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Date: Mon, 22 Jan 2018 10:56:05 -0800
From: Jim Mattson <jmattson@...gle.com>
To: KarimAllah Ahmed <karahmed@...zon.de>
Cc: LKML <linux-kernel@...r.kernel.org>,
Andi Kleen <ak@...ux.intel.com>,
Andrea Arcangeli <aarcange@...hat.com>,
Andy Lutomirski <luto@...nel.org>,
Arjan van de Ven <arjan@...ux.intel.com>,
Ashok Raj <ashok.raj@...el.com>,
Asit Mallick <asit.k.mallick@...el.com>,
Borislav Petkov <bp@...e.de>,
Dan Williams <dan.j.williams@...el.com>,
Dave Hansen <dave.hansen@...el.com>,
David Woodhouse <dwmw@...zon.co.uk>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"H . Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
Janakarajan Natarajan <Janakarajan.Natarajan@....com>,
Joerg Roedel <joro@...tes.org>,
Jun Nakajima <jun.nakajima@...el.com>,
Laura Abbott <labbott@...hat.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
Paolo Bonzini <pbonzini@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Radim Krčmář <rkrcmar@...hat.com>,
Thomas Gleixner <tglx@...utronix.de>,
Tim Chen <tim.c.chen@...ux.intel.com>,
Tom Lendacky <thomas.lendacky@....com>,
kvm list <kvm@...r.kernel.org>,
"the arch/x86 maintainers" <x86@...nel.org>,
Arjan Van De Ven <arjan.van.de.ven@...el.com>
Subject: Re: [RFC 02/10] x86/kvm: Add IBPB support
On Sat, Jan 20, 2018 at 11:22 AM, KarimAllah Ahmed <karahmed@...zon.de> wrote:
> From: Ashok Raj <ashok.raj@...el.com>
>
> Add MSR passthrough for MSR_IA32_PRED_CMD and place branch predictor
> barriers on switching between VMs to avoid inter VM specte-v2 attacks.
>
> [peterz: rebase and changelog rewrite]
> [dwmw2: fixes]
> [karahmed: - vmx: expose PRED_CMD whenever it is available
> - svm: only pass through IBPB if it is available]
>
> Cc: Asit Mallick <asit.k.mallick@...el.com>
> Cc: Dave Hansen <dave.hansen@...el.com>
> Cc: Arjan Van De Ven <arjan.van.de.ven@...el.com>
> Cc: Tim Chen <tim.c.chen@...ux.intel.com>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Andrea Arcangeli <aarcange@...hat.com>
> Cc: Andi Kleen <ak@...ux.intel.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Jun Nakajima <jun.nakajima@...el.com>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Greg KH <gregkh@...uxfoundation.org>
> Cc: David Woodhouse <dwmw@...zon.co.uk>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Signed-off-by: Ashok Raj <ashok.raj@...el.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Link: http://lkml.kernel.org/r/1515720739-43819-6-git-send-email-ashok.raj@intel.com
>
> Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
> Signed-off-by: KarimAllah Ahmed <karahmed@...zon.de>
> ---
> arch/x86/kvm/svm.c | 14 ++++++++++++++
> arch/x86/kvm/vmx.c | 4 ++++
> 2 files changed, 18 insertions(+)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 2744b973..cfdb9ab 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -529,6 +529,7 @@ 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);
> @@ -918,6 +919,9 @@ static void svm_vcpu_init_msrpm(u32 *msrpm)
>
> set_msr_interception(msrpm, direct_access_msrs[i].index, 1, 1);
> }
> +
> + if (boot_cpu_has(X86_FEATURE_AMD_PRED_CMD))
> + set_msr_interception(msrpm, MSR_IA32_PRED_CMD, 1, 1);
> }
>
> static void add_msr_offset(u32 offset)
> @@ -1706,11 +1710,17 @@ 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 page can be recycled, causing a false negative in
> + * svm_vcpu_load(). So do a full IBPB now.
> + */
> + indirect_branch_prediction_barrier();
> }
>
> static void svm_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
> {
> struct vcpu_svm *svm = to_svm(vcpu);
> + struct svm_cpu_data *sd = per_cpu(svm_data, cpu);
> int i;
>
> if (unlikely(cpu != vcpu->cpu)) {
> @@ -1739,6 +1749,10 @@ static void svm_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
> if (static_cpu_has(X86_FEATURE_RDTSCP))
> wrmsrl(MSR_TSC_AUX, svm->tsc_aux);
>
> + if (sd->current_vmcb != svm->vmcb) {
> + sd->current_vmcb = svm->vmcb;
> + indirect_branch_prediction_barrier();
> + }
> avic_vcpu_load(vcpu, cpu);
> }
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index d1e25db..3b64de2 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -2279,6 +2279,7 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
> if (per_cpu(current_vmcs, cpu) != vmx->loaded_vmcs->vmcs) {
> per_cpu(current_vmcs, cpu) = vmx->loaded_vmcs->vmcs;
> vmcs_load(vmx->loaded_vmcs->vmcs);
> + indirect_branch_prediction_barrier();
> }
>
> if (!already_loaded) {
> @@ -6791,6 +6792,9 @@ static __init int hardware_setup(void)
> kvm_tsc_scaling_ratio_frac_bits = 48;
> }
>
> + if (boot_cpu_has(X86_FEATURE_SPEC_CTRL))
I think the condition here should be:
if (guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL))
__do_cpuid_ent should pass through X86_FEATURE_SPEC_CTRL from the
host, but userspace should be allowed to clear it.
(Userspace should not be allowed to set it if the host doesn't support it.)
> + vmx_disable_intercept_for_msr(MSR_IA32_PRED_CMD, false);
> +
> vmx_disable_intercept_for_msr(MSR_FS_BASE, false);
> vmx_disable_intercept_for_msr(MSR_GS_BASE, false);
> vmx_disable_intercept_for_msr(MSR_KERNEL_GS_BASE, true);
> --
> 2.7.4
>
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