[PATCH v4 4/5] powerpc/code-patching: introduce patch_instructions()

[Hari Bathini <hbathini@linux.ibm.com>]

patch_instruction() entails setting up pte, patching the instruction,
clearing the pte and flushing the tlb. If multiple instructions need
to be patched, every instruction would have to go through the above
drill unnecessarily. Instead, introduce function patch_instructions()
that sets up the pte, clears the pte and flushes the tlb only once per
page range of instructions to be patched. This adds a slight overhead
to patch_instruction() call while improving the patching time for
scenarios where more than one instruction needs to be patched.

Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
---
 arch/powerpc/include/asm/code-patching.h |  1 +
 arch/powerpc/lib/code-patching.c         | 94 ++++++++++++++++++++----
 2 files changed, 80 insertions(+), 15 deletions(-)

diff --git a/arch/powerpc/include/asm/code-patching.h b/arch/powerpc/include/asm/code-patching.h
index 3f881548fb61..4f5f0c091586 100644
--- a/arch/powerpc/include/asm/code-patching.h
+++ b/arch/powerpc/include/asm/code-patching.h
@@ -74,6 +74,7 @@ int create_cond_branch(ppc_inst_t *instr, const u32 *addr,
 int patch_branch(u32 *addr, unsigned long target, int flags);
 int patch_instruction(u32 *addr, ppc_inst_t instr);
 int raw_patch_instruction(u32 *addr, ppc_inst_t instr);
+int patch_instructions(void *addr, void *code, size_t len, bool fill_insn);
 
 static inline unsigned long patch_site_addr(s32 *site)
 {
diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
index b00112d7ad46..60d446e16b42 100644
--- a/arch/powerpc/lib/code-patching.c
+++ b/arch/powerpc/lib/code-patching.c
@@ -278,20 +278,25 @@ static void unmap_patch_area(unsigned long addr)
 	flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
 }
 
-static int __do_patch_instruction_mm(u32 *addr, ppc_inst_t instr)
+/*
+ * A page is mapped and instructions that fit the page are patched.
+ * Assumes 'len' to be (PAGE_SIZE - offset_in_page(addr)) or below.
+ */
+static int __do_patch_instructions_mm(u32 *addr, void *code, size_t len, bool fill_insn)
 {
-	int err;
-	u32 *patch_addr;
 	unsigned long text_poke_addr;
 	pte_t *pte;
 	unsigned long pfn = get_patch_pfn(addr);
 	struct mm_struct *patching_mm;
 	struct mm_struct *orig_mm;
+	ppc_inst_t instr;
+	void *patch_addr;
 	spinlock_t *ptl;
+	int ilen, err;
 
 	patching_mm = __this_cpu_read(cpu_patching_context.mm);
 	text_poke_addr = __this_cpu_read(cpu_patching_context.addr);
-	patch_addr = (u32 *)(text_poke_addr + offset_in_page(addr));
+	patch_addr = (void *)(text_poke_addr + offset_in_page(addr));
 
 	pte = get_locked_pte(patching_mm, text_poke_addr, &ptl);
 	if (!pte)
@@ -307,11 +312,22 @@ static int __do_patch_instruction_mm(u32 *addr, ppc_inst_t instr)
 
 	orig_mm = start_using_temp_mm(patching_mm);
 
-	err = __patch_instruction(addr, instr, patch_addr);
+	while (len > 0) {
+		instr = ppc_inst_read(code);
+		ilen = ppc_inst_len(instr);
+		err = __patch_instruction(addr, instr, patch_addr);
+		/* hwsync performed by __patch_instruction (sync) if successful */
+		if (err) {
+			mb();  /* sync */
+			break;
+		}
 
-	/* hwsync performed by __patch_instruction (sync) if successful */
-	if (err)
-		mb();  /* sync */
+		len -= ilen;
+		patch_addr = patch_addr + ilen;
+		addr = (void *)addr + ilen;
+		if (!fill_insn)
+			code = code + ilen;
+	}
 
 	/* context synchronisation performed by __patch_instruction (isync or exception) */
 	stop_using_temp_mm(patching_mm, orig_mm);
@@ -328,16 +344,21 @@ static int __do_patch_instruction_mm(u32 *addr, ppc_inst_t instr)
 	return err;
 }
 
-static int __do_patch_instruction(u32 *addr, ppc_inst_t instr)
+/*
+ * A page is mapped and instructions that fit the page are patched.
+ * Assumes 'len' to be (PAGE_SIZE - offset_in_page(addr)) or below.
+ */
+static int __do_patch_instructions(u32 *addr, void *code, size_t len, bool fill_insn)
 {
-	int err;
-	u32 *patch_addr;
 	unsigned long text_poke_addr;
 	pte_t *pte;
 	unsigned long pfn = get_patch_pfn(addr);
+	void *patch_addr;
+	ppc_inst_t instr;
+	int ilen, err;
 
 	text_poke_addr = (unsigned long)__this_cpu_read(cpu_patching_context.addr) & PAGE_MASK;
-	patch_addr = (u32 *)(text_poke_addr + offset_in_page(addr));
+	patch_addr = (void *)(text_poke_addr + offset_in_page(addr));
 
 	pte = __this_cpu_read(cpu_patching_context.pte);
 	__set_pte_at(&init_mm, text_poke_addr, pte, pfn_pte(pfn, PAGE_KERNEL), 0);
@@ -345,7 +366,19 @@ static int __do_patch_instruction(u32 *addr, ppc_inst_t instr)
 	if (radix_enabled())
 		asm volatile("ptesync": : :"memory");
 
-	err = __patch_instruction(addr, instr, patch_addr);
+	while (len > 0) {
+		instr = ppc_inst_read(code);
+		ilen = ppc_inst_len(instr);
+		err = __patch_instruction(addr, instr, patch_addr);
+		if (err)
+			break;
+
+		len -= ilen;
+		patch_addr = patch_addr + ilen;
+		addr = (void *)addr + ilen;
+		if (!fill_insn)
+			code = code + ilen;
+	}
 
 	pte_clear(&init_mm, text_poke_addr, pte);
 	flush_tlb_kernel_range(text_poke_addr, text_poke_addr + PAGE_SIZE);
@@ -369,15 +402,46 @@ int patch_instruction(u32 *addr, ppc_inst_t instr)
 
 	local_irq_save(flags);
 	if (mm_patch_enabled())
-		err = __do_patch_instruction_mm(addr, instr);
+		err = __do_patch_instructions_mm(addr, &instr, ppc_inst_len(instr), false);
 	else
-		err = __do_patch_instruction(addr, instr);
+		err = __do_patch_instructions(addr, &instr, ppc_inst_len(instr), false);
 	local_irq_restore(flags);
 
 	return err;
 }
 NOKPROBE_SYMBOL(patch_instruction);
 
+/*
+ * Patch 'addr' with 'len' bytes of instructions from 'code'.
+ */
+int patch_instructions(void *addr, void *code, size_t len, bool fill_insn)
+{
+	unsigned long flags;
+	size_t plen;
+	int err;
+
+	while (len > 0) {
+		plen = min_t(size_t, PAGE_SIZE - offset_in_page(addr), len);
+
+		local_irq_save(flags);
+		if (mm_patch_enabled())
+			err = __do_patch_instructions_mm(addr, code, plen, fill_insn);
+		else
+			err = __do_patch_instructions(addr, code, plen, fill_insn);
+		local_irq_restore(flags);
+		if (err)
+			break;
+
+		len -= plen;
+		addr = addr + plen;
+		if (!fill_insn)
+			code = code + plen;
+	}
+
+	return err;
+}
+NOKPROBE_SYMBOL(patch_instructions);
+
 int patch_branch(u32 *addr, unsigned long target, int flags)
 {
 	ppc_inst_t instr;
-- 
2.41.0