On 30/11/20 14:35, Maxim Levitsky wrote:
This quirk reflects the fact that we currently treat MSR_IA32_TSC
and MSR_TSC_ADJUST access by the host (e.g qemu) in a way that is different
compared to an access from the guest.
For host's MSR_IA32_TSC read we currently always return L1 TSC value, and for
host's write we do the tsc synchronization.
For host's MSR_TSC_ADJUST write, we don't make the tsc 'jump' as we should
for this msr.
When the hypervisor uses the new TSC GET/SET state ioctls, all of this is no
longer needed, thus leave this enabled only with a quirk
which the hypervisor can disable.
Suggested-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
This needs to be covered by a variant of the existing selftests testcase
(running the same guest code, but different host code of course).
Paolo
---
arch/x86/include/uapi/asm/kvm.h | 1 +
arch/x86/kvm/x86.c | 19 ++++++++++++++-----
2 files changed, 15 insertions(+), 5 deletions(-)
diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
index 8e76d3701db3f..2a60fc6674164 100644
--- a/arch/x86/include/uapi/asm/kvm.h
+++ b/arch/x86/include/uapi/asm/kvm.h
@@ -404,6 +404,7 @@ struct kvm_sync_regs {
#define KVM_X86_QUIRK_LAPIC_MMIO_HOLE (1 << 2)
#define KVM_X86_QUIRK_OUT_7E_INC_RIP (1 << 3)
#define KVM_X86_QUIRK_MISC_ENABLE_NO_MWAIT (1 << 4)
+#define KVM_X86_QUIRK_TSC_HOST_ACCESS (1 << 5)
#define KVM_STATE_NESTED_FORMAT_VMX 0
#define KVM_STATE_NESTED_FORMAT_SVM 1
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 4f0ae9cb14b8a..46a2111d54840 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3091,7 +3091,8 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
break;
case MSR_IA32_TSC_ADJUST:
if (guest_cpuid_has(vcpu, X86_FEATURE_TSC_ADJUST)) {
- if (!msr_info->host_initiated) {
+ if (!msr_info->host_initiated ||
+ !kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_TSC_HOST_ACCESS)) {
s64 adj = data - vcpu->arch.ia32_tsc_adjust_msr;
adjust_tsc_offset_guest(vcpu, adj);
}
@@ -3118,7 +3119,8 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
vcpu->arch.msr_ia32_power_ctl = data;
break;
case MSR_IA32_TSC:
- if (msr_info->host_initiated) {
+ if (msr_info->host_initiated &&
+ kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_TSC_HOST_ACCESS)) {
kvm_synchronize_tsc(vcpu, data);
} else {
u64 adj = kvm_compute_tsc_offset(vcpu, data) - vcpu->arch.l1_tsc_offset;
@@ -3409,17 +3411,24 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
msr_info->data = vcpu->arch.msr_ia32_power_ctl;
break;
case MSR_IA32_TSC: {
+ u64 tsc_offset;
+
/*
* Intel SDM states that MSR_IA32_TSC read adds the TSC offset
* even when not intercepted. AMD manual doesn't explicitly
* state this but appears to behave the same.
*
- * On userspace reads and writes, however, we unconditionally
+ * On userspace reads and writes, when KVM_X86_QUIRK_SPECIAL_TSC_READ
+ * is present, however, we unconditionally
* return L1's TSC value to ensure backwards-compatible
* behavior for migration.
*/
- u64 tsc_offset = msr_info->host_initiated ? vcpu->arch.l1_tsc_offset :
- vcpu->arch.tsc_offset;
+
+ if (msr_info->host_initiated &&
+ kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_TSC_HOST_ACCESS))
+ tsc_offset = vcpu->arch.l1_tsc_offset;
+ else
+ tsc_offset = vcpu->arch.tsc_offset;
msr_info->data = kvm_scale_tsc(vcpu, rdtsc()) + tsc_offset;
break;
