linux-kernel - [PATCH v0 3/3] livepatch: update documentation for shadow variables

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Message-Id: <1519421630-12025-4-git-send-email-joe.lawrence@redhat.com>
Date:   Fri, 23 Feb 2018 16:33:50 -0500
From:   Joe Lawrence <joe.lawrence@...hat.com>
To:     live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>, Jessica Yu <jeyu@...nel.org>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Jason Baron <jbaron@...mai.com>,
        Evgenii Shatokhin <eshatokhin@...tuozzo.com>
Subject: [PATCH v0 3/3] livepatch: update documentation for shadow variables

Update livepatch shadow variable documentation with respect to new
atomic replace / cumulative patch functionality.

Signed-off-by: Joe Lawrence <joe.lawrence@...hat.com>
---
 Documentation/livepatch/shadow-vars.txt | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/Documentation/livepatch/shadow-vars.txt b/Documentation/livepatch/shadow-vars.txt
index 89c66634d600..9a2754cf551c 100644
--- a/Documentation/livepatch/shadow-vars.txt
+++ b/Documentation/livepatch/shadow-vars.txt
@@ -179,6 +179,30 @@ doesn't matter what data value the shadow variable holds, its existence
 suggests how to handle the parent object.
 
 
+Use in cumulative patches
+-------------------------
+
+Cumulative livepatches provide a "one-stop" module containing all active
+livepatch code.  A cumulative patch disables and replaces any previously
+loaded livepatch.  Shadow variable lifetimes should be carefully
+considered when loading cumulative livepatches:
+
+- If shadow variables lifetimes are specific to livepatch module
+  versions, it may make sense to free them when the corresponding
+  livepatch module is unloaded.
+
+- If shadow variable instances may be safely handled across cumulative
+  livepatch module versions, then it may make sense to free them from
+  unpatch callbacks.  When a cumulative patch replaces an existing
+  livepatch, only the cumulative patch's callbacks will be executed.
+  This means that new cumulative livepatches may be loaded while
+  deprecated / disabled livepatches may be unloaded without clearing
+  existing shadow variables.
+
+See Documentation/livepatch/callbacks.txt and cumulative.txt for more
+information on these subjects.
+
+
 3. References
 =============
 
-- 
1.8.3.1