s390: remove unused expoline to BC instructions

This reverts commit 6deaa3bbca ("s390: extend expoline to BC
instructions"). Expolines to BC instructions were added to be utilized
by commit de5cb6eb51 ("s390: use expoline thunks in the BPF JIT"). But
corresponding code has been removed by commit e1cf4befa2 ("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>

arch/s390/include/asm/nospec-insn.h

@@ -35,18 +35,10 @@ _LC_BR_R1 = __LC_BR_R1
 	__THUNK_PROLOG_NAME __s390_indirect_jump_r\r2\()use_r\r1
 	.endm
 
-	.macro __THUNK_PROLOG_BC d0,r1,r2
-	__THUNK_PROLOG_NAME __s390_indirect_branch_\d0\()_\r2\()use_\r1
-	.endm
-
 	.macro __THUNK_BR r1,r2
 	jg	__s390_indirect_jump_r\r2\()use_r\r1
 	.endm
 
-	.macro __THUNK_BC d0,r1,r2
-	jg	__s390_indirect_branch_\d0\()_\r2\()use_\r1
-	.endm
-
 	.macro __THUNK_BRASL r1,r2,r3
 	brasl	\r1,__s390_indirect_jump_r\r3\()use_r\r2
 	.endm
@@ -89,23 +81,6 @@ _LC_BR_R1 = __LC_BR_R1
 	.endif
 	.endm
 
-	.macro	__DECODE_DRR expand,disp,reg,ruse
-	.set __decode_fail,1
-	.irp r1,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
-	.ifc \reg,%r\r1
-	.irp r2,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
-	.ifc \ruse,%r\r2
-	\expand \disp,\r1,\r2
-	.set __decode_fail,0
-	.endif
-	.endr
-	.endif
-	.endr
-	.if __decode_fail == 1
-	.error "__DECODE_DRR failed"
-	.endif
-	.endm
-
 	.macro __THUNK_EX_BR reg,ruse
 	# Be very careful when adding instructions to this macro!
 	# The ALTERNATIVE replacement code has a .+10 which targets
@@ -126,42 +101,17 @@ _LC_BR_R1 = __LC_BR_R1
 555:	br	\reg
 	.endm
 
-	.macro __THUNK_EX_BC disp,reg,ruse
-#ifdef CONFIG_HAVE_MARCH_Z10_FEATURES
-	exrl	0,556f
-	j	.
-#else
-	larl	\ruse,556f
-	ex	0,0(\ruse)
-	j	.
-#endif
-556:	b	\disp(\reg)
-	.endm
-
 	.macro GEN_BR_THUNK reg,ruse=%r1
 	__DECODE_RR __THUNK_PROLOG_BR,\reg,\ruse
 	__THUNK_EX_BR \reg,\ruse
 	__THUNK_EPILOG
 	.endm
 
-	.macro GEN_B_THUNK disp,reg,ruse=%r1
-	__DECODE_DRR __THUNK_PROLOG_BC,\disp,\reg,\ruse
-	__THUNK_EX_BC \disp,\reg,\ruse
-	__THUNK_EPILOG
-	.endm
-
 	.macro BR_EX reg,ruse=%r1
 557:	__DECODE_RR __THUNK_BR,\reg,\ruse
 	.pushsection .s390_indirect_branches,"a",@progbits
 	.long	557b-.
 	.popsection
-	.endm
-
-	 .macro B_EX disp,reg,ruse=%r1
-558:	__DECODE_DRR __THUNK_BC,\disp,\reg,\ruse
-	.pushsection .s390_indirect_branches,"a",@progbits
-	.long	558b-.
-	.popsection
 	.endm
 
 	.macro BASR_EX rsave,rtarget,ruse=%r1
@@ -173,17 +123,10 @@ _LC_BR_R1 = __LC_BR_R1
 
 #else
 	.macro GEN_BR_THUNK reg,ruse=%r1
-	.endm
-
-	.macro GEN_B_THUNK disp,reg,ruse=%r1
 	.endm
 
 	 .macro BR_EX reg,ruse=%r1
 	br	\reg
-	.endm
-
-	 .macro B_EX disp,reg,ruse=%r1
-	b	\disp(\reg)
 	.endm
 
 	.macro BASR_EX rsave,rtarget,ruse=%r1

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;
 		}