public inbox for linux-kernel@vger.kernel.org
 help / color / mirror / Atom feed
From: Borislav Petkov <bp@alien8.de>
To: X86 ML <x86@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>
Subject: [PATCH] x86/cpu: Use cpu_feature_enabled() when checking global pages support
Date: Wed, 25 Jan 2023 08:50:13 +0100	[thread overview]
Message-ID: <20230125075013.9292-1-bp@alien8.de> (raw)

From: "Borislav Petkov (AMD)" <bp@alien8.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@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 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


             reply	other threads:[~2023-01-25  7:50 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-01-25  7:50 Borislav Petkov [this message]
2023-01-25  9:43 ` [tip: x86/mm] x86/cpu: Use cpu_feature_enabled() when checking global pages support tip-bot2 for Borislav Petkov (AMD)

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20230125075013.9292-1-bp@alien8.de \
    --to=bp@alien8.de \
    --cc=linux-kernel@vger.kernel.org \
    --cc=x86@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox