Messages in this thread |  | | Subject | Re: [PATCH RFC 7/7] kvm: x86: AMX XCR0 support for guest | From | "Liu, Jing2" <> | Date | Wed, 26 May 2021 15:54:23 +0800 |
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On 5/25/2021 5:53 AM, Sean Christopherson wrote: > On Sun, Feb 07, 2021, Jing Liu wrote: >> Two XCR0 bits are defined for AMX to support XSAVE mechanism. >> Bit 17 is for tilecfg and bit 18 is for tiledata. > This fails to explain why they must be set in tandem. The spec says, "executing the XSETBV instruction causes a general-protection fault (#GP) if ECX=0 and EAX[17] ≠ EAX[18] (XTILECFG and XTILEDATA must be enabled together). This implies that the value of XCR0[17:18] is always either 00b or 11b."
I can add more to changelog if this is reasonable. > Out of curisoity, assuming > they do indeed need to be set/cleared as a pair, what's the point of having two > separate bits? What I can see is to separate different states and mirror by XFD which can set bits separately.
Thanks, Jing
> >> Signed-off-by: Jing Liu <jing2.liu@linux.intel.com> >> --- >> arch/x86/kvm/x86.c | 8 +++++++- >> 1 file changed, 7 insertions(+), 1 deletion(-) >> >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >> index bfbde877221e..f1c5893dee18 100644 >> --- a/arch/x86/kvm/x86.c >> +++ b/arch/x86/kvm/x86.c >> @@ -189,7 +189,7 @@ static struct kvm_user_return_msrs __percpu *user_return_msrs; >> #define KVM_SUPPORTED_XCR0 (XFEATURE_MASK_FP | XFEATURE_MASK_SSE \ >> | XFEATURE_MASK_YMM | XFEATURE_MASK_BNDREGS \ >> | XFEATURE_MASK_BNDCSR | XFEATURE_MASK_AVX512 \ >> - | XFEATURE_MASK_PKRU) >> + | XFEATURE_MASK_PKRU | XFEATURE_MASK_XTILE) >> >> u64 __read_mostly host_efer; >> EXPORT_SYMBOL_GPL(host_efer); >> @@ -946,6 +946,12 @@ static int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr) >> if ((xcr0 & XFEATURE_MASK_AVX512) != XFEATURE_MASK_AVX512) >> return 1; >> } >> + >> + if (xcr0 & XFEATURE_MASK_XTILE) { >> + if ((xcr0 & XFEATURE_MASK_XTILE) != XFEATURE_MASK_XTILE) >> + return 1; >> + } >> + >> vcpu->arch.xcr0 = xcr0; >> >> if ((xcr0 ^ old_xcr0) & XFEATURE_MASK_EXTEND) >> -- >> 2.18.4 >>
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