On 31/08/16 16:24, Andrew Cooper wrote:
On 31/08/16 16:09, Julien Grall wrote:
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.
Sorry - I have forgotten what exactly the purpose of this bit needs to
be, and therefore which bit of x86 I point you at.
The purpose of this bit is to be able to test the alternative with
livepatching on any platform.
All the current feature bits are for errata and none of them are common
enough to ensure a proper testing.
So I suggested to Konrad to introduce a feature bit LIVEPATCH that would
be enabled unconditionally or when debug is enabled. So if you load the
hello world payload, the alternative code will effectively be exercised.
Cheers,
--
Julien Grall
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
https://lists.xen.org/xen-devel
