FAILED: patch "[PATCH] powerpc/sstep: Fix incorrect return from analyze_instr()" failed to apply to 5.4-stable tree

The patch below does not apply to the 5.4-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to [off-list ref].

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 718aae916fa6619c57c348beaedd675835cf1aa1 Mon Sep 17 00:00:00 2001
From: Ananth N Mavinakayanahalli <redacted>
Date: Mon, 25 Jan 2021 18:36:43 +0530
Subject: [PATCH] powerpc/sstep: Fix incorrect return from analyze_instr()

We currently just percolate the return value from analyze_instr()
to the caller of emulate_step(), especially if it is a -1.

For one particular case (opcode = 4) for instructions that aren't
currently emulated, we are returning 'should not be single-stepped'
while we should have returned 0 which says 'did not emulate, may
have to single-step'.

Fixes: 930d6288a26787 ("powerpc: sstep: Add support for maddhd, maddhdu, maddld instructions")
Signed-off-by: Ananth N Mavinakayanahalli <redacted>
Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
Tested-by: Naveen N. Rao <redacted>
Reviewed-by: Sandipan Das <redacted>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/161157999039.64773.14950289716779364766.stgit@thinktux.local (local)

diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
index f859cbbb6375..e96cff845ef7 100644
--- a/arch/powerpc/lib/sstep.c
+++ b/arch/powerpc/lib/sstep.c

@@ -1445,6 +1445,11 @@ int analyse_instr(struct instruction_op *op, const struct pt_regs *regs,
 
 #ifdef __powerpc64__
 	case 4:
+		/*
+		 * There are very many instructions with this primary opcode
+		 * introduced in the ISA as early as v2.03. However, the ones
+		 * we currently emulate were all introduced with ISA 3.0
+		 */
 		if (!cpu_has_feature(CPU_FTR_ARCH_300))
 			goto unknown_opcode;
 

@@ -1472,7 +1477,7 @@ int analyse_instr(struct instruction_op *op, const struct pt_regs *regs,
 		 * There are other instructions from ISA 3.0 with the same
 		 * primary opcode which do not have emulation support yet.
 		 */
-		return -1;
+		goto unknown_opcode;
 #endif
 
 	case 7:		/* mulli */