linux-kernel - Re: [PATCH 7/8] x86/svm: Set IBPB when running a different VCPU

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Date:   Tue, 9 Jan 2018 09:23:42 -0500
From:   Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        rkrcmar@...hat.com, liran.alon@...cle.com, jmattson@...gle.com,
        aliguori@...zon.com, thomas.lendacky@....com, dwmw@...zon.co.uk,
        bp@...en8.de, x86@...nel.org
Subject: Re: [PATCH 7/8] x86/svm: Set IBPB when running a different VCPU

On Tue, Jan 09, 2018 at 01:03:09PM +0100, Paolo Bonzini wrote:
> From: Tom Lendacky <thomas.lendacky@....com>
> 
> Set IBPB (Indirect Branch Prediction Barrier) when the current CPU is
> going to run a VCPU different from what was previously run.  Nested
> virtualization uses the same VMCB for the second level guest, but the
> L1 hypervisor should be using IBRS to protect itself.
> 
> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/kvm/svm.c | 31 +++++++++++++++++++++++++++++++
>  1 file changed, 31 insertions(+)
> 
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 934a21e02e03..97126c2bd663 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -289,6 +289,7 @@ struct amd_svm_iommu_ir {
>  module_param(vgif, int, 0444);
>   
>  static bool __read_mostly have_spec_ctrl;
> +static bool __read_mostly have_ibpb_support;
>  
>  static void svm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0);
>  static void svm_flush_tlb(struct kvm_vcpu *vcpu, bool invalidate_gpa);
> @@ -540,6 +541,7 @@ struct svm_cpu_data {
>  	struct kvm_ldttss_desc *tss_desc;
>  
>  	struct page *save_area;
> +	struct vmcb *current_vmcb;
>  };
>  
>  static DEFINE_PER_CPU(struct svm_cpu_data *, svm_data);
> @@ -1151,6 +1153,11 @@ static __init int svm_hardware_setup(void)
>  		pr_info("kvm: SPEC_CTRL available\n");
>  	else
>  		pr_info("kvm: SPEC_CTRL not available\n");
> +	have_ibpb_support = have_spec_ctrl || cpu_has_ibpb_support();
> +	if (have_ibpb_support)
> +		pr_info("kvm: IBPB_SUPPORT available\n");
> +	else
> +		pr_info("kvm: IBPB_SUPPORT not available\n");

pr_info("kvm: IBPB_SUPPORT %s available" .. you know :-)