arm64: entry: handle debug exceptions in el*_inv

Currently we enable debug exceptions before reading ESR_EL1 in both
el0_inv and el1_inv. If a debug exception is taken before we read
ESR_EL1, the value will have been corrupted.

As el*_inv is typically fatal, an intervening debug exception results in
misleading debug information being logged to the console, but is not
otherwise harmful.

As with the other entry paths, we can use the ESR_EL1 value stashed
earlier in the exception entry (in x25 for el0_sync{,_compat}, and x1
for el1_sync), giving us better error reporting in this case.
Signed-off-by: NMark Rutland <mark.rutland@arm.com>
Acked-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/entry.S

@@ -352,8 +352,8 @@ el1_inv:
 	// TODO: add support for undefined instructions in kernel mode
 	enable_dbg
 	mov	x0, sp
+	mov	x2, x1
 	mov	x1, #BAD_SYNC
-	mrs	x2, esr_el1
 	b	bad_mode
 ENDPROC(el1_sync)
 
@@ -553,7 +553,7 @@ el0_inv:
 	ct_user_exit
 	mov	x0, sp
 	mov	x1, #BAD_SYNC
-	mrs	x2, esr_el1
+	mov	x2, x25
 	bl	bad_mode
 	b	ret_to_user
 ENDPROC(el0_sync)