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@xxxxxxxxxx>
---
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
