On 12/14/21 07:06, Wang, Wei W wrote:
On Monday, December 13, 2021 5:24 PM, Paolo Bonzini wrote:
There is no need for struct kvm_xsave2, because there is no need for a "size"
argument.
- KVM_GET_XSAVE2 *is* needed, and it can expect a buffer as big as the return
value of KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2)
Why would KVM_GET_XSAVE2 still be needed in this case?
I'm thinking it would also be possible to reuse KVM_GET_XSAVE:
- If userspace calls to KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2),
then KVM knows that the userspace is a new version and it works with larger xsave buffer using the "size" that it returns via KVM_CAP_XSAVE2.
So we can add a flag "kvm->xsave2_enabled", which gets set upon userspace checks KVM_CAP_XSAVE2.
You can use KVM_ENABLE_CAP(KVM_CAP_XSAVE2) for that, yes. In that case
you don't need KVM_GET_XSAVE2.
Paolo
- On KVM_GET_XSAVE, if "kvm->xsave2_enabled" is set,
then KVM allocates buffer to load xstates and copies the loaded xstates data to the userspace buffer
using the "size" that was returned to userspace on KVM_CAP_XSAVE2.
If "kvm->xsave2_enabled" isn't set, using the legacy "4KB" size.
Thanks,
Wei
