55-59: swap type -- 2.25.1