[PATCH v1 2/4] powerpc/code-patching: Speed up page mapping/unmapping

[Christophe Leroy]

Since commit 591b4b268435 ("powerpc/code-patching: Pre-map patch area")
the patch area is premapped so intermediate page tables are already
allocated.

Use __set_pte_at() directly instead of the heavy map_kernel_page(),
at for unmapping just do a pte_clear() followed by a flush.

__set_pte_at() can be used directly without the filters in
set_pte_at() because we are mapping a normal page non executable.

Make sure gcc knows text_poke_area is page aligned in order to
optimise the flush.

This change reduces by 66% the time needed to activate ftrace on
an 8xx (588000 tb ticks instead of 1744000).

Signed-off-by: Christophe Leroy <christophe.le...@csgroup.eu>
---
 arch/powerpc/lib/code-patching.c | 27 ++++++++++++++++-----------
 1 file changed, 16 insertions(+), 11 deletions(-)

diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
index f970f189875b..62692c6031bc 100644
--- a/arch/powerpc/lib/code-patching.c
+++ b/arch/powerpc/lib/code-patching.c
@@ -90,17 +90,20 @@ void __init poking_init(void)
                text_area_cpu_down));
 }
 
+static unsigned long get_patch_pfn(void *addr)
+{
+       if (IS_ENABLED(CONFIG_MODULES) && is_vmalloc_or_module_addr(addr))
+               return vmalloc_to_pfn(addr);
+       else
+               return __pa_symbol(addr) >> PAGE_SHIFT;
+}
+
 /*
  * This can be called for kernel text or a module.
  */
 static int map_patch_area(void *addr, unsigned long text_poke_addr)
 {
-       unsigned long pfn;
-
-       if (IS_ENABLED(CONFIG_MODULES) && is_vmalloc_or_module_addr(addr))
-               pfn = vmalloc_to_pfn(addr);
-       else
-               pfn = __pa_symbol(addr) >> PAGE_SHIFT;
+       unsigned long pfn = get_patch_pfn(addr);
 
        return map_kernel_page(text_poke_addr, (pfn << PAGE_SHIFT), 
PAGE_KERNEL);
 }
@@ -145,17 +148,19 @@ static int __do_patch_instruction(u32 *addr, ppc_inst_t 
instr)
        int err;
        u32 *patch_addr;
        unsigned long text_poke_addr;
+       pte_t *pte;
+       unsigned long pfn = get_patch_pfn(addr);
 
-       text_poke_addr = (unsigned long)__this_cpu_read(text_poke_area)->addr;
+       text_poke_addr = (unsigned long)__this_cpu_read(text_poke_area)->addr & 
PAGE_MASK;
        patch_addr = (u32 *)(text_poke_addr + offset_in_page(addr));
 
-       err = map_patch_area(addr, text_poke_addr);
-       if (err)
-               return err;
+       pte = virt_to_kpte(text_poke_addr);
+       __set_pte_at(&init_mm, text_poke_addr, pte, pfn_pte(pfn, PAGE_KERNEL), 
0);
 
        err = __patch_instruction(addr, instr, patch_addr);
 
-       unmap_patch_area(text_poke_addr);
+       pte_clear(&init_mm, text_poke_addr, pte);
+       flush_tlb_kernel_range(text_poke_addr, text_poke_addr + PAGE_SIZE);
 
        return err;
 }
-- 
2.35.1