[PATCH v2 3/3] arm64: mm: enable per pmd page table lock

[Yu Zhao]

Switch from per mm_struct to per pmd page table lock by enabling
ARCH_ENABLE_SPLIT_PMD_PTLOCK. This provides better granularity for
large system.

I'm not sure if there is contention on mm->page_table_lock. Given
the option comes at no cost (apart from initializing more spin
locks), why not enable it now.

Signed-off-by: Yu Zhao <yuz...@google.com>
---
 arch/arm64/Kconfig               |  3 +++
 arch/arm64/include/asm/pgalloc.h | 12 +++++++++++-
 arch/arm64/include/asm/tlb.h     |  5 ++++-
 3 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index a4168d366127..8dbfa49d926c 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -872,6 +872,9 @@ config ARCH_WANT_HUGE_PMD_SHARE
 config ARCH_HAS_CACHE_LINE_SIZE
        def_bool y
 
+config ARCH_ENABLE_SPLIT_PMD_PTLOCK
+       def_bool y if PGTABLE_LEVELS > 2
+
 config SECCOMP
        bool "Enable seccomp to safely compute untrusted bytecode"
        ---help---
diff --git a/arch/arm64/include/asm/pgalloc.h b/arch/arm64/include/asm/pgalloc.h
index 52fa47c73bf0..dabba4b2c61f 100644
--- a/arch/arm64/include/asm/pgalloc.h
+++ b/arch/arm64/include/asm/pgalloc.h
@@ -33,12 +33,22 @@
 
 static inline pmd_t *pmd_alloc_one(struct mm_struct *mm, unsigned long addr)
 {
-       return (pmd_t *)__get_free_page(PGALLOC_GFP);
+       struct page *page;
+
+       page = alloc_page(PGALLOC_GFP);
+       if (!page)
+               return NULL;
+       if (!pgtable_pmd_page_ctor(page)) {
+               __free_page(page);
+               return NULL;
+       }
+       return page_address(page);
 }
 
 static inline void pmd_free(struct mm_struct *mm, pmd_t *pmdp)
 {
        BUG_ON((unsigned long)pmdp & (PAGE_SIZE-1));
+       pgtable_pmd_page_dtor(virt_to_page(pmdp));
        free_page((unsigned long)pmdp);
 }
 
diff --git a/arch/arm64/include/asm/tlb.h b/arch/arm64/include/asm/tlb.h
index 106fdc951b6e..4e3becfed387 100644
--- a/arch/arm64/include/asm/tlb.h
+++ b/arch/arm64/include/asm/tlb.h
@@ -62,7 +62,10 @@ static inline void __pte_free_tlb(struct mmu_gather *tlb, 
pgtable_t pte,
 static inline void __pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmdp,
                                  unsigned long addr)
 {
-       tlb_remove_table(tlb, virt_to_page(pmdp));
+       struct page *page = virt_to_page(pmdp);
+
+       pgtable_pmd_page_dtor(page);
+       tlb_remove_table(tlb, page);
 }
 #endif
 
-- 
2.21.0.rc0.258.g878e2cd30e-goog