On 22/11/2023 10:39, David Woodhouse wrote:
On Tue, 2023-11-21 at 22:53 +0000, David Woodhouse wrote:
On Tue, 2023-11-21 at 18:02 +0000, Paul Durrant wrote:
From: Paul Durrant <pdurrant@xxxxxxxxxx>
If the guest sets an explicit vcpu_info GPA then, for any of the first 32
vCPUs, the content of the default vcpu_info in the shared_info page must be
copied into the new location. Because this copy may race with event
delivery (which updates the 'evtchn_pending_sel' field in vcpu_info) there
needs to be a way to defer that until the copy is complete.
Happily there is already a shadow of 'evtchn_pending_sel' in kvm_vcpu_xen
that is used in atomic context if the vcpu_info PFN cache has been
invalidated so that the update of vcpu_info can be deferred until the
cache can be refreshed (on vCPU thread's the way back into guest context).
Also use this shadow if the vcpu_info cache has been *deactivated*, so that
the VMM can safely copy the vcpu_info content and then re-activate the
cache with the new GPA. To do this, stop considering an inactive vcpu_info
cache as a hard error in kvm_xen_set_evtchn_fast().
Signed-off-by: Paul Durrant <pdurrant@xxxxxxxxxx>
Reviewed-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
Wait, didn't we realise that this leaves the bits set in the shadow
evtchn_pending_sel that get lost on migration?
Indeed we did not, but that's not something that *this* patch, or even
this series, is dealing with. We also know that setting the 'width' of
shared_info has some issues, but again, can we keep that for other
patches? The series is at v9 and has already suffered a fair amount of
scope-creep.
Paul
