Subject: [PATCH v10 9/9] powerpc/code-patching: Consolidate and cache per-cpu patching context

From: Benjamin Gray <[email-masked]>
Date: Wed, 9 Nov 2022 15:51:12 +1100

With the temp mm context support, there are CPU local variables to hold
the patch address and pte. Use these in the non-temp mm path as well
instead of adding a level of indirection through the text_poke_area
vm_struct and pointer chasing the pte.

As both paths use these fields now, there is no need to let unreferenced
variables be dropped by the compiler, so it is cleaner to merge them into
a single context struct. This has the additional benefit of removing a
redundant CPU local pointer, as only one of cpu_patching_mm /
text_poke_area is ever used, while remaining well-typed. It also groups
each CPU's data into a single cacheline.

Signed-off-by: Benjamin Gray <[email-masked]>
---
v10:	* Mention cache benefits
v9:	* Consolidate patching context into single struct
---
 arch/powerpc/lib/code-patching.c | 49 +++++++++++++++++++-------------
 1 file changed, 30 insertions(+), 19 deletions(-)

diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
index 5b0022997296..2e10df464a2b 100644
--- a/arch/powerpc/lib/code-patching.c
+++ b/arch/powerpc/lib/code-patching.c
@@ -48,10 +48,16 @@ int raw_patch_instruction(u32 *addr, ppc_inst_t instr)
 
 #ifdef CONFIG_STRICT_KERNEL_RWX
 
-static DEFINE_PER_CPU(struct vm_struct *, text_poke_area);
-static DEFINE_PER_CPU(struct mm_struct *, cpu_patching_mm);
-static DEFINE_PER_CPU(unsigned long, cpu_patching_addr);
-static DEFINE_PER_CPU(pte_t *, cpu_patching_pte);
+struct patch_context {
+	union {
+		struct vm_struct *text_poke_area;
+		struct mm_struct *mm;
+	};
+	unsigned long addr;
+	pte_t * pte;
+};
+
+static DEFINE_PER_CPU(struct patch_context, cpu_patching_context);
 
 static int map_patch_area(void *addr, unsigned long text_poke_addr);
 static void unmap_patch_area(unsigned long addr);
@@ -116,14 +122,19 @@ static int text_area_cpu_up(unsigned int cpu)
 
 	unmap_patch_area(addr);
 
-	this_cpu_write(text_poke_area, area);
+	this_cpu_write(cpu_patching_context.text_poke_area, area);
+	this_cpu_write(cpu_patching_context.addr, addr);
+	this_cpu_write(cpu_patching_context.pte, virt_to_kpte(addr));
 
 	return 0;
 }
 
 static int text_area_cpu_down(unsigned int cpu)
 {
-	free_vm_area(this_cpu_read(text_poke_area));
+	free_vm_area(this_cpu_read(cpu_patching_context.text_poke_area));
+	this_cpu_write(cpu_patching_context.text_poke_area, NULL);
+	this_cpu_write(cpu_patching_context.addr, 0);
+	this_cpu_write(cpu_patching_context.pte, NULL);
 	return 0;
 }
 
@@ -167,9 +178,9 @@ static int text_area_cpu_up_mm(unsigned int cpu)
 		goto fail_no_pte;
 	pte_unmap_unlock(pte, ptl);
 
-	this_cpu_write(cpu_patching_mm, mm);
-	this_cpu_write(cpu_patching_addr, addr);
-	this_cpu_write(cpu_patching_pte, pte);
+	this_cpu_write(cpu_patching_context.mm, mm);
+	this_cpu_write(cpu_patching_context.addr, addr);
+	this_cpu_write(cpu_patching_context.pte, pte);
 
 	return 0;
 
@@ -181,12 +192,12 @@ static int text_area_cpu_up_mm(unsigned int cpu)
 
 static int text_area_cpu_down_mm(unsigned int cpu)
 {
-	put_patching_mm(this_cpu_read(cpu_patching_mm),
-			this_cpu_read(cpu_patching_addr));
+	put_patching_mm(this_cpu_read(cpu_patching_context.mm),
+			this_cpu_read(cpu_patching_context.addr));
 
-	this_cpu_write(cpu_patching_mm, NULL);
-	this_cpu_write(cpu_patching_addr, 0);
-	this_cpu_write(cpu_patching_pte, NULL);
+	this_cpu_write(cpu_patching_context.mm, NULL);
+	this_cpu_write(cpu_patching_context.addr, 0);
+	this_cpu_write(cpu_patching_context.pte, NULL);
 
 	return 0;
 }
@@ -278,9 +289,9 @@ static int __do_patch_instruction_mm(u32 *addr, ppc_inst_t instr)
 	struct mm_struct *patching_mm;
 	struct mm_struct *orig_mm;
 
-	patching_mm = __this_cpu_read(cpu_patching_mm);
-	pte = __this_cpu_read(cpu_patching_pte);
-	text_poke_addr = __this_cpu_read(cpu_patching_addr);
+	patching_mm = __this_cpu_read(cpu_patching_context.mm);
+	pte = __this_cpu_read(cpu_patching_context.pte);
+	text_poke_addr = __this_cpu_read(cpu_patching_context.addr);
 	patch_addr = (u32 *)(text_poke_addr + offset_in_page(addr));
 
 	__set_pte_at(patching_mm, text_poke_addr, pte, pfn_pte(pfn, PAGE_KERNEL), 0);
@@ -320,10 +331,10 @@ static int __do_patch_instruction(u32 *addr, ppc_inst_t instr)
 	pte_t *pte;
 	unsigned long pfn = get_patch_pfn(addr);
 
-	text_poke_addr = (unsigned long)__this_cpu_read(text_poke_area)->addr & PAGE_MASK;
+	text_poke_addr = (unsigned long)__this_cpu_read(cpu_patching_context.addr) & PAGE_MASK;
 	patch_addr = (u32 *)(text_poke_addr + offset_in_page(addr));
 
-	pte = virt_to_kpte(text_poke_addr);
+	pte = __this_cpu_read(cpu_patching_context.pte);
 	__set_pte_at(&init_mm, text_poke_addr, pte, pfn_pte(pfn, PAGE_KERNEL), 0);
 	/* See ptesync comment in radix__set_pte_at() */
 	if (radix_enabled())
-- 
2.38.1