From: Sean Christopherson <seanjc@google.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: ubizjak@gmail.com, bp@alien8.de, dave.hansen@linux.intel.com,
hpa@zytor.com, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org, mingo@kernel.org,
pbonzini@redhat.com, tglx@kernel.org, x86@kernel.org
Subject: Re: [PATCH 1/2] KVM: VMX: Drop obsolete branch hint prefixes from inline asm
Date: Wed, 11 Feb 2026 05:36:42 -0800 [thread overview]
Message-ID: <aYyF6sf6IQs47Vxu@google.com> (raw)
In-Reply-To: <2af5e3a8-f520-40fd-96a5-28555c3e4a5e@citrix.com>
On Wed, Feb 11, 2026, Andrew Cooper wrote:
> > Remove explicit branch hint prefixes (.byte 0x2e / 0x3e) from VMX
> > inline assembly sequences.
> >
> > These prefixes (CS/DS segment overrides used as branch hints on
> > very old x86 CPUs) have been ignored by modern processors for a
> > long time. Keeping them provides no measurable benefit and only
> > enlarges the generated code.
>
> It's actually worse than this.
>
> The branch-taken hint has new meaning in Lion Cove cores and later,
> along with a warning saying "performance penalty for misuse".
Well that's just lovely. Sounds like maybe this should be tagged for stable@?
next prev parent reply other threads:[~2026-02-11 13:36 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-02-11 10:28 [PATCH 1/2] KVM: VMX: Drop obsolete branch hint prefixes from inline asm Uros Bizjak
2026-02-11 10:28 ` [PATCH 2/2] KVM: VMX: Use ASM_INPUT_RM in __vmcs_writel Uros Bizjak
2026-02-25 19:02 ` Nathan Chancellor
2026-02-11 10:57 ` [PATCH 1/2] KVM: VMX: Drop obsolete branch hint prefixes from inline asm Andrew Cooper
2026-02-11 13:36 ` Sean Christopherson [this message]
2026-02-11 13:43 ` David Laight
2026-02-11 13:55 ` Andrew Cooper
2026-02-11 15:44 ` Sean Christopherson
2026-02-11 16:11 ` Andrew Cooper
2026-02-11 16:17 ` Sean Christopherson
2026-02-11 16:46 ` Andrew Cooper
2026-02-11 16:49 ` Sean Christopherson
2026-02-11 21:35 ` David Laight
2026-03-05 17:08 ` Sean Christopherson
-- strict thread matches above, loose matches on Subject: below --
2026-02-12 5:33 Christian Ludloff
2026-02-12 16:18 ` Andrew Cooper
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