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

[Julien Grall <julien.grall@xxxxxxx>]

On 31/08/16 16:06, Konrad Rzeszutek Wilk wrote:
> 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.
I only chat with Andrew about it and I have not looked at the code, so I 
can't tell how it is on x86. I was just thinking to add LIVEPATCH bit in 
cpufeature.h for now and be worry later when cpufeature will be exposed 
to the toolstack for ARM.
Cheers,

--
Julien Grall

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