On Mon, Mar 11, 2019 at 12:12:28PM +0000, Mark Rutland wrote:

Hi,

On Sat, Mar 09, 2019 at 06:19:06PM -0700, Yu Zhao wrote:

quoted

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.

We only do so when pmd is not folded, so we don't mistakenly call
pgtable_pmd_page_ctor() on pud or p4d in pgd_pgtable_alloc(). (We
check shift against PMD_SHIFT, which is same as PUD_SHIFT when pmd
is folded).

Just to check, I take it pgtable_pmd_page_ctor() is now a NOP when the
PMD is folded, and this last paragraph is stale?

Yes, and will remove it.

quoted

Signed-off-by: Yu Zhao <redacted>
---
 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 cfbf307d6dc4..a3b1b789f766 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);
 }

It looks like arm64's existing stage-2 code is inconsistent across
alloc/free, and IIUC this change might turn that into a real problem.
Currently we allocate all levels of stage-2 table with
__get_free_page(), but free them with p?d_free(). We always miss the
ctor and always use the dtor.

Other than that, this patch looks fine to me, but I'd feel more
comfortable if we could first fix the stage-2 code to free those stage-2
tables without invoking the dtor.

Anshuman, IIRC you had a patch to fix the stage-2 code to not invoke the
dtors. If so, could you please post that so that we could take it as a
preparatory patch for this series?

Will do.

Thanks,
Mark.

quoted

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
 

-- 
2.21.0.360.g471c308f928-goog

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