netdev - Re: [PATCH v5 2/3] io_uring: add api to set / get napi configuration.

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Message-ID: <06973f73-16c9-1e21-3416-bc624b8675e4@kernel.dk>
Date:   Tue, 22 Nov 2022 06:19:01 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Ammar Faizi <ammarfaizi2@...weeb.org>
Cc:     Stefan Roesch <shr@...kernel.io>,
        Facebook Kernel Team <kernel-team@...com>,
        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: [PATCH v5 2/3] io_uring: add api to set / get napi configuration.

On 11/22/22 6:13 AM, Ammar Faizi wrote:
> On 11/22/22 2:46 AM, Jens Axboe wrote:
>> On 11/21/22 12:14?PM, Stefan Roesch wrote:
>>> +static int io_unregister_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,
>>> +    };
>>> +
>>> +    if (copy_to_user(arg, &curr, sizeof(curr)))
>>> +        return -EFAULT;
>>> +
>>> +    WRITE_ONCE(ctx->napi_busy_poll_to, 0);
>>> +    return 0;
>>> +#else
>>> +    return -EINVAL;
>>> +#endif
>>> +}
>>
>> Should probably check resv/pad here as well, maybe even the
>> 'busy_poll_to' being zero?
> 
> Jens, this function doesn't read from __user memory, it writes to
> __user memory.
> 
> @curr.resv and @curr.pad are on the kernel's stack. Both are already
> implicitly initialized to zero by the partial struct initializer.

Oh yes, guess I totally missed that we don't care about the value
at all (just zero the target) and copy back the old values.

-- 
Jens Axboe