Use the final remaining PTE SW bit (63) for soft-dirty tracking. The standard handlers are implemented for set/test/clear for both pte and pmd. Additionally we must also track the soft-dirty state as a pte swp bit, so use a free swap entry pte bit (61).
There are a few complexities worth calling out:
- The semantic of soft-dirty calls for having it auto-set by pte_mkdirty(). But the arch code would previously call pte_mkdirty() for various house-keeping operations such as gathering dirty bits into a pte across a contpte block. These operations must not cause soft-dirty to be set. So an internal version, __pte_mkdirty(), has been created that does not manipulate soft-dirty, and pte_mkdirty() is now a wrapper around that, which also sets the soft-dirty bit.
- For a region with soft-dirty tracking enabled, it works by wrprotecting the ptes, causing a write to fault, where the handler calls pte_mkdirty(ptep_get()) (which causes soft-dirty to be set), then the resulting pte is written back with ptep_set_access_flags(). So the arm64 version of ptep_set_access_flags() now needs to explicitly also set the soft-dirty bit to prevent loss.
The patch is very loosely based on a similar patch posted by Shivansh Vij shivanshvij@outlook.com, at the below link.
Primary motivation for adding soft-dirty support is to allow Checkpoint-Restore in Userspace (CRIU) to be able to track a memory page's changes if we want to enable pre-dumping, which is important for live migration.
Link: https://lore.kernel.org/linux-arm-kernel/MW4PR12MB687563EFB56373E8D55DDEABB9... 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 | 47 +++++++++++++++++++++++++-- arch/arm64/mm/contpte.c | 6 ++-- arch/arm64/mm/fault.c | 3 +- arch/arm64/mm/hugetlbpage.c | 6 ++-- 6 files changed, 61 insertions(+), 10 deletions(-)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 763e221f2169..3a5e22208e38 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -178,6 +178,7 @@ config ARM64 select HAVE_ARCH_PREL32_RELOCATIONS select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET select HAVE_ARCH_SECCOMP_FILTER + select HAVE_ARCH_SOFT_DIRTY select HAVE_ARCH_STACKLEAK select HAVE_ARCH_THREAD_STRUCT_WHITELIST select HAVE_ARCH_TRACEHOOK diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h index f1e1f6306e03..7fce22ed3fda 100644 --- a/arch/arm64/include/asm/pgtable-prot.h +++ b/arch/arm64/include/asm/pgtable-prot.h @@ -28,6 +28,14 @@ #define PTE_SWP_UFFD_WP (_AT(pteval_t, 0)) #endif /* CONFIG_HAVE_ARCH_USERFAULTFD_WP */
+#ifdef CONFIG_MEM_SOFT_DIRTY +#define PTE_SOFT_DIRTY (_AT(pteval_t, 1) << 63) /* soft-dirty tracking */ +#define PTE_SWP_SOFT_DIRTY (_AT(pteval_t, 1) << 61) /* only for swp ptes */ +#else +#define PTE_SOFT_DIRTY (_AT(pteval_t, 0)) +#define PTE_SWP_SOFT_DIRTY (_AT(pteval_t, 0)) +#endif /* CONFIG_MEM_SOFT_DIRTY */ + /* * 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 3f4748741fdb..0118e6e0adde 100644 --- a/arch/arm64/include/asm/pgtable.h +++ b/arch/arm64/include/asm/pgtable.h @@ -114,6 +114,7 @@ static inline pteval_t __phys_to_pte_val(phys_addr_t phys) #define pte_user_exec(pte) (!(pte_val(pte) & PTE_UXN)) #define pte_cont(pte) (!!(pte_val(pte) & PTE_CONT)) #define pte_devmap(pte) (!!(pte_val(pte) & PTE_DEVMAP)) +#define pte_soft_dirty(pte) (!!(pte_val(pte) & PTE_SOFT_DIRTY)) #define pte_tagged(pte) ((pte_val(pte) & PTE_ATTRINDX_MASK) == \ PTE_ATTRINDX(MT_NORMAL_TAGGED))
@@ -206,7 +207,7 @@ static inline pte_t pte_mkclean(pte_t pte) return pte; }
-static inline pte_t pte_mkdirty(pte_t pte) +static inline pte_t __pte_mkdirty(pte_t pte) { pte = set_pte_bit(pte, __pgprot(PTE_DIRTY));
@@ -216,6 +217,11 @@ static inline pte_t pte_mkdirty(pte_t pte) return pte; }
+static inline pte_t pte_mkdirty(pte_t pte) +{ + return __pte_mkdirty(set_pte_bit(pte, __pgprot(PTE_SOFT_DIRTY))); +} + static inline pte_t pte_wrprotect(pte_t pte) { /* @@ -299,6 +305,16 @@ static inline pte_t pte_clear_uffd_wp(pte_t pte) } #endif /* CONFIG_HAVE_ARCH_USERFAULTFD_WP */
+static inline pte_t pte_mksoft_dirty(pte_t pte) +{ + return set_pte_bit(pte, __pgprot(PTE_SOFT_DIRTY)); +} + +static inline pte_t pte_clear_soft_dirty(pte_t pte) +{ + return clear_pte_bit(pte, __pgprot(PTE_SOFT_DIRTY)); +} + static inline void __set_pte(pte_t *ptep, pte_t pte) { WRITE_ONCE(*ptep, pte); @@ -508,6 +524,21 @@ static inline pte_t pte_swp_clear_uffd_wp(pte_t pte) } #endif /* CONFIG_HAVE_ARCH_USERFAULTFD_WP */
+static inline pte_t pte_swp_mksoft_dirty(pte_t pte) +{ + return set_pte_bit(pte, __pgprot(PTE_SWP_SOFT_DIRTY)); +} + +static inline bool pte_swp_soft_dirty(pte_t pte) +{ + return !!(pte_val(pte) & PTE_SWP_SOFT_DIRTY); +} + +static inline pte_t pte_swp_clear_soft_dirty(pte_t pte) +{ + return clear_pte_bit(pte, __pgprot(PTE_SWP_SOFT_DIRTY)); +} + #ifdef CONFIG_NUMA_BALANCING /* * See the comment in include/linux/pgtable.h @@ -562,6 +593,15 @@ static inline int pmd_trans_huge(pmd_t pmd) #define pmd_swp_clear_uffd_wp(pmd) \ pte_pmd(pte_swp_clear_uffd_wp(pmd_pte(pmd))) #endif /* CONFIG_HAVE_ARCH_USERFAULTFD_WP */ +#define pmd_soft_dirty(pmd) pte_soft_dirty(pmd_pte(pmd)) +#define pmd_mksoft_dirty(pmd) pte_pmd(pte_mksoft_dirty(pmd_pte(pmd))) +#define pmd_clear_soft_dirty(pmd) \ + pte_pmd(pte_clear_soft_dirty(pmd_pte(pmd))) +#define pmd_swp_soft_dirty(pmd) pte_swp_soft_dirty(pmd_pte(pmd)) +#define pmd_swp_mksoft_dirty(pmd) \ + pte_pmd(pte_swp_mksoft_dirty(pmd_pte(pmd))) +#define pmd_swp_clear_soft_dirty(pmd) \ + pte_pmd(pte_swp_clear_soft_dirty(pmd_pte(pmd)))
static inline pmd_t pmd_mkinvalid(pmd_t pmd) { @@ -1093,7 +1133,7 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot) * dirtiness again. */ if (pte_sw_dirty(pte)) - pte = pte_mkdirty(pte); + pte = __pte_mkdirty(pte); return pte; }
@@ -1228,7 +1268,7 @@ static inline pte_t __get_and_clear_full_ptes(struct mm_struct *mm, addr += PAGE_SIZE; tmp_pte = __ptep_get_and_clear(mm, addr, ptep); if (pte_dirty(tmp_pte)) - pte = pte_mkdirty(pte); + pte = __pte_mkdirty(pte); if (pte_young(tmp_pte)) pte = pte_mkyoung(pte); } @@ -1307,6 +1347,7 @@ static inline pmd_t pmdp_establish(struct vm_area_struct *vma, * bit 54: PTE_PROT_NONE (overlays PTE_UXN) (must be zero) * bits 55-59: swap type * bit 60: PMD_PRESENT_INVALID (must be zero) + * bit 61: remember soft-dirty state */ #define __SWP_TYPE_SHIFT 55 #define __SWP_TYPE_BITS 5 diff --git a/arch/arm64/mm/contpte.c b/arch/arm64/mm/contpte.c index 1b64b4c3f8bf..c6f52fcf5d9a 100644 --- a/arch/arm64/mm/contpte.c +++ b/arch/arm64/mm/contpte.c @@ -62,7 +62,7 @@ static void contpte_convert(struct mm_struct *mm, unsigned long addr, pte_t ptent = __ptep_get_and_clear(mm, addr, ptep);
if (pte_dirty(ptent)) - pte = pte_mkdirty(pte); + pte = __pte_mkdirty(pte);
if (pte_young(ptent)) pte = pte_mkyoung(pte); @@ -170,7 +170,7 @@ pte_t contpte_ptep_get(pte_t *ptep, pte_t orig_pte) pte = __ptep_get(ptep);
if (pte_dirty(pte)) - orig_pte = pte_mkdirty(orig_pte); + orig_pte = __pte_mkdirty(orig_pte);
if (pte_young(pte)) orig_pte = pte_mkyoung(orig_pte); @@ -227,7 +227,7 @@ pte_t contpte_ptep_get_lockless(pte_t *orig_ptep) goto retry;
if (pte_dirty(pte)) - orig_pte = pte_mkdirty(orig_pte); + orig_pte = __pte_mkdirty(orig_pte);
if (pte_young(pte)) orig_pte = pte_mkyoung(orig_pte); diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index 8251e2fea9c7..678171fd88bd 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -220,7 +220,8 @@ int __ptep_set_access_flags(struct vm_area_struct *vma, return 0;
/* only preserve the access flags and write permission */ - pte_val(entry) &= PTE_RDONLY | PTE_AF | PTE_WRITE | PTE_DIRTY; + pte_val(entry) &= PTE_RDONLY | PTE_AF | PTE_WRITE | + PTE_DIRTY | PTE_SOFT_DIRTY;
/* * Setting the flags must be done atomically to avoid racing with the diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c index 0f0e10bb0a95..4605eb146a2f 100644 --- a/arch/arm64/mm/hugetlbpage.c +++ b/arch/arm64/mm/hugetlbpage.c @@ -155,7 +155,7 @@ pte_t huge_ptep_get(pte_t *ptep) pte_t pte = __ptep_get(ptep);
if (pte_dirty(pte)) - orig_pte = pte_mkdirty(orig_pte); + orig_pte = __pte_mkdirty(orig_pte);
if (pte_young(pte)) orig_pte = pte_mkyoung(orig_pte); @@ -189,7 +189,7 @@ static pte_t get_clear_contig(struct mm_struct *mm, * so check them all. */ if (pte_dirty(pte)) - orig_pte = pte_mkdirty(orig_pte); + orig_pte = __pte_mkdirty(orig_pte);
if (pte_young(pte)) orig_pte = pte_mkyoung(orig_pte); @@ -464,7 +464,7 @@ int huge_ptep_set_access_flags(struct vm_area_struct *vma,
/* Make sure we don't lose the dirty or young state */ if (pte_dirty(orig_pte)) - pte = pte_mkdirty(pte); + pte = __pte_mkdirty(pte);
if (pte_young(orig_pte)) pte = pte_mkyoung(pte); -- 2.25.1