Re: [PATCH v3 1/5] powerpc/bpf: implement bpf_arch_text_copy

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 25/08/2023 à 17:18, Hari Bathini a écrit :
> bpf_arch_text_copy is used to dump JITed binary to RX page, allowing
> multiple BPF programs to share the same page. Use patch_instruction()
> to implement it.

By using patch_instruction() for doing that you are mapping and 
unmapping the same page for each instruction you copy. You should 
implement something to map a page, copy all instruction going into that 
page, unmap the page and map next page, etc ....
And then perform the icache flush at the end.

> 
> Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
> ---
>   arch/powerpc/net/bpf_jit_comp.c | 40 ++++++++++++++++++++++++++++++++-
>   1 file changed, 39 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
> index 37043dfc1add..170ebf8ac0f2 100644
> --- a/arch/powerpc/net/bpf_jit_comp.c
> +++ b/arch/powerpc/net/bpf_jit_comp.c
> @@ -13,9 +13,12 @@
>   #include <linux/netdevice.h>
>   #include <linux/filter.h>
>   #include <linux/if_vlan.h>
> -#include <asm/kprobes.h>
> +#include <linux/memory.h>
>   #include <linux/bpf.h>
>   
> +#include <asm/kprobes.h>
> +#include <asm/code-patching.h>
> +
>   #include "bpf_jit.h"
>   
>   static void bpf_jit_fill_ill_insns(void *area, unsigned int size)
> @@ -23,6 +26,27 @@ static void bpf_jit_fill_ill_insns(void *area, unsigned int size)
>   	memset32(area, BREAKPOINT_INSTRUCTION, size / 4);
>   }
>   
> +/*
> + * Patch 'len' bytes of instructions from opcode to addr, one instruction
> + * at a time. Returns addr on success. ERR_PTR(-EINVAL), otherwise.
> + */
> +static void *bpf_patch_instructions(void *addr, void *opcode, size_t len)
> +{
> +	while (len > 0) {
> +		ppc_inst_t insn = ppc_inst_read(opcode);
> +		int ilen = ppc_inst_len(insn);
> +
> +		if (patch_instruction(addr, insn))
> +			return ERR_PTR(-EINVAL);
> +
> +		len -= ilen;
> +		addr = addr + ilen;
> +		opcode = opcode + ilen;
> +	}
> +
> +	return addr;
> +}
> +
>   int bpf_jit_emit_exit_insn(u32 *image, struct codegen_context *ctx, int tmp_reg, long exit_addr)
>   {
>   	if (!exit_addr || is_offset_in_branch_range(exit_addr - (ctx->idx * 4))) {
> @@ -274,3 +298,17 @@ int bpf_add_extable_entry(struct bpf_prog *fp, u32 *image, int pass, struct code
>   	ctx->exentry_idx++;
>   	return 0;
>   }
> +
> +void *bpf_arch_text_copy(void *dst, void *src, size_t len)
> +{
> +	void *ret;
> +
> +	if (WARN_ON_ONCE(core_kernel_text((unsigned long)dst)))
> +		return ERR_PTR(-EINVAL);
> +
> +	mutex_lock(&text_mutex);
> +	ret = bpf_patch_instructions(dst, src, len);
> +	mutex_unlock(&text_mutex);
> +
> +	return ret;
> +}