Re: [PATCH v2] xen/arm: Convert runstate address during hypcall

[Julien Grall <julien@xxxxxxx>]

Hi Jan,

On 31/07/2020 07:39, Jan Beulich wrote:
> We're fixing other issues without breaking the ABI. Where's the
> problem of backporting the kernel side change (which I anticipate
> to not be overly involved)?
This means you can't take advantage of the runstage on existing Linux 
without any modification.
> If the plan remains to be to make an ABI breaking change,
For a theoritical PoV, this is a ABI breakage. However, I fail to see 
how the restrictions added would affect OSes at least on Arm.
In particular, you can't change the VA -> PA on Arm without going 
through an invalid mapping. So I wouldn't expect this to happen for the 
runstate.
The only part that *may* be an issue is if the guest is registering the 
runstate with an initially invalid VA. Although, I have yet to see that 
in practice. Maybe you know?
>  then I
> think this will need an explicit vote.
I was under the impression that the two Arm maintainers (Stefano and I) 
already agreed with the approach here. Therefore, given the ABI breakage 
is only affecting Arm, why would we need a vote?
Cheers,

--
Julien Grall