Re: [PATCH v1 5/8] kvm:x86 Enable MSR_IA32_XSS bit 11 and 12 for CET xsaves/xrstors.

[Jim Mattson]

On Wed, Jan 2, 2019 at 10:24 AM Sean Christopherson
<sean.j.christopherson@xxxxxxxxx> wrote:
>
> On Wed, Dec 26, 2018 at 04:15:29PM +0800, Yang Weijiang wrote:
> > For kvm Guest OS, right now, only bit 11(user mode CET) and bit 12
> > (supervisor CET) are supported in XSS MSR, if other bits are being set,
> > the write to XSS will be skipped.
> >
> > Signed-off-by: Zhang Yi Z <yi.z.zhang@xxxxxxxxxxxxxxx>
> > Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
> > ---
> >  arch/x86/kvm/vmx.c | 11 ++++++++---
> >  1 file changed, 8 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> > index fa2db6248404..5739ab393b90 100644
> > --- a/arch/x86/kvm/vmx.c
> > +++ b/arch/x86/kvm/vmx.c
> > @@ -47,6 +47,7 @@
> >  #include <asm/virtext.h>
> >  #include <asm/mce.h>
> >  #include <asm/fpu/internal.h>
> > +#include <asm/fpu/types.h>
> >  #include <asm/perf_event.h>
> >  #include <asm/debugreg.h>
> >  #include <asm/kexec.h>
> > @@ -4323,12 +4324,16 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> >       case MSR_IA32_XSS:
> >               if (!vmx_xsaves_supported())
> >                       return 1;
> > +
> >               /*
> > -              * The only supported bit as of Skylake is bit 8, but
> > -              * it is not supported on KVM.
> > +              * Right now, only support XSS_CET_U[bit 11] and
> > +              * XSS_CET_S[bit 12] in MSR_IA32_XSS.
> >                */
> > -             if (data != 0)
> > +
> > +             if (data & ~(XFEATURE_MASK_SHSTK_USER
> > +                          | XFEATURE_MASK_SHSTK_KERNEL))
>
> New lines are usually after the operator, e.g.:
>
>         if (data & ~(XFEATURE_MASK_SHSTK_USER |
>                      XFEATURE_MASK_SHSTK_KERNEL))
>
> And doesn't this flow need to check that the bits are actually supported?
Supported on the host and in the guest.