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[34.125.23.197]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2aece5c1465sm38199815ad.21.2026.03.13.09.13.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 13 Mar 2026 09:13:13 -0700 (PDT) Date: Fri, 13 Mar 2026 16:13:08 +0000 From: Sami Tolvanen To: Will Deacon Cc: linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com, Ard Biesheuvel , Mark Rutland Subject: Re: [PATCH] arm64: scs: Remove redundant save/restore of SCS SP on entry to/from EL0 Message-ID: <20260313161308.GA213695@google.com> References: <20260313123220.29878-1-will@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260313123220.29878-1-will@kernel.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260313_091317_008011_36C07E94 X-CRM114-Status: GOOD ( 15.40 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Mar 13, 2026 at 12:32:19PM +0000, Will Deacon wrote: > When returning to userspace, the SCS is empty and so the SCS SP just > points to the base address of the SCS page. > > Rather than saving and restoring this address in the current task, we > can simply restore the SCS SP to point at the base of the stack on entry > to EL1 from EL0. > > Cc: Ard Biesheuvel > Cc: Mark Rutland > Cc: Sami Tolvanen > Signed-off-by: Will Deacon > --- > arch/arm64/include/asm/scs.h | 8 ++++++++ > arch/arm64/kernel/entry.S | 4 +--- > 2 files changed, 9 insertions(+), 3 deletions(-) > > I just spotted this by inspection when I was hacking on our exception > entry code. Reviewed-by: Sami Tolvanen Sami