Re: [Xen-devel] Ping: [PATCH] x86: improve vCPU selection in pagetable_dying()

[Tim Deegan <tim@xxxxxxx>]

At 17:56 +0100 on 03 Oct (1538589366), George Dunlap wrote:
> On 09/26/2018 08:04 AM, Jan Beulich wrote:
> > Looking at things again (in particular
> > the comment ahead of pagetable_dying()) I now actually wonder why
> > HVMOP_pagetable_dying is permitted to be called by other than a domain
> > for itself. There's no use of it in the tool stack. Disallowing the unused
> > case would mean the fast-path logic in sh_pagetable_dying() could
> > become the only valid/implemented case. Tim?
> 
> Not so -- a guest could still call pagetable_dying() on the top level PT
> of a process not currently running.
> 
> I would be totally in favor of limiting this call to the guest itself,
> however -- that would simplify the logic even more.

Yes, I think that this can be restricted to the caller's domain, and
so always use current as the vcpu.  I don't recall a use case for
setting this from outside the VM.

I can't find reason for the vcpu[0] in the history, but it does look
wrong.  I suspect this patch might have been in a XenServer patch
queue for a while, and perhaps the plumbing was fixed up incorrectly
when it was upstreamed.

Cheers,

Tim.

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