Re: [PATCH bpf-next v3 1/3] riscv: extend patch_text_nosync() for multiple pages

[Pu Lehui]

On 2023/8/29 0:59, Puranjay Mohan wrote:
> The patch_insn_write() function currently doesn't work for multiple pages
> of instructions, therefore patch_text_nosync() will fail with a page fault
> if called with lengths spanning multiple pages.
>
> This commit extends the patch_insn_write() function to support multiple
> pages by copying at max 2 pages at a time in a loop. This implementation
> is similar to text_poke_copy() function of x86.
>
> Signed-off-by: Puranjay Mohan <puranjay12@xxxxxxxxx>
> Reviewed-by: Björn Töpel <bjorn@xxxxxxxxxxxx>
> ---
>   arch/riscv/kernel/patch.c | 37 ++++++++++++++++++++++++++++++++-----
>   1 file changed, 32 insertions(+), 5 deletions(-)
>
> diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
> index 575e71d6c8ae..2c97e246f4dc 100644
> --- a/arch/riscv/kernel/patch.c
> +++ b/arch/riscv/kernel/patch.c
> @@ -53,12 +53,18 @@ static void patch_unmap(int fixmap)
>   }
>   NOKPROBE_SYMBOL(patch_unmap);
>   
> -static int patch_insn_write(void *addr, const void *insn, size_t len)
> +static int __patch_insn_write(void *addr, const void *insn, size_t len)
>   {
>   	void *waddr = addr;
>   	bool across_pages = (((uintptr_t) addr & ~PAGE_MASK) + len) > PAGE_SIZE;
>   	int ret;
>   
> +	/*
> +	 * Only two pages can be mapped at a time for writing.
> +	 */
> +	if (len + offset_in_page(addr) > 2 * PAGE_SIZE)
> +		return -EINVAL;
> +
>   	/*
>   	 * Before reaching here, it was expected to lock the text_mutex
>   	 * already, so we don't need to give another lock here and could
> @@ -74,7 +80,7 @@ static int patch_insn_write(void *addr, const void *insn, size_t len)
>   		lockdep_assert_held(&text_mutex);
>   
>   	if (across_pages)
> -		patch_map(addr + len, FIX_TEXT_POKE1);
> +		patch_map(addr + PAGE_SIZE, FIX_TEXT_POKE1);
>   
>   	waddr = patch_map(addr, FIX_TEXT_POKE0);
>   
> @@ -87,15 +93,36 @@ static int patch_insn_write(void *addr, const void *insn, size_t len)
>   
>   	return ret;
>   }
> -NOKPROBE_SYMBOL(patch_insn_write);
> +NOKPROBE_SYMBOL(__patch_insn_write);
>   #else
> -static int patch_insn_write(void *addr, const void *insn, size_t len)
> +static int __patch_insn_write(void *addr, const void *insn, size_t len)
>   {
>   	return copy_to_kernel_nofault(addr, insn, len);
>   }
> -NOKPROBE_SYMBOL(patch_insn_write);
> +NOKPROBE_SYMBOL(__patch_insn_write);
>   #endif /* CONFIG_MMU */
>   
> +static int patch_insn_write(void *addr, const void *insn, size_t len)
> +{
> +	size_t patched = 0;
> +	size_t size;
> +	int ret = 0;
> +
> +	/*
> +	 * Copy the instructions to the destination address, two pages at a time
> +	 * because __patch_insn_write() can only handle len <= 2 * PAGE_SIZE.
> +	 */
> +	while (patched < len && !ret) {
> +		size = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(addr + patched), len - patched);
> +		ret = __patch_insn_write(addr + patched, insn + patched, size);
> +
> +		patched += size;
> +	}
> +
> +	return ret;
> +}
> +NOKPROBE_SYMBOL(patch_insn_write);
> +
>   int patch_text_nosync(void *addr, const void *insns, size_t len)
>   {
>   	u32 *tp = addr;

Looks good to me,
Reviewed-by: Pu Lehui <pulehui@xxxxxxxxxx>