On 19/1/2022 2:30 am, Sean Christopherson wrote:
On Mon, Jan 17, 2022, Like Xu wrote:
From: Like Xu <likexu@xxxxxxxxxxx>
XCR0 is reset to 1 by RESET but not INIT and IA32_XSS is zeroed by
both RESET and INIT. In both cases, the size in bytes of the XSAVE
area containing all states enabled by XCR0 or (XCRO | IA32_XSS)
needs to be updated.
Fixes: a554d207dc46 ("KVM: X86: Processor States following Reset or INIT")
Signed-off-by: Like Xu <likexu@xxxxxxxxxxx>
---
arch/x86/kvm/x86.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 76b4803dd3bd..5748a57e1cb7 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11134,6 +11134,7 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
struct kvm_cpuid_entry2 *cpuid_0x1;
unsigned long old_cr0 = kvm_read_cr0(vcpu);
unsigned long new_cr0;
+ bool need_update_cpuid = false;
/*
* Several of the "set" flows, e.g. ->set_cr0(), read other registers
@@ -11199,6 +11200,8 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
vcpu->arch.msr_misc_features_enables = 0;
+ if (vcpu->arch.xcr0 != XFEATURE_MASK_FP)
+ need_update_cpuid = true;
vcpu->arch.xcr0 = XFEATURE_MASK_FP;
}
@@ -11216,6 +11219,8 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
cpuid_0x1 = kvm_find_cpuid_entry(vcpu, 1, 0);
kvm_rdx_write(vcpu, cpuid_0x1 ? cpuid_0x1->eax : 0x600);
+ if (vcpu->arch.ia32_xss)
+ need_update_cpuid = true;
This means that kvm_set_msr_common()'s handling of MSR_IA32_XSS also needs to
update kvm_update_cpuid_runtime(). And then for bnoth XCR0 and XSS, I would very
strongly prefer that use the helpers to write the values and let the helpers call
Looks good to me and let me apply it in the next version.
kvm_update_cpuid_runtime(). Yes, that will mean kvm_update_cpuid_runtime() may be
called multiple times during INIT, but that's already true (CR4), and this isn't
exactly a fast path.
An undisclosed lazy mechanism is under analyzed for performance gains.
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 55518b7d3b96..22d4b1d15e94 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11256,7 +11256,7 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
vcpu->arch.msr_misc_features_enables = 0;
- vcpu->arch.xcr0 = XFEATURE_MASK_FP;
+ __kvm_set_xcr(vcpu, 0, XFEATURE_MASK_FP);
}
/* All GPRs except RDX (handled below) are zeroed on RESET/INIT. */
@@ -11273,7 +11273,7 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
cpuid_0x1 = kvm_find_cpuid_entry(vcpu, 1, 0);
kvm_rdx_write(vcpu, cpuid_0x1 ? cpuid_0x1->eax : 0x600);
- vcpu->arch.ia32_xss = 0;
+ __kvm_set_msr(vcpu, MSR_IA32_XSS, 0, true);
static_call(kvm_x86_vcpu_reset)(vcpu, init_event);
