On Monday, December 20, 2021 5:04 PM, Paolo Bonzini wrote:
> On 12/17/21 16:29, Jing Liu wrote:
> > +/* for KVM_CAP_XSAVE and KVM_CAP_XSAVE2 */
> > struct kvm_xsave {
> > + /*
> > + * KVM_GET_XSAVE only uses the first 4096 bytes.
> > + *
> > + * KVM_GET_XSAVE2 must have the size match what is returned by
> > + * KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2).
> > + *
> > + * KVM_SET_XSAVE uses the extra field if guest_fpu::fpstate::size
> > + * exceeds 4096 bytes.
>
> KVM_GET_XSAVE2 and KVM_SET_XSAVE respectively write and read as many
> bytes as are returned by KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2), when
> invoked on the vm file descriptor. Currently,
> KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2) will only return a value that is
> greater than 4096 bytes if any dynamic features have been enabled with
> ``arch_prctl()``; this however may change in the future.
Would this make people think that KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2) doesn’t
return the value (i.e. return 0) if it is smaller than 4096?
(i.e. KVM_GET_XSAVE2 doesn't work with size < 4096, which isn’t true)
I plan to just reword a bit:
Currently, KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2) will only return a size value,
and the value is greater than 4096 bytes if any dynamic features have been enabled with
``arch_prctl()``. More types of values could be returned in the future.
Thanks,
Wei
