Re: [PATCH 0/7] xen/arm: Emulate ID registers

[Bertrand Marquis <Bertrand.Marquis@arm.com>]

Hi Andrew,

> On 27 Nov 2020, at 20:07, Andrew Cooper <andrew.cooper3@citrix.com> wrote:
> 
> On 26/11/2020 15:51, Bertrand Marquis wrote:
>> The goal of this serie is to emulate coprocessor ID registers so that
>> Xen only publish to guest features that are supported by Xen and can
>> actually be used by guests.
>> One practical example where this is required are SVE support which is
>> forbidden by Xen as it is not supported, but if Linux is compiled with
>> it, it will crash on boot. An other one is AMU which is also forbidden
>> by Xen but one Linux compiled with it would crash if the platform
>> supports it.
>> 
>> To be able to emulate the coprocessor registers defining what features
>> are supported by the hardware, the TID3 bit of HCR must be disabled and
>> Xen must emulated the values of those registers when an exception is
>> catched when a guest is accessing it.
>> 
>> This serie is first creating a guest cpuinfo structure which will
>> contain the values that we want to publish to the guests and then
>> provides the proper emulationg for those registers when Xen is getting
>> an exception due to an access to any of those registers.
>> 
>> This is a first simple implementation to solve the problem and the way
>> to define the values that we provide to guests and which features are
>> disabled will be in a future patchset enhance so that we could decide
>> per guest what can be used or not and depending on this deduce the bits
>> to activate in HCR and the values that we must publish on ID registers.
>> 
>> Bertrand Marquis (7):
>>  xen/arm: Add ID registers and complete cpufinfo
>>  xen/arm: Add arm64 ID registers definitions
>>  xen/arm: create a cpuinfo structure for guest
>>  xen/arm: Add handler for ID registers on arm64
>>  xen/arm: Add handler for cp15 ID registers
>>  xen/arm: Add CP10 exception support to handle VMFR
>>  xen/arm: Activate TID3 in HCR_EL2
> 
> CI found an ARM randconfig failure against this series.
> 
> https://gitlab.com/xen-project/patchew/xen/-/pipelines/221798884
> 
> I have admit that I can't spot an obvious connection so it might be
> collateral damage from elsewhere, but does need looking at irrespective.

This absolutely right, there is a bug in my code and i will send a V2 to fix it.

Very nice finding, i am wondering why my tests did not point this out.

Regards
Bertrand

> 
> ~Andrew (in lieu of a real CI robot).