linux-kernel - Re: [PATCH v3 0/2] arm64: livepatch: Enable livepatch without sframe

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Message-ID: <Z_fhAyzPLNtPf5fG@pathway.suse.cz>
Date: Thu, 10 Apr 2025 17:17:23 +0200
From: Petr Mladek <pmladek@...e.com>
To: Song Liu <song@...nel.org>, mark.rutland@....com
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-toolchains@...r.kernel.org, live-patching@...r.kernel.org,
	indu.bhagat@...cle.com, puranjay@...nel.org, wnliu@...gle.com,
	irogers@...gle.com, joe.lawrence@...hat.com, jpoimboe@...nel.org,
	peterz@...radead.org, roman.gushchin@...ux.dev, rostedt@...dmis.org,
	will@...nel.org, kernel-team@...a.com
Subject: Re: [PATCH v3 0/2] arm64: livepatch: Enable livepatch without sframe

On Thu 2025-03-20 10:15:57, Song Liu wrote:
> There are recent efforts to enable livepatch for arm64, with sframe [1] or
> without sframe [2]. This set tries to enable livepatch without sframe. Some
> of the code, however, are from [1].
> 
> Although the sframe implementation is more promising in longer term, it
> suffers from the following issues:
> 
>   1. sframe is not yet supported in llvm;
>   2. There is still bug in binutil [3], so that we cannot yet use sframe
>      with gcc;
>   3. sframe unwinder hasn't been fully verified in the kernel.
> 
> On the other hand, arm64 processors have become more and more important in
> the data center world. Therefore, it is getting critical to support
> livepatching of arm64 kernels.
> 
> With recent change in arm64 unwinder [4], it is possible to reliably
> livepatch arm64 kernels without sframe. This is because we do not need
> arch_stack_walk_reliable() to get reliable stack trace in all scenarios.
> Instead, we only need arch_stack_walk_reliable() to detect when the
> stack trace is not reliable, then the livepatch logic can retry the patch
> transition at a later time.
> 
> Given the increasing need of livepatching, and relatively long time before
> sframe is fully ready (for both gcc and clang), we would like to enable
> livepatch without sframe.
> 
> Thanks!
> 
> [1] https://lore.kernel.org/live-patching/20250127213310.2496133-1-wnliu@google.com/
> [2] https://lore.kernel.org/live-patching/20250129232936.1795412-1-song@kernel.org/
> [3] https://sourceware.org/bugzilla/show_bug.cgi?id=32589
> [4] https://lore.kernel.org/linux-arm-kernel/20241017092538.1859841-1-mark.rutland@arm.com/
> 
> Changes v2 => v3:
> 1. Remove a redundant check for -ENOENT. (Josh Poimboeuf)
> 2. Add Tested-by and Acked-by on v1. (I forgot to add them in v2.)

The approach and both patches look reasonable:

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

Is anyone, Arm people, Mark, against pushing this into linux-next,
please?

Best Regards,
Petr