netdev - Re: [RFC PATCH v4 2/3] io_uring: add api to set / get napi configuration.

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Date:   Mon, 21 Nov 2022 10:56:39 -0800
From:   Stefan Roesch <shr@...kernel.io>
To:     Ammar Faizi <ammarfaizi2@...weeb.org>
Cc:     Facebook Kernel Team <kernel-team@...com>,
        Jens Axboe <axboe@...nel.dk>,
        Olivier Langlois <olivier@...llion01.com>,
        netdev Mailing List <netdev@...r.kernel.org>,
        io-uring Mailing List <io-uring@...r.kernel.org>,
        Jakub Kicinski <kuba@...nel.org>
Subject: Re: [RFC PATCH v4 2/3] io_uring: add api to set / get napi
 configuration.


Ammar Faizi <ammarfaizi2@...weeb.org> writes:

> On 11/22/22 12:29 AM, Stefan Roesch wrote:
>> +static int io_register_napi(struct io_ring_ctx *ctx, void __user *arg)
>> +{
>> +#ifdef CONFIG_NET_RX_BUSY_POLL
>> +	const struct io_uring_napi curr = {
>> +		.busy_poll_to = ctx->napi_busy_poll_to,
>> +	};
>> +	struct io_uring_napi *napi;
>> +
>> +	napi = memdup_user(arg, sizeof(*napi));
>> +	if (IS_ERR(napi))
>> +		return PTR_ERR(napi);
>> +
>> +	WRITE_ONCE(ctx->napi_busy_poll_to, napi->busy_poll_to);
>> +
>> +	kfree(napi);
>> +
>> +	if (copy_to_user(arg, &curr, sizeof(curr)))
>> +		return -EFAULT;
>> +
>> +	return 0;
>
> Considering:
>
>    1) `struct io_uring_napi` is 16 bytes in size.
>
>    2) The lifetime of `struct io_uring_napi *napi;` is brief.
>
> There is no need to use memdup_user() and kfree(). You can place it
> on the stack and use copy_from_user() instead.

The next version of the patch will use copy_from_user.