[PATCH v2] arm64/mm: Hoist synchronization out of set_ptes() loop

* [PATCH v2] arm64/mm: Hoist synchronization out of set_ptes() loop
@ 2023-10-05 14:07 Ryan Roberts
  2023-10-05 14:41 ` Steven Price
                   ` (2 more replies)
  0 siblings, 3 replies; 9+ messages in thread
From: Ryan Roberts @ 2023-10-05 14:07 UTC (permalink / raw)
  To: Catalin Marinas, Will Deacon, Steven Price, Peter Collingbourne
  Cc: Ryan Roberts, linux-arm-kernel, linux-kernel

set_ptes() sets a physically contiguous block of memory (which all
belongs to the same folio) to a contiguous block of ptes. The arm64
implementation of this previously just looped, operating on each
individual pte. But the __sync_icache_dcache() and mte_sync_tags()
operations can both be hoisted out of the loop so that they are
performed once for the contiguous set of pages (which may be less than
the whole folio). This should result in minor performance gains.

__sync_icache_dcache() already acts on the whole folio, and sets a flag
in the folio so that it skips duplicate calls. But by hoisting the call,
all the pte testing is done only once.

mte_sync_tags() operates on each individual page with its own loop. But
by passing the number of pages explicitly, we can rely solely on its
loop and do the checks only once. This approach also makes it robust for
the future, rather than assuming if a head page of a compound page is
being mapped, then the whole compound page is being mapped, instead we
explicitly know how many pages are being mapped. The old assumption may
not continue to hold once the "anonymous large folios" feature is
merged.

Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
---
v2 fixes the invocations of __set_pte_at() to pass nr_pages rather than order.
Thanks to Steven Price for pointing that out.

 arch/arm64/include/asm/mte.h     |  4 ++--
 arch/arm64/include/asm/pgtable.h | 27 +++++++++++++++++----------
 arch/arm64/kernel/mte.c          |  4 ++--
 3 files changed, 21 insertions(+), 14 deletions(-)

diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h
index 4cedbaa16f41..91fbd5c8a391 100644
--- a/arch/arm64/include/asm/mte.h
+++ b/arch/arm64/include/asm/mte.h
@@ -90,7 +90,7 @@ static inline bool try_page_mte_tagging(struct page *page)
 }

 void mte_zero_clear_page_tags(void *addr);
-void mte_sync_tags(pte_t pte);
+void mte_sync_tags(pte_t pte, unsigned int nr_pages);
 void mte_copy_page_tags(void *kto, const void *kfrom);
 void mte_thread_init_user(void);
 void mte_thread_switch(struct task_struct *next);
@@ -122,7 +122,7 @@ static inline bool try_page_mte_tagging(struct page *page)
 static inline void mte_zero_clear_page_tags(void *addr)
 {
 }
-static inline void mte_sync_tags(pte_t pte)
+static inline void mte_sync_tags(pte_t pte, unsigned int nr_pages)
 {
 }
 static inline void mte_copy_page_tags(void *kto, const void *kfrom)
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 7f7d9b1df4e5..68984ba9ce2a 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -325,8 +325,7 @@ static inline void __check_safe_pte_update(struct mm_struct *mm, pte_t *ptep,
 		     __func__, pte_val(old_pte), pte_val(pte));
 }

-static inline void __set_pte_at(struct mm_struct *mm, unsigned long addr,
-				pte_t *ptep, pte_t pte)
+static inline void __sync_cache_and_tags(pte_t pte, unsigned int nr_pages)
 {
 	if (pte_present(pte) && pte_user_exec(pte) && !pte_special(pte))
 		__sync_icache_dcache(pte);
@@ -339,20 +338,18 @@ 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_tagged(pte))
-		mte_sync_tags(pte);
-
-	__check_safe_pte_update(mm, ptep, pte);
-
-	set_pte(ptep, pte);
+		mte_sync_tags(pte, nr_pages);
 }

 static inline void set_ptes(struct mm_struct *mm, unsigned long addr,
 			      pte_t *ptep, pte_t pte, unsigned int nr)
 {
 	page_table_check_ptes_set(mm, ptep, pte, nr);
+	__sync_cache_and_tags(pte, nr);

 	for (;;) {
-		__set_pte_at(mm, addr, ptep, pte);
+		__check_safe_pte_update(mm, ptep, pte);
+		set_pte(ptep, pte);
 		if (--nr == 0)
 			break;
 		ptep++;
@@ -531,18 +528,28 @@ static inline pmd_t pmd_mkdevmap(pmd_t pmd)
 #define pud_pfn(pud)		((__pud_to_phys(pud) & PUD_MASK) >> PAGE_SHIFT)
 #define pfn_pud(pfn,prot)	__pud(__phys_to_pud_val((phys_addr_t)(pfn) << PAGE_SHIFT) | pgprot_val(prot))

+static inline void __set_pte_at(struct mm_struct *mm, unsigned long addr,
+				pte_t *ptep, pte_t pte, unsigned int nr)
+{
+	__sync_cache_and_tags(pte, nr);
+	__check_safe_pte_update(mm, ptep, pte);
+	set_pte(ptep, pte);
+}
+
 static inline void set_pmd_at(struct mm_struct *mm, unsigned long addr,
 			      pmd_t *pmdp, pmd_t pmd)
 {
 	page_table_check_pmd_set(mm, pmdp, pmd);
-	return __set_pte_at(mm, addr, (pte_t *)pmdp, pmd_pte(pmd));
+	return __set_pte_at(mm, addr, (pte_t *)pmdp, pmd_pte(pmd),
+						PMD_SIZE >> PAGE_SHIFT);
 }

 static inline void set_pud_at(struct mm_struct *mm, unsigned long addr,
 			      pud_t *pudp, pud_t pud)
 {
 	page_table_check_pud_set(mm, pudp, pud);
-	return __set_pte_at(mm, addr, (pte_t *)pudp, pud_pte(pud));
+	return __set_pte_at(mm, addr, (pte_t *)pudp, pud_pte(pud),
+						PUD_SIZE >> PAGE_SHIFT);
 }

 #define __p4d_to_phys(p4d)	__pte_to_phys(p4d_pte(p4d))
diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
index 4edecaac8f91..2fb5e7a7a4d5 100644
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c
@@ -35,10 +35,10 @@ DEFINE_STATIC_KEY_FALSE(mte_async_or_asymm_mode);
 EXPORT_SYMBOL_GPL(mte_async_or_asymm_mode);
 #endif

-void mte_sync_tags(pte_t pte)
+void mte_sync_tags(pte_t pte, unsigned int nr_pages)
 {
 	struct page *page = pte_page(pte);
-	long i, nr_pages = compound_nr(page);
+	unsigned int i;

 	/* if PG_mte_tagged is set, tags have already been initialised */
 	for (i = 0; i < nr_pages; i++, page++) {
--
2.25.1


^ permalink raw reply related	[flat|nested] 9+ messages in thread