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arm64: scs: Remove redundant save/restore of SCS SP on entry to/from EL0

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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>
Signed-off-by: Will Deacon <will@kernel.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Will Deacon 2026-03-13 12:32:19 +00:00 committed by Catalin Marinas
parent 6712fcde00
commit 3ce8f5860f
2 changed files with 9 additions and 3 deletions
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8
arch/arm64/include/asm/scs.h
View File

@ -10,6 +10,11 @@
#ifdef CONFIG_SHADOW_CALL_STACK
scs_sp .req x18
.macro scs_load_current_base
get_current_task scs_sp
ldr scs_sp, [scs_sp, #TSK_TI_SCS_BASE]
.endm
.macro scs_load_current
get_current_task scs_sp
ldr scs_sp, [scs_sp, #TSK_TI_SCS_SP]
@ -19,6 +24,9 @@
str scs_sp, [\tsk, #TSK_TI_SCS_SP]
.endm
#else
.macro scs_load_current_base
.endm
.macro scs_load_current
.endm

4
arch/arm64/kernel/entry.S
View File

@ -273,7 +273,7 @@ alternative_if ARM64_HAS_ADDRESS_AUTH
alternative_else_nop_endif
1:
scs_load_current
scs_load_current_base
.else
add x21, sp, #PT_REGS_SIZE
get_current_task tsk
@ -378,8 +378,6 @@ alternative_if ARM64_WORKAROUND_845719
alternative_else_nop_endif
#endif
3:
scs_save tsk
/* Ignore asynchronous tag check faults in the uaccess routines */
ldr x0, [tsk, THREAD_SCTLR_USER]
clear_mte_async_tcf x0