Re: [PATCH] xen/arm: Add Cortex-A73 erratum 858921 workaround

[Julien Grall <julien@xxxxxxx>]

Hi,

On 09/11/2020 08:21, Penny Zheng wrote:
> CNTVCT_EL0 or CNTPCT_EL0 counter read in Cortex-A73 (all versions)
> might return a wrong value when the counter crosses a 32bit boundary.
>
> Until now, there is no case for Xen itself to access CNTVCT_EL0,
> and it also should be the Guest OS's responsibility to deal with
> this part.
>
> But for CNTPCT, there exists several cases in Xen involving reading
> CNTPCT, so a possible workaround is that performing the read twice,
> and to return one or the other depending on whether a transition has
> taken place.
>
> Signed-off-by: Penny Zheng <penny.zheng@xxxxxxx>
Acked-by: Julien Grall <jgrall@xxxxxxxxxx>

On a related topic, do we need a fix similar to Linux commit 
75a19a0202db "arm64: arch_timer: Ensure counter register reads occur 
with seqlock held"?
Cheers,

--
Julien Grall