[PATCH v5 1/5] powerpc/code-patching: introduce patch_instructions()
Christophe Leroy
christophe.leroy at csgroup.eu
Wed Oct 11 04:46:41 AEDT 2023
Le 28/09/2023 à 21:48, Hari Bathini a écrit :
> 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.
Not a "slight" but a "significant" overhead on PPC32.
Thinking about it once more I don't think it is a good idea to try and
merge that into the existing code_patching logic which is really single
instruction performance oriented.
Anyway, comments below.
>
> Signed-off-by: Hari Bathini <hbathini at linux.ibm.com>
> ---
> arch/powerpc/include/asm/code-patching.h | 1 +
> arch/powerpc/lib/code-patching.c | 93 +++++++++++++++++++++---
> 2 files changed, 85 insertions(+), 9 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/code-patching.h b/arch/powerpc/include/asm/code-patching.h
> index 3f881548fb61..43a4aedfa703 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 repeat_instr);
I don't like void *, you can do to much nasty things with that.
I think you want u32 *
>
> 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..4ff002bc41f6 100644
> --- a/arch/powerpc/lib/code-patching.c
> +++ b/arch/powerpc/lib/code-patching.c
> @@ -278,7 +278,36 @@ 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)
> +static int __patch_instructions(u32 *patch_addr, void *code, size_t len, bool repeat_instr)
> +{
> + unsigned long start = (unsigned long)patch_addr;
> +
> + /* Repeat instruction */
> + if (repeat_instr) {
> + ppc_inst_t instr = ppc_inst_read(code);
> +
> + if (ppc_inst_prefixed(instr)) {
> + u64 val = ppc_inst_as_ulong(instr);
> +
> + memset64((uint64_t *)patch_addr, val, len / 8);
Use u64 instead of uint64_t.
> + } else {
> + u32 val = ppc_inst_val(instr);
> +
> + memset32(patch_addr, val, len / 4);
> + }
> + } else
> + memcpy(patch_addr, code, len);
Missing braces, see
https://docs.kernel.org/process/coding-style.html#placing-braces-and-spaces
> +
> + smp_wmb(); /* smp write barrier */
> + flush_icache_range(start, start + len);
> + return 0;
> +}
> +
> +/*
> + * 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 repeat_instr)
> {
> int err;
> u32 *patch_addr;
> @@ -307,11 +336,15 @@ 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);
> + /* Single instruction case. */
> + if (len == 0) {
> + err = __patch_instruction(addr, *(ppc_inst_t *)code, patch_addr);
Take care, you can't convert u32 * to ppc_inst_t that way, you have to
use ppc_inst_read() otherwise you'll get odd result with prefixed
instructions depending on endianness.
>
> - /* hwsync performed by __patch_instruction (sync) if successful */
> - if (err)
> - mb(); /* sync */
> + /* hwsync performed by __patch_instruction (sync) if successful */
> + if (err)
> + mb(); /* sync */
Get this away, see my patch at
https://patchwork.ozlabs.org/project/linuxppc-dev/patch/e88b154eaf2efd9ff177d472d3411dcdec8ff4f5.1696675567.git.christophe.leroy@csgroup.eu/
> + } else
> + err = __patch_instructions(patch_addr, code, len, repeat_instr);
>
> /* context synchronisation performed by __patch_instruction (isync or exception) */
> stop_using_temp_mm(patching_mm, orig_mm);
> @@ -328,7 +361,11 @@ 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 repeat_instr)
> {
> int err;
> u32 *patch_addr;
> @@ -345,7 +382,11 @@ 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);
> + /* Single instruction case. */
> + if (len == 0)
> + err = __patch_instruction(addr, *(ppc_inst_t *)code, patch_addr);
Same, use ppc_inst_read() instead of this nasty casting.
> + else
> + err = __patch_instructions(patch_addr, code, len, repeat_instr);
>
> pte_clear(&init_mm, text_poke_addr, pte);
> flush_tlb_kernel_range(text_poke_addr, text_poke_addr + PAGE_SIZE);
> @@ -369,15 +410,49 @@ 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, 0, false);
> else
> - err = __do_patch_instruction(addr, instr);
> + err = __do_patch_instructions(addr, &instr, 0, false);
> local_irq_restore(flags);
>
> return err;
> }
> NOKPROBE_SYMBOL(patch_instruction);
>
> +/*
> + * Patch 'addr' with 'len' bytes of instructions from 'code'.
> + *
> + * If repeat_instr is true, the same instruction is filled for
> + * 'len' bytes.
> + */
> +int patch_instructions(void *addr, void *code, size_t len, bool repeat_instr)
I'd like to see code as a u32 *
> +{
> + unsigned long flags;
> + size_t plen;
> + int err;
Move those three variables inside the only block in which they are used.
> +
> + 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, repeat_instr);
> + else
> + err = __do_patch_instructions(addr, code, plen, repeat_instr);
> + local_irq_restore(flags);
> + if (err)
> + break;
replace by 'return err'
> +
> + len -= plen;
> + addr = addr + plen;
> + if (!repeat_instr)
> + code = code + plen;
> + }
> +
> + return err;
If len is 0 err will be undefined. Is that expected ?
Replace by return 0;
> +}
> +NOKPROBE_SYMBOL(patch_instructions);
> +
> int patch_branch(u32 *addr, unsigned long target, int flags)
> {
> ppc_inst_t instr;
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