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Date:   Tue, 22 Nov 2022 20:13:43 +0700
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To:     Jens Axboe <axboe@kernel.dk>
Cc:     Stefan Roesch <shr@devkernel.io>,
        Facebook Kernel Team <kernel-team@fb.com>,
        Olivier Langlois <olivier@trillion01.com>,
        netdev Mailing List <netdev@vger.kernel.org>,
        io-uring Mailing List <io-uring@vger.kernel.org>,
        Jakub Kicinski <kuba@kernel.org>
References: <20221121191437.996297-1-shr@devkernel.io>
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 <35168b29-a81c-e1b2-7ec9-b5f0b896ee74@kernel.dk>
From:   Ammar Faizi <ammarfaizi2@gnuweeb.org>
Subject: Re: [PATCH v5 2/3] io_uring: add api to set / get napi configuration.
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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.

-- 
Ammar Faizi