From: Kalle Valo <kvalo@codeaurora.org>
To: Christian Lamparter <chunkeey@gmail.com>
Cc: Jia-Ju Bai <baijiaju@tsinghua.edu.cn>,
kuba@kernel.org, linux-wireless@vger.kernel.org
Subject: Re: [PATCH] p54: avoid accessing the data mapped to streaming DMA
Date: Wed, 26 Aug 2020 19:02:43 +0300 [thread overview]
Message-ID: <873649cs4c.fsf@codeaurora.org> (raw)
In-Reply-To: <0b432282-8d52-3004-6648-d97c03cdae28@gmail.com> (Christian Lamparter's message of "Tue, 18 Aug 2020 19:27:10 +0200")
Christian Lamparter <chunkeey@gmail.com> writes:
> On 2020-08-02 15:29, Jia-Ju Bai wrote:
>> In p54p_tx(), skb->data is mapped to streaming DMA on line 337:
>> mapping = pci_map_single(..., skb->data, ...);
>>
>> Then skb->data is accessed on line 349:
>> desc->device_addr = ((struct p54_hdr *)skb->data)->req_id;
>>
>> This access may cause data inconsistency between CPU cache and hardware.
>>
>> To fix this problem, ((struct p54_hdr *)skb->data)->req_id is stored in
>> a local variable before DMA mapping, and then the driver accesses this
>> local variable instead of skb->data.
>
> Interesting. Please bear with me here. From my understanding, the
> streaming direction is set to PCI_DMA_TODEVICE. So is it really
> possible for the hardware to interfere with the data without the IOMMU
> catching this?
Also is there any documentation about this scenario? I would like to
understand this better.
> (That said, patch looks be fine. I'll need to dust off a old PCI PC to
> check this with real hardware, if requested.)
No need to test with real hardware for my sake, but a careful review is
very much appreciated.
--
https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches
next prev parent reply other threads:[~2020-08-26 16:03 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-02 13:29 [PATCH] p54: avoid accessing the data mapped to streaming DMA Jia-Ju Bai
2020-08-18 12:41 ` Kalle Valo
2020-08-18 17:27 ` Christian Lamparter
2020-08-26 16:02 ` Kalle Valo [this message]
2020-08-28 21:19 ` Christian Lamparter
2020-08-31 14:00 ` Kalle Valo
2020-09-01 9:34 ` Kalle Valo
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