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| author | Miroslav Benes <mbenes@suse.cz> | 2017-01-06 15:00:45 +0100 |
|---|---|---|
| committer | Jiri Kosina <jkosina@suse.cz> | 2017-01-11 02:33:39 +0100 |
| commit | 372e2db7210df7c45ead46429aeb1443ba148060 (patch) | |
| tree | 57c22c2df311ba846cdff8090329b8e1a230f151 /Documentation/livepatch | |
| parent | b766922e65356df38a57b09afab6c3d7bf7e024d (diff) | |
| download | lwn-372e2db7210df7c45ead46429aeb1443ba148060.tar.gz lwn-372e2db7210df7c45ead46429aeb1443ba148060.zip | |
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.txt | 19 |
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 |