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Re: [Xen-devel] [PATCH for-4.13] xen/arm: livepatch: Prevent CPUs to fetch stale instructions after livepatching
- To: Julien Grall <julien.grall@xxxxxxx>
- From: Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
- Date: Wed, 18 Sep 2019 16:21:21 +0000
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
- Delivery-date: Wed, 18 Sep 2019 16:21:31 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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- Thread-topic: [PATCH for-4.13] xen/arm: livepatch: Prevent CPUs to fetch stale instructions after livepatching
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@xxxxxxx>
Reviewed-by: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>
> ---
> 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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