lkml.org 
[lkml]   [2018]   [Jan]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 5/7] kvm: svm: pass MSR_IA32_SPEC_CTRL and MSR_IA32_PRED_CMD down to guest


On 08/01/18 20:08, Paolo Bonzini wrote:
> Direct access to MSR_IA32_SPEC_CTRL and MSR_IA32_PRED_CMD is important
> for performance. Allow load/store of MSR_IA32_SPEC_CTRL, restore guest
> IBRS on VM entry and set it to 0 on VM exit (because Linux does not use
> it yet).
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> arch/x86/kvm/svm.c | 34 +++++++++++++++++++++++++++++++++-
> 1 file changed, 33 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 55dde3896898..779981a00d01 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -183,6 +183,8 @@ struct vcpu_svm {
> u64 gs_base;
> } host;
>
> + u64 spec_ctrl;
> +
> u32 *msrpm;
>
> ulong nmi_iret_rip;
> @@ -236,7 +238,7 @@ struct amd_svm_iommu_ir {
>
> static const struct svm_direct_access_msrs {
> u32 index; /* Index of the MSR */
> - bool always; /* True if intercept is always on */
> + bool always; /* True if intercept is always off */

By examining svm_vcpu_init_msrpm() it seems you are correct as if
always==true then read/write bits are cleared from msrpm (which
pass-through the MSR to the guest).

However, I do think this comment change should be done in a separate
commit as it is unrelated.

> } direct_access_msrs[] = {
> { .index = MSR_STAR, .always = true },
> { .index = MSR_IA32_SYSENTER_CS, .always = true },
> @@ -248,6 +250,8 @@ struct amd_svm_iommu_ir {
> { .index = MSR_CSTAR, .always = true },
> { .index = MSR_SYSCALL_MASK, .always = true },
> #endif
> + { .index = MSR_IA32_SPEC_CTRL, .always = true },
> + { .index = MSR_IA32_PRED_CMD, .always = true },
> { .index = MSR_IA32_LASTBRANCHFROMIP, .always = false },
> { .index = MSR_IA32_LASTBRANCHTOIP, .always = false },
> { .index = MSR_IA32_LASTINTFROMIP, .always = false },
> @@ -283,6 +287,8 @@ struct amd_svm_iommu_ir {
> /* enable/disable Virtual GIF */
> static int vgif = true;
> module_param(vgif, int, 0444);
> +
> +static bool __read_mostly have_spec_ctrl;
>
> static void svm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0);
> static void svm_flush_tlb(struct kvm_vcpu *vcpu, bool invalidate_gpa);
> @@ -1135,6 +1141,17 @@ static __init int svm_hardware_setup(void)
> pr_info("Virtual GIF supported\n");
> }
>
> + /*
> + * FIXME: this is only needed until SPEC_CTRL is supported
> + * by upstream Linux in cpufeatures, then it can be replaced
> + * with static_cpu_has.
> + */
> + have_spec_ctrl = cpu_has_spec_ctrl();
> + if (have_spec_ctrl)
> + pr_info("kvm: SPEC_CTRL available\n");
> + else
> + pr_info("kvm: SPEC_CTRL not available\n");
> +
> return 0;
>
> err:
> @@ -3599,6 +3616,9 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> case MSR_VM_CR:
> msr_info->data = svm->nested.vm_cr_msr;
> break;
> + case MSR_IA32_SPEC_CTRL:
> + msr_info->data = svm->spec_ctrl;
> + break;
> case MSR_IA32_UCODE_REV:
> msr_info->data = 0x01000065;
> break;
> @@ -3754,6 +3774,9 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
> case MSR_VM_IGNNE:
> vcpu_unimpl(vcpu, "unimplemented wrmsr: 0x%x data 0x%llx\n", ecx, data);
> break;
> + case MSR_IA32_SPEC_CTRL:
> + svm->spec_ctrl = data;
> + break;
> case MSR_IA32_APICBASE:
> if (kvm_vcpu_apicv_active(vcpu))
> avic_update_vapic_bar(to_svm(vcpu), data);
> @@ -4942,6 +4965,9 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
>
> local_irq_enable();
>
> + if (have_spec_ctrl && svm->spec_ctrl != 0)
> + wrmsrl(MSR_IA32_SPEC_CTRL, svm->spec_ctrl);
> +
> asm volatile (
> "push %%" _ASM_BP "; \n\t"
> "mov %c[rbx](%[svm]), %%" _ASM_BX " \n\t"
> @@ -5015,6 +5041,12 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
> #endif
> );
>
> + if (have_spec_ctrl) {
> + rdmsrl(MSR_IA32_SPEC_CTRL, svm->spec_ctrl);
> + if (svm->spec_ctrl != 0)

Very small stuff but I hate inconsistencies:
Either you put here (svm->spec_ctrl) like in arch/x86/kvm/vmx.c or you
will use there (vmx->spec_ctrl != 0).

> + wrmsrl(MSR_IA32_SPEC_CTRL, 0);
> + }
> +
> #ifdef CONFIG_X86_64
> wrmsrl(MSR_GS_BASE, svm->host.gs_base);
> #else
>

\
 
 \ /
  Last update: 2018-01-14 23:18    [W:0.503 / U:0.176 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site