[tip: x86/core] x86/ibt,paravirt: Use text_gen_insn() for paravirt_patch()

[tip-bot2 for Peter Zijlstra]

The following commit has been merged into the x86/core branch of tip:

Commit-ID:     7fb70b6975509102d848f1abdba394e0bdc122c1
Gitweb:        https://git.kernel.org/tip/7fb70b6975509102d848f1abdba394e0bdc122c1
Author:        Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate:    Tue, 08 Mar 2022 16:30:20 +01:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Tue, 08 Mar 2022 23:53:28 +01:00

x86/ibt,paravirt: Use text_gen_insn() for paravirt_patch()

Less duplication is more better.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Acked-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20220308154317.697253958@xxxxxxxxxxxxx
---
 arch/x86/include/asm/text-patching.h | 20 ++++++++++++++------
 arch/x86/kernel/paravirt.c           | 23 +++--------------------
 2 files changed, 17 insertions(+), 26 deletions(-)

diff --git a/arch/x86/include/asm/text-patching.h b/arch/x86/include/asm/text-patching.h
index 1c4cfb1..c6015b4 100644
--- a/arch/x86/include/asm/text-patching.h
+++ b/arch/x86/include/asm/text-patching.h
@@ -96,32 +96,40 @@ union text_poke_insn {
 };
 
 static __always_inline
-void *text_gen_insn(u8 opcode, const void *addr, const void *dest)
+void __text_gen_insn(void *buf, u8 opcode, const void *addr, const void *dest, int size)
 {
-	static union text_poke_insn insn; /* per instance */
-	int size = text_opcode_size(opcode);
+	union text_poke_insn *insn = buf;
+
+	BUG_ON(size < text_opcode_size(opcode));
 
 	/*
 	 * Hide the addresses to avoid the compiler folding in constants when
 	 * referencing code, these can mess up annotations like
 	 * ANNOTATE_NOENDBR.
 	 */
+	OPTIMIZER_HIDE_VAR(insn);
 	OPTIMIZER_HIDE_VAR(addr);
 	OPTIMIZER_HIDE_VAR(dest);
 
-	insn.opcode = opcode;
+	insn->opcode = opcode;
 
 	if (size > 1) {
-		insn.disp = (long)dest - (long)(addr + size);
+		insn->disp = (long)dest - (long)(addr + size);
 		if (size == 2) {
 			/*
 			 * Ensure that for JMP8 the displacement
 			 * actually fits the signed byte.
 			 */
-			BUG_ON((insn.disp >> 31) != (insn.disp >> 7));
+			BUG_ON((insn->disp >> 31) != (insn->disp >> 7));
 		}
 	}
+}
 
+static __always_inline
+void *text_gen_insn(u8 opcode, const void *addr, const void *dest)
+{
+	static union text_poke_insn insn; /* per instance */
+	__text_gen_insn(&insn, opcode, addr, dest, text_opcode_size(opcode));
 	return &insn.text;
 }
 
diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index 4420499..06af2cf 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -69,29 +69,12 @@ noinstr void paravirt_BUG(void)
 	BUG();
 }
 
-struct branch {
-	unsigned char opcode;
-	u32 delta;
-} __attribute__((packed));
-
 static unsigned paravirt_patch_call(void *insn_buff, const void *target,
 				    unsigned long addr, unsigned len)
 {
-	const int call_len = 5;
-	struct branch *b = insn_buff;
-	unsigned long delta = (unsigned long)target - (addr+call_len);
-
-	if (len < call_len) {
-		pr_warn("paravirt: Failed to patch indirect CALL at %ps\n", (void *)addr);
-		/* Kernel might not be viable if patching fails, bail out: */
-		BUG_ON(1);
-	}
-
-	b->opcode = 0xe8; /* call */
-	b->delta = delta;
-	BUILD_BUG_ON(sizeof(*b) != call_len);
-
-	return call_len;
+	__text_gen_insn(insn_buff, CALL_INSN_OPCODE,
+			(void *)addr, target, CALL_INSN_SIZE);
+	return CALL_INSN_SIZE;
 }
 
 #ifdef CONFIG_PARAVIRT_XXL