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authorMiroslav Benes <mbenes@suse.cz>2017-01-06 15:00:45 +0100
committerJiri Kosina <jkosina@suse.cz>2017-01-11 02:33:39 +0100
commit372e2db7210df7c45ead46429aeb1443ba148060 (patch)
tree57c22c2df311ba846cdff8090329b8e1a230f151 /Documentation/livepatch
parentb766922e65356df38a57b09afab6c3d7bf7e024d (diff)
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livepatch: doc: remove the limitation for schedule() patching
The Limitations section of the documentation describes the impossibility to livepatch anything that is inlined to __schedule() function. This had been true till 4.9 kernel came. Thanks to commit 0100301bfdf5 ("sched/x86: Rewrite the switch_to() code") from Brian Gerst there is __switch_to_asm function now (implemented in assembly) called properly from context_switch(). RIP is thus saved on the stack and a task would return to proper version of __schedule() et al. functions. Of course __switch_to_asm() is not patchable for the reason described in the section. But there is no __fentry__ call and I cannot imagine a reason to do it anyway. Therefore, remove the paragraphs from the section. Signed-off-by: Miroslav Benes <mbenes@suse.cz> Reviewed-by: Petr Mladek <pmladek@suse.com> Acked-by: Josh Poimboeuf <jpoimboe@redhat.com> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Diffstat (limited to 'Documentation/livepatch')
-rw-r--r--Documentation/livepatch/livepatch.txt19
1 files changed, 0 insertions, 19 deletions
diff --git a/Documentation/livepatch/livepatch.txt b/Documentation/livepatch/livepatch.txt
index f5967316deb9..7f04e13ec53d 100644
--- a/Documentation/livepatch/livepatch.txt
+++ b/Documentation/livepatch/livepatch.txt
@@ -329,25 +329,6 @@ The current Livepatch implementation has several limitations:
by "notrace".
- + Anything inlined into __schedule() can not be patched.
-
- The switch_to macro is inlined into __schedule(). It switches the
- context between two processes in the middle of the macro. It does
- not save RIP in x86_64 version (contrary to 32-bit version). Instead,
- the currently used __schedule()/switch_to() handles both processes.
-
- Now, let's have two different tasks. One calls the original
- __schedule(), its registers are stored in a defined order and it
- goes to sleep in the switch_to macro and some other task is restored
- using the original __schedule(). Then there is the second task which
- calls patched__schedule(), it goes to sleep there and the first task
- is picked by the patched__schedule(). Its RSP is restored and now
- the registers should be restored as well. But the order is different
- in the new patched__schedule(), so...
-
- There is work in progress to remove this limitation.
-
-
+ Livepatch modules can not be removed.
The current implementation just redirects the functions at the very