Re: [PATCH v4 12/21] arm64: entry: sdei: Restore all clobberable GPRs

[Vladimir Murzin <vladimir.murzin@arm.com>]

On 9/8/26 16:17, Mark Rutland wrote:
> Currently __sdei_asm_handler() avoids restoring x20 to x27, as these are
> not be clobbered by existing code. This is correct today, but it makes
> it awkward to rework __sdei_asm_handler(). Given the rarity of SDEI
> events, restoring x20 to x27 should not have a measurable impact.
> 
> Restore x20 to x27 when returning from an SDEI event handler. This will
> free up those GPRs for usage in __sdei_asm_handler() prior to return.
> 
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
> Cc: Ada Couprie Diaz <ada.coupriediaz@arm.com>
> Cc: Ard Biesheuvel <ardb@kernel.org>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: James Morse <james.morse@arm.com>
> Cc: Jinjie Ruan <ruanjinjie@huawei.com>
> Cc: Marc Zyngier <maz@kernel.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Vladimir Murzin <vladimir.murzin@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Yang Shi <yang@os.amperecomputing.com>
> ---
>  arch/arm64/kernel/entry.S | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index f63049ac32dc6..a6ec5c5a2d29c 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -1044,10 +1044,14 @@ SYM_CODE_START(__sdei_asm_handler)
>  	bl	__sdei_handler
>  
>  	msr	sp_el0, x28
> -	/* restore regs >x17 that we clobbered */
> +	/* restore regs >x17 that firmware won't restore */
>  	mov	x4, x19         // keep x4 for __sdei_asm_exit_trampoline
> -	ldp	x28, x29, [x4, #SDEI_EVENT_INTREGS + 16 * 14]
>  	ldp	x18, x19, [x4, #SDEI_EVENT_INTREGS + 16 * 9]
> +	ldp	x20, x21, [x4, #SDEI_EVENT_INTREGS + 16 * 10]
> +	ldp	x22, x23, [x4, #SDEI_EVENT_INTREGS + 16 * 11]
> +	ldp	x24, x25, [x4, #SDEI_EVENT_INTREGS + 16 * 12]
> +	ldp	x26, x27, [x4, #SDEI_EVENT_INTREGS + 16 * 13]
> +	ldp	x28, x29, [x4, #SDEI_EVENT_INTREGS + 16 * 14]
>  	ldp	lr, x1, [x4, #SDEI_EVENT_INTREGS + S_LR]
>  	mov	sp, x1
>  
> -- 2.30.2
> 

FWIW,

Reviewed-by: Vladimir Murzin <vladimir.murzin@arm.com>