Re: [Xen-devel] [PATCH 09/14] livepatch: Add per-function applied/reverted state tracking marker

From: Julien Grall <julien.grall@arm.com>
To: Pawel Wieczorkiewicz <wipawel@amazon.de>,
	xen-devel@lists.xen.org, xen-devel@lists.xenproject.org
Cc: wipawel@amazon.com, "Stefano Stabellini" <sstabellini@kernel.org>,
	"Wei Liu" <wl@xen.org>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@oracle.com>,
	"George Dunlap" <George.Dunlap@eu.citrix.com>,
	"Andrew Cooper" <andrew.cooper3@citrix.com>,
	"Ian Jackson" <ian.jackson@eu.citrix.com>,
	mpohlack@amazon.com, "Tim Deegan" <tim@xen.org>,
	"Ross Lagerwall" <ross.lagerwall@citrix.com>,
	"Jan Beulich" <jbeulich@suse.com>,
	"Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [Xen-devel] [PATCH 09/14] livepatch: Add per-function applied/reverted state tracking marker
Date: Wed, 21 Aug 2019 22:34:42 +0100	[thread overview]
Message-ID: <680c5b24-b3fd-97b6-c048-49a2bdba4a3d@arm.com> (raw)
In-Reply-To: <20190821081931.90887-10-wipawel@amazon.de>

Hi Pawel,

On 8/21/19 9:19 AM, Pawel Wieczorkiewicz wrote:
> Livepatch only tracks an entire payload applied/reverted state. But,
> with an option to supply the apply_payload() and/or revert_payload()
> functions as optional hooks, it becomes possible to intermix the
> execution of the original apply_payload()/revert_payload() functions
> with their dynamically supplied counterparts.
> It is important then to track the current state of every function
> being patched and prevent situations of unintentional double-apply
> or unapplied revert.
> 
> To support that, it is necessary to extend public interface of the
> livepatch. The struct livepatch_func gets additional field holding
> the applied/reverted state marker.
> 
> To reflect the livepatch payload ABI change, bump the version flag
> LIVEPATCH_PAYLOAD_VERSION up to 2.
> 
> The above solution only applies to x86 architecture for now.

Is this going to break livepatch on Arm? If so, do you have any plan to 
fix it?

[...]

> diff --git a/xen/include/xen/livepatch.h b/xen/include/xen/livepatch.h
> index 2aec532ee2..a93126f631 100644
> --- a/xen/include/xen/livepatch.h
> +++ b/xen/include/xen/livepatch.h
> @@ -117,7 +117,7 @@ int arch_livepatch_quiesce(void);
>   void arch_livepatch_revive(void);
>   
>   void arch_livepatch_apply(struct livepatch_func *func);
> -void arch_livepatch_revert(const struct livepatch_func *func);
> +void arch_livepatch_revert(struct livepatch_func *func);

I doubt livepatch on Arm will compile after this change.

>   void arch_livepatch_post_action(void);
>   
>   void arch_livepatch_mask(void);

Cheers,

-- 
Julien Grall

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