On Thursday 27 May 2010 18:02:31 Avi Kivity wrote:
> On 05/27/2010 12:48 PM, Sheng Yang wrote:
> > This patch enable save/restore of xsave state.
> >
> > Signed-off-by: Sheng Yang<sheng@xxxxxxxxxxxxxxx>
> > ---
> >
> > arch/x86/include/asm/kvm.h | 29 ++++++++++++++++
> > arch/x86/kvm/x86.c | 79
> > ++++++++++++++++++++++++++++++++++++++++++++ include/linux/kvm.h
> > | 6 +++
>
> Documentation/kvm/api.txt +++++++++++++
Yes...
>
> > +/* for KVM_CAP_XSAVE */
> > +struct kvm_xsave {
> > + struct {
> > + __u16 cwd;
> > + __u16 swd;
> > + __u16 twd;
> > + __u16 fop;
> > + __u64 rip;
> > + __u64 rdp;
> > + __u32 mxcsr;
> > + __u32 mxcsr_mask;
> > + __u32 st_space[32];
> > + __u32 xmm_space[64];
> > + __u32 padding[12];
> > + __u32 sw_reserved[12];
> > + } i387;
> > + struct {
> > + __u64 xstate_bv;
> > + __u64 reserved1[2];
> > + __u64 reserved2[5];
> > + } xsave_hdr;
> > + struct {
> > + __u32 ymmh_space[64];
> > + } ymmh;
> > + __u64 xcr0;
> > + __u32 padding[256];
> > +};
>
> Need to reserve way more space here for future xsave growth. I think at
> least 4K. LRB wa 32x512bit = 1K (though it probably isn't a candidate
> for vmx). Would be good to get an opinion from your processor architects.
Would check it.
>
> I don't think we need to detail the contents of the structures since
> they're described by the SDM; so we can have just a large array that is
> 1:1 with the xsave as saved by the fpu.
Um, I've tried that, but failed mysteriously... Would check what's wrong.
>
> If we do that then xcr0 needs to be in a separate structure, say
> kvm_xcr, with a flags field and reserved space of its own for future xcr
> growth.
I meant to put it into sregs, but found it's already full... How about "extended
sregs"?
>
> > @@ -2363,6 +2366,59 @@ static int kvm_vcpu_ioctl_x86_set_debugregs(struct
> > kvm_vcpu *vcpu,
> >
> > return 0;
> >
> > }
> >
> > +static void kvm_vcpu_ioctl_x86_get_xsave(struct kvm_vcpu *vcpu,
> > + struct kvm_xsave *guest_xsave)
> > +{
> > + struct xsave_struct *xsave =&vcpu->arch.guest_fpu.state->xsave;
> > +
> > + if (!cpu_has_xsave)
> > + return;
>
> Hm, it would be nice to make it backward compatible and return the
> legacy fpu instead. I think the layouts are compatible?
Sound good. But seems we still need KVM_CAP_XSAVE to use this interface, and
other processors would still go FPU interface. Seems didn't improve much?
>
> > +
> > + guest_xsave->i387.cwd = xsave->i387.cwd;
> > + guest_xsave->i387.swd = xsave->i387.swd;
> > + guest_xsave->i387.twd = xsave->i387.twd;
> > + guest_xsave->i387.fop = xsave->i387.fop;
> > + guest_xsave->i387.rip = xsave->i387.rip;
> > + guest_xsave->i387.rdp = xsave->i387.rdp;
> > + memcpy(guest_xsave->i387.st_space, xsave->i387.st_space, 128);
> > + memcpy(guest_xsave->i387.xmm_space, xsave->i387.xmm_space,
> > + sizeof guest_xsave->i387.xmm_space);
> > +
> > + guest_xsave->xsave_hdr.xstate_bv = xsave->xsave_hdr.xstate_bv;
> > + memcpy(guest_xsave->ymmh.ymmh_space, xsave->ymmh.ymmh_space,
> > + sizeof xsave->ymmh.ymmh_space);
>
> And we can do a big memcpy here. But we need to limit it to what the
> host actually allocated.
Would try.
>
> > +
> > + guest_xsave->xcr0 = vcpu->arch.xcr0;
> > +}
> > +
> >
> > long kvm_arch_vcpu_ioctl(struct file *filp,
> >
> > unsigned int ioctl, unsigned long arg)
> >
> > {
> >
> > @@ -2564,6 +2620,29 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
> >
> > r = kvm_vcpu_ioctl_x86_set_debugregs(vcpu,&dbgregs);
> > break;
> >
> > }
> >
> > + case KVM_GET_XSAVE: {
> > + struct kvm_xsave xsave;
>
> Too big for stack (especially if we reserve room for growth).
Oops...
>
> > diff --git a/include/linux/kvm.h b/include/linux/kvm.h
> > index 23ea022..5006761 100644
> > --- a/include/linux/kvm.h
> > +++ b/include/linux/kvm.h
> > @@ -524,6 +524,9 @@ struct kvm_enable_cap {
> >
> > #define KVM_CAP_PPC_OSI 52
> > #define KVM_CAP_PPC_UNSET_IRQ 53
> > #define KVM_CAP_ENABLE_CAP 54
> >
> > +#ifdef __KVM_HAVE_XSAVE
> > +#define KVM_CAP_XSAVE 55
> > +#endif
>
> Might make sense to have a separate KVM_CAP_XCR, just for consistency.
Maybe EXTENDED_SREGS? But still every future field in the struct need a CAP...
--
regards
Yang, Sheng
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