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. - 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
