[PATCH v1 09/14] arm64/mm: ptep_get(): New layer to manage contig bit

From: Ryan Roberts
Date: Thu Jun 22 2023 - 10:43:35 EST

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Create a new layer for the in-table PTE manipulation APIs. For now, The
existing API is prefixed with double underscore to become the
arch-private API and the public API is just a simple wrapper that calls
the private API.

The public API implementation will subsequently be used to transparently
manipulate the contiguous bit where appropriate. But since there are
already some contig-aware users (e.g. hugetlb, kernel mapper), we must
first ensure those users use the private API directly so that the future
contig-bit manipulations in the public API do not interfere with those
existing uses.

arm64 did not previously define an arch-specific ptep_get(), so override
the default version in the arch code, and also define the private
__ptep_get() version. Currently they both do the same thing that the
default version does (READ_ONCE()). Some arch users (hugetlb) were
already using ptep_get() so convert those to the private API. While
other callsites were doing direct READ_ONCE(), so convert those to use
the appropriate (public/private) API too.

There are some core kernel locations that directly dereference the ptep,
so these will need to be updated separately.

No behavioural changes intended.

Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx>
---
arch/arm64/include/asm/pgtable.h | 19 +++++++++++++++----
arch/arm64/kernel/efi.c | 2 +-
arch/arm64/mm/fault.c | 4 ++--
arch/arm64/mm/hugetlbpage.c | 18 +++++++++---------
arch/arm64/mm/kasan_init.c | 2 +-
arch/arm64/mm/mmu.c | 12 ++++++------
arch/arm64/mm/pageattr.c | 4 ++--
arch/arm64/mm/trans_pgd.c | 2 +-
8 files changed, 37 insertions(+), 26 deletions(-)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index ff79578fd806..31df4d73f9ac 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -275,6 +275,11 @@ static inline void __set_pte(pte_t *ptep, pte_t pte)
}
}

+static inline pte_t __ptep_get(pte_t *ptep)
+{
+ return READ_ONCE(*ptep);
+}
+
extern void __sync_icache_dcache(pte_t pteval);
bool pgattr_change_is_safe(u64 old, u64 new);

@@ -302,7 +307,7 @@ static inline void __check_safe_pte_update(struct mm_struct *mm, pte_t *ptep,
if (!IS_ENABLED(CONFIG_DEBUG_VM))
return;

- old_pte = READ_ONCE(*ptep);
+ old_pte = __ptep_get(ptep);

if (!pte_valid(old_pte) || !pte_valid(pte))
return;
@@ -339,7 +344,7 @@ static inline void __set_pte_at(struct mm_struct *mm, unsigned long addr,
*/
if (system_supports_mte() && pte_access_permitted(pte, false) &&
!pte_special(pte)) {
- pte_t old_pte = READ_ONCE(*ptep);
+ pte_t old_pte = __ptep_get(ptep);
/*
* We only need to synchronise if the new PTE has tags enabled
* or if swapping in (in which case another mapping may have
@@ -893,7 +898,7 @@ static inline int __ptep_test_and_clear_young(struct vm_area_struct *vma,
{
pte_t old_pte, pte;

- pte = READ_ONCE(*ptep);
+ pte = __ptep_get(ptep);
do {
old_pte = pte;
pte = pte_mkold(pte);
@@ -966,7 +971,7 @@ static inline void __ptep_set_wrprotect(struct mm_struct *mm,
{
pte_t old_pte, pte;

- pte = READ_ONCE(*ptep);
+ pte = __ptep_get(ptep);
do {
old_pte = pte;
pte = pte_wrprotect(pte);
@@ -1120,6 +1125,12 @@ extern void ptep_modify_prot_commit(struct vm_area_struct *vma,
* private versions, which are prefixed with double underscore.
*/

+#define ptep_get ptep_get
+static inline pte_t ptep_get(pte_t *ptep)
+{
+ return __ptep_get(ptep);
+}
+
static inline void set_pte(pte_t *ptep, pte_t pte)
{
__set_pte(ptep, pte);
diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c
index 7a28b6a08a82..9536fbce77a2 100644
--- a/arch/arm64/kernel/efi.c
+++ b/arch/arm64/kernel/efi.c
@@ -106,7 +106,7 @@ static int __init set_permissions(pte_t *ptep, unsigned long addr, void *data)
{
struct set_perm_data *spd = data;
const efi_memory_desc_t *md = spd->md;
- pte_t pte = READ_ONCE(*ptep);
+ pte_t pte = __ptep_get(ptep);

if (md->attribute & EFI_MEMORY_RO)
pte = set_pte_bit(pte, __pgprot(PTE_RDONLY));
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index f5a7a5ff6814..3193526b226d 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -177,7 +177,7 @@ static void show_pte(unsigned long addr)
break;

ptep = pte_offset_map(pmdp, addr);
- pte = READ_ONCE(*ptep);
+ pte = __ptep_get(ptep);
pr_cont(", pte=%016llx", pte_val(pte));
pte_unmap(ptep);
} while(0);
@@ -200,7 +200,7 @@ int __ptep_set_access_flags(struct vm_area_struct *vma,
pte_t entry, int dirty)
{
pteval_t old_pteval, pteval;
- pte_t pte = READ_ONCE(*ptep);
+ pte_t pte = __ptep_get(ptep);

if (pte_same(pte, entry))
return 0;
diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
index 9a87b1c5661a..82b2036dbe2f 100644
--- a/arch/arm64/mm/hugetlbpage.c
+++ b/arch/arm64/mm/hugetlbpage.c
@@ -152,14 +152,14 @@ pte_t huge_ptep_get(pte_t *ptep)
{
int ncontig, i;
size_t pgsize;
- pte_t orig_pte = ptep_get(ptep);
+ pte_t orig_pte = __ptep_get(ptep);

if (!pte_present(orig_pte) || !pte_cont(orig_pte))
return orig_pte;

ncontig = num_contig_ptes(page_size(pte_page(orig_pte)), &pgsize);
for (i = 0; i < ncontig; i++, ptep++) {
- pte_t pte = ptep_get(ptep);
+ pte_t pte = __ptep_get(ptep);

if (pte_dirty(pte))
orig_pte = pte_mkdirty(orig_pte);
@@ -184,7 +184,7 @@ static pte_t get_clear_contig(struct mm_struct *mm,
unsigned long pgsize,
unsigned long ncontig)
{
- pte_t orig_pte = ptep_get(ptep);
+ pte_t orig_pte = __ptep_get(ptep);
unsigned long i;

for (i = 0; i < ncontig; i++, addr += pgsize, ptep++) {
@@ -426,7 +426,7 @@ pte_t huge_ptep_get_and_clear(struct mm_struct *mm,
{
int ncontig;
size_t pgsize;
- pte_t orig_pte = ptep_get(ptep);
+ pte_t orig_pte = __ptep_get(ptep);

if (!pte_cont(orig_pte))
return __ptep_get_and_clear(mm, addr, ptep);
@@ -449,11 +449,11 @@ static int __cont_access_flags_changed(pte_t *ptep, pte_t pte, int ncontig)
{
int i;

- if (pte_write(pte) != pte_write(ptep_get(ptep)))
+ if (pte_write(pte) != pte_write(__ptep_get(ptep)))
return 1;

for (i = 0; i < ncontig; i++) {
- pte_t orig_pte = ptep_get(ptep + i);
+ pte_t orig_pte = __ptep_get(ptep + i);

if (pte_dirty(pte) != pte_dirty(orig_pte))
return 1;
@@ -510,7 +510,7 @@ void huge_ptep_set_wrprotect(struct mm_struct *mm,
size_t pgsize;
pte_t pte;

- if (!pte_cont(READ_ONCE(*ptep))) {
+ if (!pte_cont(__ptep_get(ptep))) {
__ptep_set_wrprotect(mm, addr, ptep);
return;
}
@@ -535,7 +535,7 @@ pte_t huge_ptep_clear_flush(struct vm_area_struct *vma,
size_t pgsize;
int ncontig;

- if (!pte_cont(READ_ONCE(*ptep)))
+ if (!pte_cont(__ptep_get(ptep)))
return ptep_clear_flush(vma, addr, ptep);

ncontig = find_num_contig(mm, addr, ptep, &pgsize);
@@ -569,7 +569,7 @@ pte_t huge_ptep_modify_prot_start(struct vm_area_struct *vma, unsigned long addr
* when the permission changes from executable to non-executable
* in cases where cpu is affected with errata #2645198.
*/
- if (pte_user_exec(READ_ONCE(*ptep)))
+ if (pte_user_exec(__ptep_get(ptep)))
return huge_ptep_clear_flush(vma, addr, ptep);
}
return huge_ptep_get_and_clear(vma->vm_mm, addr, ptep);
diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
index 40125b217195..65074cf7f3a3 100644
--- a/arch/arm64/mm/kasan_init.c
+++ b/arch/arm64/mm/kasan_init.c
@@ -113,7 +113,7 @@ static void __init kasan_pte_populate(pmd_t *pmdp, unsigned long addr,
memset(__va(page_phys), KASAN_SHADOW_INIT, PAGE_SIZE);
next = addr + PAGE_SIZE;
__set_pte(ptep, pfn_pte(__phys_to_pfn(page_phys), PAGE_KERNEL));
- } while (ptep++, addr = next, addr != end && pte_none(READ_ONCE(*ptep)));
+ } while (ptep++, addr = next, addr != end && pte_none(__ptep_get(ptep)));
}

static void __init kasan_pmd_populate(pud_t *pudp, unsigned long addr,
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 085a7e3eec98..d5dc36ff3827 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -176,7 +176,7 @@ static void init_pte(pmd_t *pmdp, unsigned long addr, unsigned long end,

ptep = pte_set_fixmap_offset(pmdp, addr);
do {
- pte_t old_pte = READ_ONCE(*ptep);
+ pte_t old_pte = __ptep_get(ptep);

__set_pte(ptep, pfn_pte(__phys_to_pfn(phys), prot));

@@ -185,7 +185,7 @@ static void init_pte(pmd_t *pmdp, unsigned long addr, unsigned long end,
* only allow updates to the permission attributes.
*/
BUG_ON(!pgattr_change_is_safe(pte_val(old_pte),
- READ_ONCE(pte_val(*ptep))));
+ pte_val(__ptep_get(ptep))));

phys += PAGE_SIZE;
} while (ptep++, addr += PAGE_SIZE, addr != end);
@@ -848,7 +848,7 @@ static void unmap_hotplug_pte_range(pmd_t *pmdp, unsigned long addr,

do {
ptep = pte_offset_kernel(pmdp, addr);
- pte = READ_ONCE(*ptep);
+ pte = __ptep_get(ptep);
if (pte_none(pte))
continue;

@@ -981,7 +981,7 @@ static void free_empty_pte_table(pmd_t *pmdp, unsigned long addr,

do {
ptep = pte_offset_kernel(pmdp, addr);
- pte = READ_ONCE(*ptep);
+ pte = __ptep_get(ptep);

/*
* This is just a sanity check here which verifies that
@@ -1000,7 +1000,7 @@ static void free_empty_pte_table(pmd_t *pmdp, unsigned long addr,
*/
ptep = pte_offset_kernel(pmdp, 0UL);
for (i = 0; i < PTRS_PER_PTE; i++) {
- if (!pte_none(READ_ONCE(ptep[i])))
+ if (!pte_none(__ptep_get(ptep++)))
return;
}

@@ -1470,7 +1470,7 @@ pte_t ptep_modify_prot_start(struct vm_area_struct *vma, unsigned long addr, pte
* when the permission changes from executable to non-executable
* in cases where cpu is affected with errata #2645198.
*/
- if (pte_user_exec(READ_ONCE(*ptep)))
+ if (pte_user_exec(ptep_get(ptep)))
return ptep_clear_flush(vma, addr, ptep);
}
return ptep_get_and_clear(vma->vm_mm, addr, ptep);
diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index 057097acf9e0..624b0b0982e3 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c
@@ -36,7 +36,7 @@ bool can_set_direct_map(void)
static int change_page_range(pte_t *ptep, unsigned long addr, void *data)
{
struct page_change_data *cdata = data;
- pte_t pte = READ_ONCE(*ptep);
+ pte_t pte = __ptep_get(ptep);

pte = clear_pte_bit(pte, cdata->clear_mask);
pte = set_pte_bit(pte, cdata->set_mask);
@@ -246,5 +246,5 @@ bool kernel_page_present(struct page *page)
return true;

ptep = pte_offset_kernel(pmdp, addr);
- return pte_valid(READ_ONCE(*ptep));
+ return pte_valid(__ptep_get(ptep));
}
diff --git a/arch/arm64/mm/trans_pgd.c b/arch/arm64/mm/trans_pgd.c
index f9997b226614..b130a65092c1 100644
--- a/arch/arm64/mm/trans_pgd.c
+++ b/arch/arm64/mm/trans_pgd.c
@@ -32,7 +32,7 @@ static void *trans_alloc(struct trans_pgd_info *info)

static void _copy_pte(pte_t *dst_ptep, pte_t *src_ptep, unsigned long addr)
{
- pte_t pte = READ_ONCE(*src_ptep);
+ pte_t pte = __ptep_get(src_ptep);

if (pte_valid(pte)) {
/*
--
2.25.1

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