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Date: Fri, 12 Jan 2018 11:08:18 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Ashok Raj <ashok.raj@intel.com>
Cc: linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
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        Dave Hansen <dave.hansen@intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andi Kleen <ak@linux.intel.com>,
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        David Woodhouse <dwmw@amazon.co.uk>,
        Dan Williams <dan.j.williams@intel.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Jun Nakajima <jun.nakajima@intel.com>,
        Asit Mallick <asit.k.mallick@intel.com>
Subject: Re: [PATCH 5/5] x86/feature: Detect the x86 feature Indirect Branch
 Prediction Barrier
Message-ID: <20180112100817.GR3040@hirez.programming.kicks-ass.net>
References: <1515720739-43819-1-git-send-email-ashok.raj@intel.com>
 <1515720739-43819-6-git-send-email-ashok.raj@intel.com>
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On Thu, Jan 11, 2018 at 05:32:19PM -0800, Ashok Raj wrote:
> @@ -1711,11 +1715,18 @@ static void svm_free_vcpu(struct kvm_vcpu *vcpu)
>  	__free_pages(virt_to_page(svm->nested.msrpm), MSRPM_ALLOC_ORDER);
>  	kvm_vcpu_uninit(vcpu);
>  	kmem_cache_free(kvm_vcpu_cache, svm);
> +    /* 
> +     * The VMCB could be recycled, causing a false negative in svm_vcpu_load;
> +     * block speculative execution.
> +     */
> +	if (boot_cpu_has(X86_FEATURE_PRED_CMD))
> +        native_wrmsrl(MSR_IA32_PRED_CMD, FEATURE_SET_IBPB);
>  }

> @@ -3837,6 +3839,12 @@ static void free_loaded_vmcs(struct loaded_vmcs *loaded_vmcs)
>  	free_vmcs(loaded_vmcs->vmcs);
>  	loaded_vmcs->vmcs = NULL;
>  	WARN_ON(loaded_vmcs->shadow_vmcs != NULL);
> +    /*
> +     * The VMCS could be recycled, causing a false negative in vmx_vcpu_load
> +     * block speculative execution.
> +     */
> +	if (boot_cpu_has(X86_FEATURE_SPEC_CTRL))
> +        native_wrmsrl(MSR_IA32_PRED_CMD, FEATURE_SET_IBPB);
>  }

Whitespace damage.

Also, why not introduce a helper like:

static inline flush_ibpb(void)
{
	if (static_cpu_has(X86_FEATURE_SPEC_CTRL))
		native_write_msr(MSR_IA32_PRED_CMD, FEATURE_SET_IBPB);
}

?