On Fri, 2023-09-22 at 16:49 +0100, Paul Durrant wrote: > On 22/09/2023 16:44, David Woodhouse wrote: > > On Fri, 2023-09-22 at 15:00 +0000, Paul Durrant wrote: > > > From: Paul Durrant <pdurrant@xxxxxxxxxx> > > > > > > If the guest does not explicitly set the GPA of vcpu_info structure in > > > memory then, for guests with 32 vCPUs or fewer, the vcpu_info embedded > > > in the shared_info page may be used. As described in a previous commit, > > > the shared_info page is an overlay at a fixed HVA within the VMM, so in > > > this case it also more optimal to activate the vcpu_info cache with a > > > fixed HVA to avoid unnecessary invalidation if the guest memory layout > > > is modified. > > > > > > Signed-off-by: Paul Durrant <pdurrant@xxxxxxxxxx> > > > > But it should *only* be defined as an HVA in the case where it's the > > one in the shinfo. Otherwise, it's defined by its GPA. > > > > Which almost makes me want to see a sanity check that it precisely > > equals &shinfo->vcpu_info[vcpu->arch.xen.vcpu_id]. > > > > Which brings me back around the circle again to wonder why we don't > > just *default* to it.... you hate me, don't you? > > > > Your previous set of patches did that, and it did end requiring that > > the VMM restore both VCPU_INFO and VCPU_ID for each vCPU *before* > > restoring the SHARED_INFO_HVA on resume, but wasn't that OK? > > > > No. It was painful and overly complex, with too many corner cases that > were making my brain hurt. Given the pain of the last week, leaving the > default handling in the VMM is preferable. It means I don't need to > impose rules about attribute ordering and hence get caught by needing > one thread to wait for another inside the VMM. It's better and more > robust this way. Fair enough, I won't argue. That is fairly much the reason I ripped it out of João's original patch set in the first place :)
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