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From: Sami Tolvanen <samitolvanen@google.com>
To: Will Deacon <will@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com,
	Ard Biesheuvel <ardb@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>
Subject: Re: [PATCH] arm64: scs: Remove redundant save/restore of SCS SP on entry to/from EL0
Date: Fri, 13 Mar 2026 16:13:08 +0000	[thread overview]
Message-ID: <20260313161308.GA213695@google.com> (raw)
In-Reply-To: <20260313123220.29878-1-will@kernel.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 <ardb@kernel.org>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Sami Tolvanen <samitolvanen@google.com>
> Signed-off-by: Will Deacon <will@kernel.org>
> ---
>  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 <samitolvanen@google.com>

Sami


  parent reply	other threads:[~2026-03-13 16:13 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-03-13 12:32 [PATCH] arm64: scs: Remove redundant save/restore of SCS SP on entry to/from EL0 Will Deacon
2026-03-13 13:26 ` Ard Biesheuvel
2026-03-13 14:18 ` Mark Rutland
2026-03-13 16:13 ` Sami Tolvanen [this message]
2026-03-13 19:42 ` Catalin Marinas

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