Re: [PATCH v2] KVM: x86: Revise guest_fpu xcomp_bv field
From: Sean Christopherson <seanjc@google.com>
Date: 2021-03-02 07:44:45
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On Thu, Feb 25, 2021, Jing Liu wrote:
quoted hunk ↗ jump to hunk
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 <redacted> --- 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?
quoted hunk ↗ jump to hunk
/* * 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