Re: [Xen-devel] [TESTDAY] Test report

[Tamas K Lengyel <tamas.k.lengyel@xxxxxxxxx>]

On Fri, Nov 15, 2019 at 4:56 AM Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
>
> On 14/11/2019 22:36, Tamas K Lengyel wrote:
> > On Thu, Nov 14, 2019 at 11:39 AM Andrew Cooper
> > <andrew.cooper3@xxxxxxxxxx> wrote:
> >> On 14/11/2019 18:34, Tamas K Lengyel wrote:
> >>> * Comments: All works, altp2m+introspection requires the ept=pml=0
> >>> boot flag specified to workaround a deadlock in Xen
> >> Is this separate from the general problem with EPT A/D and
> >> write-protecting pagetables?
> >>
> > It sounds like it is, it happens without write-protecting in-guest
> > pagetables. I didn't have time to investigate where the deadlock
> > happens and since the workaround is fine for the usecase it wasn't a
> > priority to figure out.
>
> Thinking about it, PML will do the wrong thing (deadlocks aside) as soon
> as any altp2m gfn translations are used.
>
> I'd be tempted to work around the deadlock by disabling pml the moment
> altp2m is touched.  That would give a sightly less bad user experience,
> and should be easy to sort for 4.13.
>
> Thoughts, (inc. Juergen as RM) ?

That sounds like a good idea to me, that way you can keep pml for
guests where it doesn't cause an issue instead of disabling it system
wide.

Tamas

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