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Subject[PATCH v1 2/4] powerpc/code-patching: Speed up page mapping/unmapping
Date
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.leroy@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
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