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Subject[PATCHv5 12/21] arm64: don't reload GPRs after apply_ssbd
Date
Now that all of the syscall logic works on the saved pt_regs, apply_ssbd
can safely corrupt x0-x3 in the entry paths, and we no longer need to
restore them. So let's remove the logic doing so.

With that logic gone, we can fold the branch target into the macro, so
that callers need not deal with this. GAS provides \@, which provides a
unique value per macro invocation, which we can use to create a unique
label.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
---
arch/arm64/kernel/entry.S | 20 +++++++-------------
1 file changed, 7 insertions(+), 13 deletions(-)

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index c41b84d06644..22b240da949b 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -130,20 +130,21 @@ alternative_else_nop_endif

// This macro corrupts x0-x3. It is the caller's duty
// to save/restore them if required.
- .macro apply_ssbd, state, targ, tmp1, tmp2
+ .macro apply_ssbd, state, tmp1, tmp2
#ifdef CONFIG_ARM64_SSBD
alternative_cb arm64_enable_wa2_handling
- b \targ
+ b .L__asm_ssbd_skip\@
alternative_cb_end
ldr_this_cpu \tmp2, arm64_ssbd_callback_required, \tmp1
- cbz \tmp2, \targ
+ cbz \tmp2, .L__asm_ssbd_skip\@
ldr \tmp2, [tsk, #TSK_TI_FLAGS]
- tbnz \tmp2, #TIF_SSBD, \targ
+ tbnz \tmp2, #TIF_SSBD, .L__asm_ssbd_skip\@
mov w0, #ARM_SMCCC_ARCH_WORKAROUND_2
mov w1, #\state
alternative_cb arm64_update_smccc_conduit
nop // Patched to SMC/HVC #0
alternative_cb_end
+.L__asm_ssbd_skip\@:
#endif
.endm

@@ -173,13 +174,7 @@ alternative_cb_end
ldr x19, [tsk, #TSK_TI_FLAGS] // since we can unmask debug
disable_step_tsk x19, x20 // exceptions when scheduling.

- apply_ssbd 1, 1f, x22, x23
-
-#ifdef CONFIG_ARM64_SSBD
- ldp x0, x1, [sp, #16 * 0]
- ldp x2, x3, [sp, #16 * 1]
-#endif
-1:
+ apply_ssbd 1, x22, x23

mov x29, xzr // fp pointed to user-space
.else
@@ -321,8 +316,7 @@ alternative_if ARM64_WORKAROUND_845719
alternative_else_nop_endif
#endif
3:
- apply_ssbd 0, 5f, x0, x1
-5:
+ apply_ssbd 0, x0, x1
.endif

msr elr_el1, x21 // set up the return data
--
2.11.0
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