[RFC PATCH 1/2] x86/mm/tlb: Skip batch->cpumask updates when X86_FEATURE_INVLPGB is enabled

[Bing Jiao]

Commit 72a920eacd8a ("x86/mm: Use broadcast TLB flushing in page reclaim")
and commit 0b7eb55cb706 ("x86/mm: Only do broadcast flush from reclaim if
pages were unmapped") changed arch_tlbbatch_flush() to flush all
non-global TLB entries via invlpgb_flush_all_nonglobals() when
X86_FEATURE_INVLPGB is enabled.

However, arch_tlbbatch_add_pending() still unconditionally ORs
mm_cpumask(mm) into batch->cpumask on every unmapped page even when
X86_FEATURE_INVLPGB is enabled.

Guard the batch->cpumask update in arch_tlbbatch_add_pending() with
!cpu_feature_enabled(X86_FEATURE_INVLPGB) to avoid unnecessary bitmap
operations on every unmapped page.

Signed-off-by: Bing Jiao <bingjiao@xxxxxxxxxx>
---
 arch/x86/include/asm/tlbflush.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
index 70098d448e99..4ec71ea0943f 100644
--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -379,7 +379,8 @@ static inline void arch_tlbbatch_add_pending(struct arch_tlbflush_unmap_batch *b
 		struct mm_struct *mm, unsigned long start, unsigned long end)
 {
 	inc_mm_tlb_gen(mm);
-	cpumask_or(&batch->cpumask, &batch->cpumask, mm_cpumask(mm));
+	if (!cpu_feature_enabled(X86_FEATURE_INVLPGB))
+		cpumask_or(&batch->cpumask, &batch->cpumask, mm_cpumask(mm));
 	batch->unmapped_pages = true;
 	mmu_notifier_arch_invalidate_secondary_tlbs(mm, 0, -1UL);
 }
-- 
2.56.0.385.gac671c819a-goog