arm64: entry.S: Remove disable_dbg

enable_step_tsk is the only user of disable_dbg, which doesn't respect
our 'dai' order for exception masking. enable_step_tsk may enable
single-step, so previously needed to mask debug exceptions to prevent us
from single-stepping kernel_exit. enable_step_tsk is called at the end
of the ret_to_user loop, which has already masked all exceptions so this
is no longer needed.

Remove disable_dbg, add a comment that enable_step_tsk's caller should
have masked debug.

Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Julien Thierry <julien.thierry@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index a4aa22241dd18ebcb439ef53a9ac231ba1a1c53b..8bc63fc98752992a9571b14dbe1116241ebc3726 100644 (file)
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -69,13 +69,6 @@
        msr     daif, \flags
        .endm
 
-/*
- * Enable and disable debug exceptions.
- */
-       .macro  disable_dbg
-       msr     daifset, #8
-       .endm
-
        .macro  enable_dbg
        msr     daifclr, #8
        .endm
@@ -89,9 +82,9 @@
 9990:
        .endm
 
+       /* call with daif masked */
        .macro  enable_step_tsk, flgs, tmp
        tbz     \flgs, #TIF_SINGLESTEP, 9990f
-       disable_dbg
        mrs     \tmp, mdscr_el1
        orr     \tmp, \tmp, #DBG_MDSCR_SS
        msr     mdscr_el1, \tmp