[PATCH] x86/mm/pti: in pti_clone_pgtable() don't increase addr by PUD_SIZE

Song Liu
2019-08-20T07:51:36Z

pti_clone_pgtable() increases addr by PUD_SIZE for pud_none(*pud) case.
This is not accurate because addr may not be PUD_SIZE aligned.

In our x86_64 kernel, pti_clone_pgtable() fails to clone 7 PMDs because
of this issuse, including PMD for the irq entry table. For a memcache
like workload, this introduces about 4.5x more iTLB-load and about 2.5x
more iTLB-load-misses on a Skylake CPU.

This patch fixes this issue by adding PMD_SIZE to addr for pud_none()
case.

Cc: stable@vger.kernel.org # v4.19+
Fixes: 16a3fe634f6a ("x86/mm/pti: Clone kernel-image on PTE level for 32 bit")
Signed-off-by: Song Liu <songliubraving@fb.com>
Cc: Joerg Roedel <jroedel@suse.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
---
arch/x86/mm/pti.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index b196524759ec..5a67c3015f59 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -330,7 +330,7 @@ pti_clone_pgtable(unsigned long start, unsigned long end,

pud = pud_offset(p4d, addr);
if (pud_none(*pud)) {
- addr += PUD_SIZE;
+ addr += PMD_SIZE;
continue;
}

--
2.17.1