Always intercepting IA32_XFD causes non-negligible overhead when this
register is updated frequently in the guest.
Disable r/w emulation after intercepting the first WRMSR(IA32_XFD)
with a non-zero value.
Disable WRMSR emulation implies that IA32_XFD becomes out-of-sync
with the software states in fpstate and the per-cpu xfd cache. Call
fpu_sync_guest_vmexit_xfd_state() to bring them back in-sync, before
preemption is enabled.
p.s. We have confirmed that SDM is being revised to say that
when setting IA32_XFD[18] the AMX register state is not guaranteed
to be preserved. This clarification avoids adding mess for a creative
guest which sets IA32_XFD[18]=1 before saving active AMX state to
its own storage.
Signed-off-by: Kevin Tian <kevin.tian@xxxxxxxxx>
Signed-off-by: Yang Zhong <yang.zhong@xxxxxxxxx>
Signed-off-by: Jing Liu <jing2.liu@xxxxxxxxx>
---
arch/x86/include/asm/kvm-x86-ops.h | 1 +
arch/x86/include/asm/kvm_host.h | 2 ++
arch/x86/kvm/vmx/vmx.c | 10 ++++++++++
arch/x86/kvm/vmx/vmx.h | 2 +-
arch/x86/kvm/x86.c | 6 ++++++
5 files changed, 20 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
index cefe1d81e2e8..60c27f9990e9 100644
--- a/arch/x86/include/asm/kvm-x86-ops.h
+++ b/arch/x86/include/asm/kvm-x86-ops.h
@@ -30,6 +30,7 @@ KVM_X86_OP(update_exception_bitmap)
KVM_X86_OP(get_msr)
KVM_X86_OP(set_msr)
KVM_X86_OP(get_segment_base)
+KVM_X86_OP_NULL(set_xfd_passthrough)
KVM_X86_OP(get_segment)
KVM_X86_OP(get_cpl)
KVM_X86_OP(set_segment)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 860ed500580c..b513c12fa39e 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -640,6 +640,7 @@ struct kvm_vcpu_arch {
u64 smi_count;
bool tpr_access_reporting;
bool xsaves_enabled;
+ bool xfd_out_of_sync;
u64 ia32_xss;
u64 microcode_version;
u64 arch_capabilities;
@@ -1329,6 +1330,7 @@ struct kvm_x86_ops {
void (*update_exception_bitmap)(struct kvm_vcpu *vcpu);
int (*get_msr)(struct kvm_vcpu *vcpu, struct msr_data *msr);
int (*set_msr)(struct kvm_vcpu *vcpu, struct msr_data *msr);
+ void (*set_xfd_passthrough)(struct kvm_vcpu *vcpu);
u64 (*get_segment_base)(struct kvm_vcpu *vcpu, int seg);
void (*get_segment)(struct kvm_vcpu *vcpu,
struct kvm_segment *var, int seg);
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 483075045253..97a823a3f23f 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -162,6 +162,7 @@ static u32 vmx_possible_passthrough_msrs[MAX_POSSIBLE_PASSTHROUGH_MSRS] = {
MSR_FS_BASE,
MSR_GS_BASE,
MSR_KERNEL_GS_BASE,
+ MSR_IA32_XFD,
#endif
MSR_IA32_SYSENTER_CS,
MSR_IA32_SYSENTER_ESP,
@@ -1929,6 +1930,14 @@ static u64 vcpu_supported_debugctl(struct kvm_vcpu *vcpu)
return debugctl;
}
+#ifdef CONFIG_X86_64
+static void vmx_set_xfd_passthrough(struct kvm_vcpu *vcpu)
+{
+ vmx_disable_intercept_for_msr(vcpu, MSR_IA32_XFD, MSR_TYPE_RW);
+ vcpu->arch.xfd_out_of_sync = true;
+}
+#endif
+
/*
* Writes msr value into the appropriate "register".
* Returns 0 on success, non-0 otherwise.
@@ -7664,6 +7673,7 @@ static struct kvm_x86_ops vmx_x86_ops __initdata = {
#ifdef CONFIG_X86_64
.set_hv_timer = vmx_set_hv_timer,
.cancel_hv_timer = vmx_cancel_hv_timer,
+ .set_xfd_passthrough = vmx_set_xfd_passthrough,
#endif
.setup_mce = vmx_setup_mce,
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index 4df2ac24ffc1..bf9d3051cd6c 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -340,7 +340,7 @@ struct vcpu_vmx {
struct lbr_desc lbr_desc;
/* Save desired MSR intercept (read: pass-through) state */
-#define MAX_POSSIBLE_PASSTHROUGH_MSRS 13
+#define MAX_POSSIBLE_PASSTHROUGH_MSRS 14
struct {
DECLARE_BITMAP(read, MAX_POSSIBLE_PASSTHROUGH_MSRS);
DECLARE_BITMAP(write, MAX_POSSIBLE_PASSTHROUGH_MSRS);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 796a9f2d1f23..13ba1e066b55 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3686,6 +3686,9 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
return 1;
fpu_update_guest_xfd(&vcpu->arch.guest_fpu, data);
+
+ if (data && kvm_x86_ops.set_xfd_passthrough)
+ static_call(kvm_x86_set_xfd_passthrough)(vcpu);
break;
case MSR_IA32_XFD_ERR:
if (!msr_info->host_initiated &&
@@ -10023,6 +10026,9 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
if (vcpu->arch.guest_fpu.xfd_err)
wrmsrl(MSR_IA32_XFD_ERR, 0);
+ if (vcpu->arch.xfd_out_of_sync)
+ fpu_sync_guest_vmexit_xfd_state();
+
/*
* Consume any pending interrupts, including the possible source of
* VM-Exit on SVM and any ticks that occur between VM-Exit and now.
--
2.27.0
