Re: [Xen-devel] [PATCH v2 05/12] livepatch: Add support for apply|revert action replacement hooks

From: "Wieczorkiewicz, Pawel" <wipawel@amazon.de>
To: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Tim Deegan <tim@xen.org>,
	Stefano Stabellini <sstabellini@kernel.org>, Wei Liu <wl@xen.org>,
	Ross Lagerwall <ross.lagerwall@citrix.com>,
	George Dunlap <George.Dunlap@eu.citrix.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Ian Jackson <ian.jackson@eu.citrix.com>,
	xen-devel <xen-devel@lists.xen.org>,
	"Pohlack, Martin" <mpohlack@amazon.de>,
	"Wieczorkiewicz, Pawel" <wipawel@amazon.de>,
	Julien Grall <julien.grall@arm.com>,
	Jan Beulich <jbeulich@suse.com>,
	xen-devel <xen-devel@lists.xenproject.org>
Subject: Re: [Xen-devel] [PATCH v2 05/12] livepatch: Add support for apply|revert action replacement hooks
Date: Wed, 28 Aug 2019 07:37:22 +0000	[thread overview]
Message-ID: <F3A43E49-6F04-49A8-A5AD-5BABC14A02F2@amazon.com> (raw)
In-Reply-To: <AC4BE922-88D7-47B9-9CEC-D9413B22AB61@oracle.com>

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On 27. Aug 2019, at 18:58, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com<mailto:konrad.wilk@oracle.com>> wrote:

On August 27, 2019 4:46:17 AM EDT, Pawel Wieczorkiewicz <wipawel@amazon.de<mailto:wipawel@amazon.de>> wrote:
By default, in the quiescing zone, a hotpatch payload is applied with
apply_payload() and reverted with revert_payload() functions. Both of
the functions receive the payload struct pointer as a parameter. The
functions are also a place where standard 'load' and 'unload' module
hooks are executed.

To increase hotpatching system's agility and provide more flexiable
long-term hotpatch solution, allow to overwrite the default apply
and revert action functions with hook-like supplied alternatives.
The alternative functions are optional and the default functions are
used by default.

Is there sense in having the old ones anymore? We could just remove them altogether and just use the new ones instead from the start?

Yes, I believe there is. The old ones represent well-tested, proven way of
payload application (or revert) which preserves conservative behavior of the system
via enforcing certain assumptions.
The old ones cover 99% of the production use cases, so I would insist on keeping
them in (at least for now).

Later, we could modify livepatch-build-tools to always generate the original
apply|revert functions (in a default case) as part of payloads (hooks).
But, I would not do it just now.

Best Regards,
Pawel Wieczorkiewicz

Amazon Development Center Germany GmbH
Krausenstr. 38
10117 Berlin
Geschaeftsfuehrung: Christian Schlaeger, Ralf Herbrich
Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B
Sitz: Berlin
Ust-ID: DE 289 237 879

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