x86/msr: Virtualise MSR_FLUSH_CMD for guests
Guests (outside of the nested virt case, which isn't supported yet) don't need
L1D_FLUSH for their L1TF mitigations, but offering/emulating MSR_FLUSH_CMD is
easy and doesn't pose an issue for Xen.
The MSR is offered to HVM guests only. PV guests attempting to use it would
trap for emulation, and the L1D cache would fill long before the return to
guest context. As such, PV guests can't make any use of the L1D_FLUSH
functionality.
This is part of XSA-273 / CVE-2018-3646.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
projects / xen.git / commit