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

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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@xxxxxxxxxxxxx>
> ---
>   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@xxxxxxxxxx/

> +	} 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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