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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <20230125075013.9292-1-bp@alien8.de>
Date:   Wed, 25 Jan 2023 08:50:13 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     X86 ML <x86@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] x86/cpu: Use cpu_feature_enabled() when checking global pages support

From: "Borislav Petkov (AMD)" <bp@...en8.de>

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>
---
 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 c1e31e9a85d7..92d73ccede70 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 {
 		/*
-- 
2.35.1