s390: remove unused expoline to BC instructions

This reverts commit 6deaa3bbca80 ("s390: extend expoline to BC
instructions"). Expolines to BC instructions were added to be utilized
by commit de5cb6eb514e ("s390: use expoline thunks in the BPF JIT"). But
corresponding code has been removed by commit e1cf4befa297 ("bpf, s390x:
remove ld_abs/ld_ind"). And compiler does not generate such expolines as
well.

Compared to regular expolines, expolines to BC instructions contain
displacement and all possible variations cannot be generated in advance,
making kpatch support more complicated. So, remove those to avoid
future usages.

Acked-by: Heiko Carstens <hca@linux.ibm.com>
Acked-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

1 files changed, 5 insertions, 20 deletions

diff --git a/arch/s390/kernel/nospec-branch.c b/arch/s390/kernel/nospec-branch.c
index 60e6fec27bba..c302e0a7d38f 100644
--- a/arch/s390/kernel/nospec-branch.c
+++ b/arch/s390/kernel/nospec-branch.c
@@ -105,6 +105,7 @@ static void __init_or_module __nospec_revert(s32 *start, s32 *end)
 	s32 *epo;
 
 	/* Second part of the instruction replace is always a nop */
+	memcpy(insnbuf + 2, branch, sizeof(branch));
 	for (epo = start; epo < end; epo++) {
 		instr = (u8 *) epo + *epo;
 		if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x04)
@@ -125,34 +126,18 @@ static void __init_or_module __nospec_revert(s32 *start, s32 *end)
 			br = thunk + (*(int *)(thunk + 2)) * 2;
 		else
 			continue;
-		/* Check for unconditional branch 0x07f? or 0x47f???? */
-		if ((br[0] & 0xbf) != 0x07 || (br[1] & 0xf0) != 0xf0)
+		if (br[0] != 0x07 || (br[1] & 0xf0) != 0xf0)
 			continue;
-
-		memcpy(insnbuf + 2, branch, sizeof(branch));
 		switch (type) {
 		case BRCL_EXPOLINE:
+			/* brcl to thunk, replace with br + nop */
 			insnbuf[0] = br[0];
 			insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
-			if (br[0] == 0x47) {
-				/* brcl to b, replace with bc + nopr */
-				insnbuf[2] = br[2];
-				insnbuf[3] = br[3];
-			} else {
-				/* brcl to br, replace with bcr + nop */
-			}
 			break;
 		case BRASL_EXPOLINE:
+			/* brasl to thunk, replace with basr + nop */
+			insnbuf[0] = 0x0d;
 			insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
-			if (br[0] == 0x47) {
-				/* brasl to b, replace with bas + nopr */
-				insnbuf[0] = 0x4d;
-				insnbuf[2] = br[2];
-				insnbuf[3] = br[3];
-			} else {
-				/* brasl to br, replace with basr + nop */
-				insnbuf[0] = 0x0d;
-			}
 			break;
 		}