arm64: don't reload GPRs after apply_ssbd

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>
Signed-off-by: Will Deacon <will.deacon@arm.com>

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index c41b84d..22b240d 100644 (file)
--- 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