Re: [PATCH v2 0/7] xen/arm: Sanitize cpuinfo

[Julien Grall <julien@xxxxxxx>]

Hi Bertrand,

On 23/08/2021 11:32, Bertrand Marquis wrote:
> On arm architecture we might have heterogeneous platforms with different
> types of cores. As a guest can potentialy run on any of those cores we
> have to present them cpu features which are compatible with all cores
> and discard the features which are only available on some cores.
Sanitizing the CPU info is important for Xen so it can correctly size 
the P2M, flush the cache... However, I don't think this is going to be 
sufficient to be able to move a vCPU between different type of pCPU.
The main hurdle I can see so far is errata handling. Not all the errata 
can be fully handled in Xen so some of them are left to the guest to 
mitigate.
The errata are usually detected based on the MIDR while the OS is 
booting. IOW, a guest will not be able to know that it needs to handle 
an errata for pCPU B if it only runs on pCPU A.
I don't know yet how this can be solved, but errata are not that 
uncommon on Arm. So until this addressed, we will still need to make 
sure that vCPUs are not migrated between pCPUs with at least a different 
MIDR.
This prevention can be either done manually by pinning the vCPUs or 
implementing the proposal that Dario sent a few years ago (see [1]).
Cheers,

[1] 
https://lists.xenproject.org/archives/html/xen-devel/2016-12/msg00826.html
--
Julien Grall