Re: [Xen-devel] [PATCH for-4.13] xen/arm: livepatch: Prevent CPUs to fetch stale instructions after livepatching

[Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>]

Hi Julien,

Julien Grall writes:

> During livepatch, a single CPU will take care of applying the patch and
> all the others will wait for the action to complete. They will then once
> execute arch_livepatch_post_action() to flush the pipeline.
>
> Per B2.2.5 "Concurrent modification and execution of instructions" in
> DDI 0487E.a, flushing the instruction cache is not enough to ensure new
> instructions are seen. All the PEs should also do an isb() to
> synchronize the fetched instruction stream.
>
> Signed-off-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Volodymyr Babchuk <volodymyr_babchuk@epam.com>

> ---
>  xen/arch/arm/livepatch.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/xen/arch/arm/livepatch.c b/xen/arch/arm/livepatch.c
> index 279d52cc6c..00c5e2bc45 100644
> --- a/xen/arch/arm/livepatch.c
> +++ b/xen/arch/arm/livepatch.c
> @@ -88,7 +88,8 @@ void arch_livepatch_revert(const struct livepatch_func *func)
>  
>  void arch_livepatch_post_action(void)
>  {
> -    /* arch_livepatch_revive has nuked the instruction cache. */
> +    /* Discard any stale instructions that may have been fetched. */
> +    isb();
>  }
>  
>  void arch_livepatch_mask(void)


-- 
Volodymyr Babchuk at EPAM
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