KVM, pkeys: do not use PKRU value in vcpu->arch.guest_fpu.state

KVM, pkeys: do not use PKRU value in vcpu->arch.guest_fpu.state

The host pkru is restored right after vcpu exit (commit 1be0e61), so
KVM_GET_XSAVE will return the host PKRU value instead.  Fix this by
using the guest PKRU explicitly in fill_xsave and load_xsave.  This
part is based on a patch by Junkang Fu.

The host PKRU data may also not match the value in vcpu->arch.guest_fpu.state,
because it could have been changed by userspace since the last time
it was saved, so skip loading it in kvm_load_guest_fpu.

Reported-by: Junkang Fu <[email protected]>
Cc: Yang Zhang <[email protected]>
Fixes: 1be0e61c1f255faaeab04a390e00c8b9b9042870
Cc: [email protected]
Signed-off-by: Paolo Bonzini <[email protected]>