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Mon, 29 Jul 2024 11:03:08 -0400 X-MC-Unique: wr2rRBWJNkK-it_mCdlYxQ-1 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id B86B91944D30; Mon, 29 Jul 2024 15:03:04 +0000 (UTC) Received: from sullivan-work.redhat.com (unknown [10.22.9.117]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 93C0F300019D; Mon, 29 Jul 2024 15:02:50 +0000 (UTC) From: Ryan Sullivan To: live-patching@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH] powerpc/ftrace: restore r2 to caller's stack on livepatch sibling call Date: Mon, 29 Jul 2024 11:02:36 -0400 Message-ID: <20240729150246.8939-1-rysulliv@redhat.com> In-Reply-To: <878qxkp9jl.fsf@mail.lhotse> References: <878qxkp9jl.fsf@mail.lhotse> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 X-Mailman-Approved-At: Tue, 30 Jul 2024 08:47:06 +1000 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: pmladek@suse.com, joe.lawrence@redhat.com, jikos@kernel.org, christophe.leroy@csgroup.eu, rysulliv@redhat.com, npiggin@gmail.com, naveen.n.rao@linux.ibm.com, mbenes@suse.cz, jpoimboe@kernel.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Hello Michael, In the case of no sibling call within the livepatch then the store is only "restoring" the r2 value that was already there as it is stored and retrieved from the livepatch stack. The only time that the r2 value is corrupted is in the case of a sibling call and thus this additional store is just restoring the caller's context as a safety precaution. Also should this explanation be put into the patch itself or will these messages suffice as a reference? Cheers, Ryan