lkml.org 
[lkml]   [2021]   [Feb]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v1] kvm: x86: Revise guest_fpu xcomp_bv field
On Mon, Feb 08, 2021, Dave Hansen wrote:
> On 2/8/21 8:16 AM, Jing Liu wrote:
> > -#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;

This is wrong, xfeatures_mask_all also tracks supervisor states.

> Are 'host_xcr0' and 'xfeatures_mask_all' really interchangeable? If so,
> shouldn't we just remove 'host_xcr0' everywhere?

I think so? But use xfeatures_mask_user().

In theory, host_xss can also be replaced with the _supervisor() and _dynamic()
variants. That code needs a good hard look at the _dynamic() features, which is
currently just architectural LBRs. E.g. I wouldn't be surprised if KVM currently
fails to save/restore arch LBRs due to the bit not being set in host_xss.

\
 
 \ /
  Last update: 2021-02-08 20:03    [W:2.149 / U:1.680 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site