linux-kernel - Re: [PATCH v5 3/3] selftests: livepatch: Test livepatching a heavily called syscall

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Date: Thu, 11 Jan 2024 14:36:56 +0100
From: Petr Mladek <pmladek@...e.com>
To: Marcos Paulo de Souza <mpdesouza@...e.com>
Cc: Shuah Khan <shuah@...nel.org>, Jonathan Corbet <corbet@....net>,
	Heiko Carstens <hca@...ux.ibm.com>,
	Vasily Gorbik <gor@...ux.ibm.com>,
	Alexander Gordeev <agordeev@...ux.ibm.com>,
	Christian Borntraeger <borntraeger@...ux.ibm.com>,
	Sven Schnelle <svens@...ux.ibm.com>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Jiri Kosina <jikos@...nel.org>, Miroslav Benes <mbenes@...e.cz>,
	Joe Lawrence <joe.lawrence@...hat.com>,
	linux-kselftest@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
	live-patching@...r.kernel.org
Subject: Re: [PATCH v5 3/3] selftests: livepatch: Test livepatching a heavily
 called syscall

On Tue 2024-01-09 21:24:56, Marcos Paulo de Souza wrote:
> The test proves that a syscall can be livepatched. It is interesting
> because syscalls are called a tricky way. Also the process gets
> livepatched either when sleeping in the userspace or when entering
> or leaving the kernel space.
> 
> The livepatch is a bit tricky:
>   1. The syscall function name is architecture specific. Also
>      ARCH_HAS_SYSCALL_WRAPPER must be taken in account.
> 
>   2. The syscall must stay working the same way for other processes
>      on the system. It is solved by decrementing a counter only
>      for PIDs of the test processes. It means that the test processes
>      has to call the livepatched syscall at least once.
> 
> The test creates one userspace process per online cpu. The processes
> are calling getpid in a busy loop. The intention is to create random
> locations when the livepatch gets enabled. Nothing is guarantted.
> The magic is in the randomness.
> 
> Reviewed-by: Joe Lawrence <joe.lawrence@...hat.com>
> Signed-off-by: Marcos Paulo de Souza <mpdesouza@...e.com>

Reviewed-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr