[PATCH v5 1/5] powerpc/code-patching: introduce patch_instructions()

[Song Liu]

On Thu, Sep 28, 2023 at 12:48 PM Hari Bathini <hbathini at linux.ibm.com> wrote:
>
> 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 at linux.ibm.com>

Acked-by: Song Liu <song at kernel.org>

With a nit below.

[...]
> +/*
> + * 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);

len == 0 for single instruction is a little weird to me. How about we just use
len == 4 or 8 depending on the instruction to patch?

Thanks,
Song

[...]