From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-186.mta0.migadu.com (out-186.mta0.migadu.com [91.218.175.186]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 264661A0BE0 for ; Mon, 30 Jun 2025 21:27:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.186 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1751318874; cv=none; b=FZSLlUMb2h592eDrXPg6BcPpfYCqbqJ+Dhp1rpRSLgLscdfM6/ah8XivyDXx/cxkTjZuOPDjIfZ/ZXbIeja9UnhsDbPhij0IYQmIi9+vALIYZ3iMPKS3HjEgAAHYIsPA/veN042vvEhfK6RSeWAVv4vvOv3WylbUI1OIpCGHOr4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1751318874; c=relaxed/simple; bh=RIghVpgCkOYV78GsfyPYkya5kB0Fm8fmB6QKP1AoKJc=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=Xf088PksX/oEcyRdTu5HYqdT8/M8Xqx2qaYWAvwbYzRmJTjC0uYeNiOLE98+Je3X0UOa72b4q5RJ234mNpt+spmczZBPZEJSlRFd4ZRZD2ykC6EfSIDAkKtXg3KMdRm8HrKXzm5OuJ5Rxm91/0ahs8QexsZ4Kd7djQlD60pNc0w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=GSBaonnE; arc=none smtp.client-ip=91.218.175.186 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="GSBaonnE" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1751318869; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=wWXca6wavz67rxax53JsR8sOjq2No6y5iqrM6wbigGU=; b=GSBaonnE6Q2HzCb+GCdM2NMeZcWWJYTk/rGvvMbG5uUDw+sARFD1+DQDzsMP1c9nq0nKl4 QeGTJSb561DgKFpP4ZgSoNQ57sSTesuEjjE7YoA8VnG+LxiEFIHo25wrNBzMHkBJWdW/zA y/UuqeGMfERRiAIApUcIZCrnEO0AAQc= Date: Mon, 30 Jun 2025 14:27:44 -0700 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH bpf-next v2 1/2] bpf: add bpf_dynptr_memset() kfunc X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Ihor Solodrai To: Mykyta Yatsenko , bpf@vger.kernel.org Cc: andrii@kernel.org, ast@kernel.org, eddyz87@gmail.com, mykolal@fb.com, kernel-team@meta.com References: <20250624205240.1311453-1-isolodrai@meta.com> <20250624205240.1311453-2-isolodrai@meta.com> <36486564-3ce7-403b-91e4-268cae1c4905@gmail.com> <32a3de5b-381a-47a0-910e-ea8b02c4cf90@linux.dev> Content-Language: en-US In-Reply-To: <32a3de5b-381a-47a0-910e-ea8b02c4cf90@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 6/30/25 2:05 PM, Ihor Solodrai wrote: > On 6/25/25 4:27 AM, Mykyta Yatsenko wrote: >> On 6/24/25 21:52, Ihor Solodrai wrote: >>> Currently there is no straightforward way to fill dynptr memory with a >>> value (most commonly zero). One can do it with bpf_dynptr_write(), but >>> a temporary buffer is necessary for that. >>> >>> Implement bpf_dynptr_memset() - an analogue of memset() from libc. >>> >>> Signed-off-by: Ihor Solodrai >>> --- >>>   kernel/bpf/helpers.c | 48 ++++++++++++++++++++++++++++++++++++++++++++ >>>   1 file changed, 48 insertions(+) >>> >>> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c >>> index b71e428ad936..b8a7dbc971b4 100644 >>> --- a/kernel/bpf/helpers.c >>> +++ b/kernel/bpf/helpers.c >>> @@ -2906,6 +2906,53 @@ __bpf_kfunc int bpf_dynptr_copy(struct >>> bpf_dynptr *dst_ptr, u32 dst_off, >>>       return 0; >>>   } >>> +/** >>> + * bpf_dynptr_memset() - Fill dynptr memory with a constant byte. >>> + * @ptr: Destination dynptr - where data will be filled >>> + * @ptr_off: Offset into the dynptr to start filling from >>> + * @size: Number of bytes to fill >>> + * @val: Constant byte to fill the memory with >>> + * >>> + * Fills the size bytes of the memory area pointed to by ptr >>> + * at offset ptr_off with the constant byte val. >>> + * Returns 0 on success; negative error, otherwise. >>> + */ >>> + __bpf_kfunc int bpf_dynptr_memset(struct bpf_dynptr *ptr, u32 >>> ptr_off, u32 size, u8 val) >>> + { >>> +    struct bpf_dynptr_kern *p = (struct bpf_dynptr_kern *)ptr; >>> +    char buf[256]; >>> +    u32 chunk_sz; >>> +    void* slice; >>> +    u32 offset; >>> +    int err; >>> + >>> +    if (__bpf_dynptr_is_rdonly(p)) >>> +        return -EINVAL; >>> + >>> +    err = bpf_dynptr_check_off_len(p, ptr_off, size); >>> +    if (err) >>> +        return err; >>> + >>> +    slice = bpf_dynptr_slice_rdwr(ptr, ptr_off, NULL, size); >>> +    if (likely(slice)) { >>> +        memset(slice, val, size); >>> +        return 0; >>> +    } >> >> bpf_dynptr_slice_rdwr is doing rdonly and off_len checks anyways, so >> perhaps we can >> avoid calling __bpf_dynptr_is_rdonly and bpf_dynptr_check_off_len >> before bpf_dynptr_slice_rdwr, >> that'll make fast path a little faster. > > Yes, there are quite a bit of repetitive checks. > Same in bpf_dynptr_write() in the slow path. > > In case of bpf_dynptr_slice_rdwr() the issue is that it returns a > pointer, and if we only check for null pointer we lose the information > about the error cause (is it readonly or size?). So I think it's > better to leave explicit checks. I just realized that I might have misunderstood your comment. Did you mean to put the checks after bpf_dynptr_slice_rdwr() call instead of before? > >> >>> + >>> +    /* Non-linear data under the dynptr, write from a local buffer */ >>> +    chunk_sz = min_t(u32, sizeof(buf), size); >>> +    memset(buf, val, chunk_sz); >>> + >>> +    for (offset = ptr_off; offset < ptr_off + size; offset += >>> chunk_sz) { >>> +        chunk_sz = min_t(u32, sizeof(buf), size - offset); >>> +        err = __bpf_dynptr_write(p, offset, buf, chunk_sz, 0); >>> +        if (err) >>> +            return err; >>> +    } >>> + >>> +    return 0; >>> +} >>> + >>>   __bpf_kfunc void *bpf_cast_to_kern_ctx(void *obj) >>>   { >>>       return obj; >>> @@ -3364,6 +3411,7 @@ BTF_ID_FLAGS(func, bpf_dynptr_is_rdonly) >>>   BTF_ID_FLAGS(func, bpf_dynptr_size) >>>   BTF_ID_FLAGS(func, bpf_dynptr_clone) >>>   BTF_ID_FLAGS(func, bpf_dynptr_copy) >>> +BTF_ID_FLAGS(func, bpf_dynptr_memset) >>>   #ifdef CONFIG_NET >>>   BTF_ID_FLAGS(func, bpf_modify_return_test_tp) >>>   #endif >> >