On Fri, Jan 21, 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. The kvm_set_msr_common()'s handling of MSR_IA32_XSS
> also needs to update kvm_update_cpuid_runtime(). In the above cases, the
> size in bytes of the XSAVE area containing all states enabled by XCR0 or
> (XCRO | IA32_XSS) needs to be updated.
>
> For simplicity and consistency, legacy helpers are used to write values
s/legacy/existing
"legacy" refers to something that is outdated/deprecated, which isn't what you
intend here.
> and call kvm_update_cpuid_runtime(), and it's not exactly a fast path.
>
> Fixes: a554d207dc46 ("KVM: X86: Processor States following Reset or INIT")
> Signed-off-by: Like Xu <likexu@xxxxxxxxxxx>
> ---
> v1 -> v2 Changelog:
> - Strongly prefer that use the helpers to write the values; (Sean)
> - Postpone IA32_XSS test cases once non-zero values are supported; (Paolo)
> - User space may call SET_CPUID2 after kvm_vcpu_reset(init_event=false); (Paolo)
>
> arch/x86/kvm/x86.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> 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);
This relies on a prep patch to invoke kvm_update_cpuid_runtime() in kvm_set_msr_common()
for MSR_IA32_XSS, no?
> static_call(kvm_x86_vcpu_reset)(vcpu, init_event);
>
> --
> 2.33.1
>
>
