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

[Mark Rutland <mark.rutland@arm.com>]

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