Re: [PATCH v2 00/66] KVM: x86: Introduce KVM cpu caps

[Sean Christopherson <sean.j.christopherson@xxxxxxxxx>]

On Fri, Mar 06, 2020 at 09:27:48AM +0100, Paolo Bonzini wrote:
> I put the complete series on the cpu-caps branch of kvm.git.

Looks good, arrived at more or less the same end result when rebasing my
local branch to kvm/queue.  CPUID diff and smoke test on Icelake ran clean.

For supported_xss, would it make sense to handle it purely in common x86
code, e.g. stub in something similar to supported_xcr0?  KVM_SUPPORTED_XSS
would be 0 for now.  I assume whatever XSAVES features are supported will
be "supported" by both VMX and SVM, in the sense that VMX/SVM won't need
to mask off features that can exist on their respective hardware but can't
be exposed to the guest.

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 4dca3579e740..c6e9910d1149 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1371,8 +1371,6 @@ static __init void svm_set_cpu_caps(void)
 {
        kvm_set_cpu_caps();
 
-       supported_xss = 0;
-
        /* CPUID 0x80000001 and 0x8000000A (SVM features) */
        if (nested) {
                kvm_cpu_cap_set(X86_FEATURE_SVM);
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 8001070b209c..e91a84bb251c 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7126,7 +7126,6 @@ static __init void vmx_set_cpu_caps(void)
                kvm_cpu_cap_set(X86_FEATURE_UMIP);
 
        /* CPUID 0xD.1 */
-       supported_xss = 0;
        if (!vmx_xsaves_supported())
                kvm_cpu_cap_clear(X86_FEATURE_XSAVES);
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 96e897d38a63..29cfe80db4b4 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9628,6 +9628,8 @@ int kvm_arch_hardware_setup(void)
 
        if (!kvm_cpu_cap_has(X86_FEATURE_XSAVES))
                supported_xss = 0;
+       else
+               supported_xss = host_xss & KVM_SUPPORTED_XSS;
 
        cr4_reserved_bits = kvm_host_cr4_reserved_bits(&boot_cpu_data);