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Thu, 10 Apr 2025 08:17:24 -0700 (PDT) Date: Thu, 10 Apr 2025 17:17:23 +0200 From: Petr Mladek To: Song Liu , mark.rutland@arm.com Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-toolchains@vger.kernel.org, live-patching@vger.kernel.org, indu.bhagat@oracle.com, puranjay@kernel.org, wnliu@google.com, irogers@google.com, joe.lawrence@redhat.com, jpoimboe@kernel.org, peterz@infradead.org, roman.gushchin@linux.dev, rostedt@goodmis.org, will@kernel.org, kernel-team@meta.com Subject: Re: [PATCH v3 0/2] arm64: livepatch: Enable livepatch without sframe Message-ID: References: <20250320171559.3423224-1-song@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250320171559.3423224-1-song@kernel.org> 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 Is anyone, Arm people, Mark, against pushing this into linux-next, please? Best Regards, Petr