Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Tue, 12 Feb 2019 10:46:08 +0100
From:   Petr Mladek <pmladek@suse.com>
To:     Josh Poimboeuf <jpoimboe@redhat.com>
Cc:     Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>,
        live-patching@vger.kernel.org, linux-kernel@vger.kernel.org,
        Miroslav Benes <mbenes@suse.cz>, Jiri Kosina <jikos@kernel.org>
Subject: Re: [PATCH] livepatch: Enforce reliable stack trace as config
 dependency
Message-ID: <20190212094608.bzwc26j67daqnx6x@pathway.suse.cz>
References: <20190209091728.23046-1-kamalesh@linux.vnet.ibm.com>
 <20190211140813.z7kap634gz3gp6a4@treble>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20190211140813.z7kap634gz3gp6a4@treble>
User-Agent: NeoMutt/20170421 (1.8.2)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Mon 2019-02-11 08:08:13, Josh Poimboeuf wrote:
> Anyway, I'm not sure about this approach.  This patch makes the s390
> livepatch code no longer compilable, turning it into completely dead
> code.  So if something changes in the s390 code which causes it to stop
> compiling, nobody will notice.

Good point. Well, it is only small win when a code is buildable
but it could not get really used. Also the amount of arch-specific
code is really minimal.

> I think I'd rather go in the opposite direction: allow the patches to be
> loaded.  Then they can be forced, if needed.  That enables both compile
> and runtime testing.  That way we don't make any backward progress,
> until such arches get reliable stacktraces.

Do you mean to convert the error into warning?

For example, the change below. Note that I did not mention
the possibility to force the transition by intention. It is risky
and people should not get used to it.

Heh, I think that this was the main reason why it was the error.
We did not want to get people used to forcing livepatches.


diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index d1af69e9f0e3..8d9bce251516 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -1035,11 +1035,10 @@ int klp_enable_patch(struct klp_patch *patch)
 		return -ENODEV;
 
 	if (!klp_have_reliable_stack()) {
-		pr_err("This architecture doesn't have support for the livepatch consistency model.\n");
-		return -EOPNOTSUPP;
+		pr_warn("This architecture doesn't have support for the livepatch consistency model.\n");
+		pr_warn("Only one livepatch can be installed.\n");
 	}
 
-
 	mutex_lock(&klp_mutex);
 
 	ret = klp_init_patch_early(patch);


Best Regards,
Petr