Re: [Xen-devel] 4.11.0 RC1 panic

[Manuel Bouyer <bouyer@xxxxxxxxxxxxxxx>]

On Mon, Jun 11, 2018 at 03:58:01AM -0600, Jan Beulich wrote:
> >>> On 10.06.18 at 18:32, <bouyer@xxxxxxxxxxxxxxx> wrote:
> > On Sun, Jun 10, 2018 at 09:38:17AM -0600, Jan Beulich wrote:
> >> What about L2 tables to be used in slot 3 of an L3 table? Aiui Xen won't 
> >> allow
> >> them to be pinned, hence I'd expect there to be some special casing in your
> >> code. Considering no similar issues have been observed with 64-bit guests,
> >> this one special case looks to me to be the prime suspect for something 
> >> going
> >> wrong (in Xen).
> > 
> > AFAIK this L2 is allocated at boot, and should never be freed. It's
> > shared by all CPUs.
> 
> I guess that's what goes into L3 slot 3 and ...

Yes

> 
> > There is one special L2 case: it's pinned as L2 but used as L1 in the 
> > "kernel"
> > L2 (the one in slot 3 of the L3 tables). This is for recursive mappings
> > of the kernel map. This one will be allocated/freed (and so pinned/unpinned)
> > for each context.
> 
> ... here you mean L3 slot 2 (all assuming 0-based slot numbering)?
> Otherwise I'm afraid I'm confused now, as the sharing by all CPUs of
> the former seems to contradict the per-context nature of the latter.

yes, sorry, it's referecened in the last entry of the "L3 slot 2" L2 page.

-- 
Manuel Bouyer <bouyer@xxxxxxxxxxxxxxx>
     NetBSD: 26 ans d'experience feront toujours la difference
--

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