Re: [Xen-devel] [PATCH v2] Livepatch for ARM 64 and 32.

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Wed, Aug 31, 2016 at 03:49:55PM +0100, Julien Grall wrote:
> On 25/08/16 14:37, Konrad Rzeszutek Wilk wrote:
> > Hey!
> 
> Hi Konrad,
> 
> > Since v1 (and RFC): 
> > [https://lists.xen.org/archives/html/xen-devel/2016-08/msg01835.html]
> >  - Acted on most all comments.
> >  - Added ARM32 support.
> > 
> > The patches are based on: [PATCH v4] Livepatch fixes and features for v4.8.
> > (https://lists.xen.org/archives/html/xen-devel/2016-08/msg02705.html)
> > 
> > And the git tree is:
> >  git://xenbits.xen.org/people/konradwilk/xen.git livepatch.v4.8.v4
> > 
> > There are two outstanding questions that should be addressed at some point:
> >  -  #16 "livepatch: tests: Make them compile under ARM64"
> >     We chatted about adding a specific CPU bit (LIVEPATCH) so that 
> > alternative
> >     code always gets exercised. This being for both x86 and ARM. But this 
> > has
> >     a side effect that it gets exposed to the toolstack and can also be
> >     exposed to the guests. I think it is better if we do not do that
> >     so left it to be enabled based on the most common errata (or feature
> >     on x86).
> 
> There is no common errata on ARM. I spoke with Andrew which mentioned that
> on x86 they have architectural xen feature bits which are not exposed to the
> toolstack/guest.
> 
> Furthermore, I think it would be unwise to let the toolstack aware of some
> errata and possibly setting/clearing them. So adding a specific feature bit
> is fine by me.

So you are thinking of exposing this 'xen feature bits' that Andrew mention
to be on ARM as well.

Andrew, is this the 'Hypervisor' one?

> 
> >  -  #13 "livepatch: Initial ARM64 support."
> >     Need to look in erratum #843419 on some Cortex-A53 and figuring
> >     out how to avoid payloads having R_AARCH64_ADR_PREL_PG_HI21 relocations.
> 
> I will not considered this has a blocker for this series. Having
> livepatching on all the other boards for Xen 4.8 would still be awesome :).
> 
> Regards,
> 
> -- 
> Julien Grall

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