linux-kernel - Re: [PATCH bpf-next v5 1/3] arm64: patching: Add aarch64_insn

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Message-ID: <mb61pil83a94x.fsf@gmail.com>
Date:   Thu, 21 Sep 2023 14:33:34 +0000
From:   Puranjay Mohan <puranjay12@...il.com>
To:     Xu Kuohai <xukuohai@...weicloud.com>, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org, martin.lau@...ux.dev,
        song@...nel.org, catalin.marinas@....com, mark.rutland@....com,
        bpf@...r.kernel.org, kpsingh@...nel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v5 1/3] arm64: patching: Add aarch64_insn_copy()

Xu Kuohai <xukuohai@...weicloud.com> writes:

> On 9/8/2023 10:43 PM, Puranjay Mohan wrote:
>> This will be used by BPF JIT compiler to dump JITed binary to a RX huge
>> page, and thus allow multiple BPF programs sharing the a huge (2MB)
>> page.
>> 
>> The bpf_prog_pack allocator that implements the above feature allocates
>> a RX/RW buffer pair. The JITed code is written to the RW buffer and then
>> this function will be used to copy the code from RW to RX buffer.
>> 
>> Signed-off-by: Puranjay Mohan <puranjay12@...il.com>
>> Acked-by: Song Liu <song@...nel.org>
>> ---
>>   arch/arm64/include/asm/patching.h |  1 +
>>   arch/arm64/kernel/patching.c      | 41 +++++++++++++++++++++++++++++++
>>   2 files changed, 42 insertions(+)
>> 
>> diff --git a/arch/arm64/include/asm/patching.h b/arch/arm64/include/asm/patching.h
>> index 68908b82b168..f78a0409cbdb 100644
>> --- a/arch/arm64/include/asm/patching.h
>> +++ b/arch/arm64/include/asm/patching.h
>> @@ -8,6 +8,7 @@ int aarch64_insn_read(void *addr, u32 *insnp);
>>   int aarch64_insn_write(void *addr, u32 insn);
>>   
>>   int aarch64_insn_write_literal_u64(void *addr, u64 val);
>> +void *aarch64_insn_copy(void *dst, const void *src, size_t len);
>>   
>>   int aarch64_insn_patch_text_nosync(void *addr, u32 insn);
>>   int aarch64_insn_patch_text(void *addrs[], u32 insns[], int cnt);
>> diff --git a/arch/arm64/kernel/patching.c b/arch/arm64/kernel/patching.c
>> index b4835f6d594b..243d6ae8d2d8 100644
>> --- a/arch/arm64/kernel/patching.c
>> +++ b/arch/arm64/kernel/patching.c
>> @@ -105,6 +105,47 @@ noinstr int aarch64_insn_write_literal_u64(void *addr, u64 val)
>>   	return ret;
>>   }
>>   
>> +/**
>> + * aarch64_insn_copy - Copy instructions into (an unused part of) RX memory
>> + * @dst: address to modify
>> + * @src: source of the copy
>> + * @len: length to copy
>> + *
>> + * Useful for JITs to dump new code blocks into unused regions of RX memory.
>> + */
>> +noinstr void *aarch64_insn_copy(void *dst, const void *src, size_t len)
>> +{
>> +	unsigned long flags;
>> +	size_t patched = 0;
>> +	size_t size;
>> +	void *waddr;
>> +	void *ptr;
>> +	int ret;
>> +
>
> check whether the input address and length are aligned to instruction size?

Will add a check that dst is aligned to instruction size and len is a
multiple of instruction size.

>
>> +	raw_spin_lock_irqsave(&patch_lock, flags);
>> +
>> +	while (patched < len) {
>> +		ptr = dst + patched;
>> +		size = min_t(size_t, PAGE_SIZE - offset_in_page(ptr),
>> +			     len - patched);
>> +
>> +		waddr = patch_map(ptr, FIX_TEXT_POKE0);
>> +		ret = copy_to_kernel_nofault(waddr, src + patched, size);
>> +		patch_unmap(FIX_TEXT_POKE0);
>> +
>> +		if (ret < 0) {
>> +			raw_spin_unlock_irqrestore(&patch_lock, flags);
>> +			return NULL;
>> +		}
>> +		patched += size;
>> +	}
>> +	raw_spin_unlock_irqrestore(&patch_lock, flags);
>> +
>> +	caches_clean_inval_pou((uintptr_t)dst, (uintptr_t)dst + len);
>> +
>
> seems flush_icache_range() or something like should be called here to
> ensure the other CPUs' pipelines are cleared, otherwise the old instructions
> at the dst address might be executed on other CPUs after the copy is complete,
> which is not expected.

Sure, I will use flush_icache_range() in place of
caches_clean_inval_pou() in the next version 

>
>> +	return dst;
>> +}
>> +
>>   int __kprobes aarch64_insn_patch_text_nosync(void *addr, u32 insn)
>>   {
>>   	u32 *tp = addr;