On Thu, Feb 25, 2021, Jing Liu wrote:
> XCOMP_BV[63] field indicates that the save area is in the compacted
> format and XCOMP_BV[62:0] indicates the states that have space allocated
> in the save area, including both XCR0 and XSS bits enabled by the host
> kernel. Use xfeatures_mask_all for calculating xcomp_bv and reuse
> XCOMP_BV_COMPACTED_FORMAT defined by kernel.
>
> Signed-off-by: Jing Liu <jing2.liu@xxxxxxxxxxxxxxx>
> ---
> arch/x86/kvm/x86.c | 8 ++------
> 1 file changed, 2 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 1b404e4d7dd8..f115493f577d 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4435,8 +4435,6 @@ static int kvm_vcpu_ioctl_x86_set_debugregs(struct kvm_vcpu *vcpu,
> return 0;
> }
>
> -#define XSTATE_COMPACTION_ENABLED (1ULL << 63)
> -
> static void fill_xsave(u8 *dest, struct kvm_vcpu *vcpu)
> {
> struct xregs_state *xsave = &vcpu->arch.guest_fpu->state.xsave;
> @@ -4494,7 +4492,8 @@ static void load_xsave(struct kvm_vcpu *vcpu, u8 *src)
> /* Set XSTATE_BV and possibly XCOMP_BV. */
> xsave->header.xfeatures = xstate_bv;
> if (boot_cpu_has(X86_FEATURE_XSAVES))
> - xsave->header.xcomp_bv = host_xcr0 | XSTATE_COMPACTION_ENABLED;
> + xsave->header.xcomp_bv = XCOMP_BV_COMPACTED_FORMAT |
> + xfeatures_mask_all;
Doesn't fill_xsave also need to be updated? Not with xfeatures_mask_all, but
to account for arch.ia32_xss? I believe it's a nop with the current code, since
supported_xss is zero, but it should be fixed, no?
>
> /*
> * Copy each region from the non-compacted offset to the
> @@ -9912,9 +9911,6 @@ static void fx_init(struct kvm_vcpu *vcpu)
> return;
>
> fpstate_init(&vcpu->arch.guest_fpu->state);
> - if (boot_cpu_has(X86_FEATURE_XSAVES))
> - vcpu->arch.guest_fpu->state.xsave.header.xcomp_bv =
> - host_xcr0 | XSTATE_COMPACTION_ENABLED;
Ugh, this _really_ needs a comment in the changelog. It took me a while to
realize fpstate_init() does exactly what the new fill_xave() is doing.
And isn't the code in load_xsave() redundant and can be removed? Any code that
uses get_xsave_addr() would be have a dependency on load_xsave() if it's not
redundant, and I can't see how that would work.
>
> /*
> * Ensure guest xcr0 is valid for loading
> --
> 2.18.4
>
