linux-kernel - [tip: x86/mm] x86/cpu: Use cpu_feature_enabled() when checking global pages support

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Date:   Wed, 25 Jan 2023 09:43:31 -0000
From:   "tip-bot2 for Borislav Petkov (AMD)" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     "Borislav Petkov (AMD)" <bp@...en8.de>,
        Ingo Molnar <mingo@...nel.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/mm] x86/cpu: Use cpu_feature_enabled() when checking global
 pages support

The following commit has been merged into the x86/mm branch of tip:

Commit-ID:     ebd3ad60a688131de7df1dd05fd2d7c57f542268
Gitweb:        https://git.kernel.org/tip/ebd3ad60a688131de7df1dd05fd2d7c57f542268
Author:        Borislav Petkov (AMD) <bp@...en8.de>
AuthorDate:    Wed, 25 Jan 2023 08:50:13 +01:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Wed, 25 Jan 2023 10:32:06 +01:00

x86/cpu: Use cpu_feature_enabled() when checking global pages support

X86_FEATURE_PGE determines whether the CPU has enabled global page
translations support. Use the faster cpu_feature_enabled() check to
shave off some more cycles when flushing all TLB entries, including the
global ones.

What this practically saves is:

   mov    0x82eb308(%rip),%rax        # 0xffffffff8935bec8 <boot_cpu_data+40>
   test   $0x20,%ah

... which test the bit. Not a lot, but TLB flushing is a timing-sensitive
path, so anything to make it even faster.

No functional changes.

Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Link: https://lore.kernel.org/r/20230125075013.9292-1-bp@alien8.de
---
 arch/x86/mm/tlb.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index c1e31e9..92d73cc 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -1205,7 +1205,7 @@ void __flush_tlb_all(void)
 	 */
 	VM_WARN_ON_ONCE(preemptible());
 
-	if (boot_cpu_has(X86_FEATURE_PGE)) {
+	if (cpu_feature_enabled(X86_FEATURE_PGE)) {
 		__flush_tlb_global();
 	} else {
 		/*