Sean Christopherson <seanjc@xxxxxxxxxx> writes:
> Drop code to initialize XCR0 during fx_init(), a.k.a. vCPU creation, as
> XCR0 has been initialized during kvm_vcpu_reset() (for RESET) since
> commit a554d207dc46 ("KVM: X86: Processor States following Reset or INIT").
>
> Back when XCR0 support was added by commit 2acf923e38fb ("KVM: VMX:
> Enable XSAVE/XRSTOR for guest"), KVM didn't differentiate between RESET
> and INIT. Ignoring the fact that calling fx_init() for INIT is obviously
> wrong, e.g. FPU state after INIT is not the same as after RESET, setting
> XCR0 in fx_init() was correct.
>
> Eventually fx_init() got moved to kvm_arch_vcpu_init(), a.k.a. vCPU
> creation (ignore the terrible name) by commit 0ee6a5172573 ("x86/fpu,
> kvm: Simplify fx_init()"). Finally, commit 95a0d01eef7a ("KVM: x86: Move
> all vcpu init code into kvm_arch_vcpu_create()") killed off
> kvm_arch_vcpu_init(),
Technically, empty kvm_arch_vcpu_init() was still alive for a few more
commits and only ddd259c9aaba ("KVM: Drop kvm_arch_vcpu_init() and
kvm_arch_vcpu_uninit()") killed it for real but a curious reader can
find all these gory details himself)
> leaving behind the oddity of redundant setting of
> guest state during vCPU creation.
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
> arch/x86/kvm/x86.c | 7 +------
> 1 file changed, 1 insertion(+), 6 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index e0bff5473813..6fd3fe21863e 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -993,7 +993,7 @@ static int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr)
> /*
> * Do not allow the guest to set bits that we do not support
> * saving. However, xcr0 bit 0 is always set, even if the
> - * emulated CPU does not support XSAVE (see fx_init).
> + * emulated CPU does not support XSAVE (see kvm_vcpu_reset()).
> */
> valid_bits = vcpu->arch.guest_supported_xcr0 | XFEATURE_MASK_FP;
> if (xcr0 & ~valid_bits)
> @@ -10623,11 +10623,6 @@ static void fx_init(struct kvm_vcpu *vcpu)
> if (boot_cpu_has(X86_FEATURE_XSAVES))
> vcpu->arch.guest_fpu->state.xsave.header.xcomp_bv =
> host_xcr0 | XSTATE_COMPACTION_ENABLED;
> -
> - /*
> - * Ensure guest xcr0 is valid for loading
> - */
> - vcpu->arch.xcr0 = XFEATURE_MASK_FP;
> }
>
> void kvm_free_guest_fpu(struct kvm_vcpu *vcpu)
Reviewed-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
--
Vitaly
