From: Sean Christopherson <seanjc@google.com>
To: Yosry Ahmed <yosry.ahmed@linux.dev>
Cc: x86@kernel.org, Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Peter Zijlstra <peterz@infradead.org>,
Josh Poimboeuf <jpoimboe@kernel.org>,
Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
Andy Lutomirski <luto@kernel.org>,
Paolo Bonzini <pbonzini@redhat.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/6] x86/bugs: Move the X86_FEATURE_USE_IBPB check into callers
Date: Tue, 25 Feb 2025 11:47:53 -0800 [thread overview]
Message-ID: <Z74eaeYm_EgHbmNn@google.com> (raw)
In-Reply-To: <20250219220826.2453186-2-yosry.ahmed@linux.dev>
On Wed, Feb 19, 2025, Yosry Ahmed wrote:
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 6c56d5235f0f3..729a8ee24037b 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -1478,7 +1478,8 @@ void vmx_vcpu_load_vmcs(struct kvm_vcpu *vcpu, int cpu,
> * may switch the active VMCS multiple times).
> */
> if (!buddy || WARN_ON_ONCE(buddy->vmcs != prev))
> - indirect_branch_prediction_barrier();
> + if (cpu_feature_enabled(X86_FEATURE_USE_IBPB))
Combine this into a single if-statement, to make it readable and because as-is
the outer if would need curly braces.
And since this check will stay around in the form of a static_branch, I vote to
check it first so that the checks on "buddy" are elided if vcpu_load_ibpb is disabled.
That'll mean the WARN_ON_ONCE() won't fire if we have a bug and someone is running
with mitigations disabled, but I'm a-ok with that.
next prev parent reply other threads:[~2025-02-25 19:47 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-02-19 22:08 [PATCH 0/6] IBPB cleanups and a fixup Yosry Ahmed
2025-02-19 22:08 ` [PATCH 1/6] x86/bugs: Move the X86_FEATURE_USE_IBPB check into callers Yosry Ahmed
2025-02-25 19:47 ` Sean Christopherson [this message]
2025-02-25 21:28 ` Yosry Ahmed
2025-02-19 22:08 ` [PATCH 2/6] x86/mm: Remove X86_FEATURE_USE_IBPB checks in cond_mitigation() Yosry Ahmed
2025-02-19 22:08 ` [PATCH 3/6] x86/bugs: Remove the X86_FEATURE_USE_IBPB check in ib_prctl_set() Yosry Ahmed
2025-02-19 22:08 ` [PATCH 4/6] x86/bugs: Use a static branch to guard IBPB on vCPU load Yosry Ahmed
2025-02-25 19:49 ` Sean Christopherson
2025-02-25 21:27 ` Yosry Ahmed
2025-02-25 22:40 ` Sean Christopherson
2025-02-26 2:49 ` Yosry Ahmed
2025-02-27 0:46 ` Sean Christopherson
2025-02-27 0:54 ` Yosry Ahmed
2025-02-19 22:08 ` [PATCH 5/6] KVM: nVMX: Always use IBPB to properly virtualize IBRS Yosry Ahmed
2025-02-19 23:09 ` Jim Mattson
2025-02-25 19:50 ` Sean Christopherson
2025-02-19 22:08 ` [PATCH 6/6] x86/bugs: Remove X86_FEATURE_USE_IBPB Yosry Ahmed
2025-02-20 19:04 ` [PATCH 0/6] IBPB cleanups and a fixup Josh Poimboeuf
2025-02-20 19:59 ` Yosry Ahmed
2025-02-20 20:47 ` Josh Poimboeuf
2025-02-20 21:50 ` Yosry Ahmed
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