linux-kernel - Re: iwlwifi: Regression after migrating to 6.6.32

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Date: Thu, 13 Jun 2024 09:40:26 +0200
From: Johannes Berg <johannes@...solutions.net>
To: Baochen Qiang <quic_bqiang@...cinc.com>, Fabio Estevam
 <festevam@...il.com>
Cc: miriam.rachel.korenblit@...el.com, kvalo@...nel.org, Jakub Kicinski
	 <kuba@...nel.org>, linux-wireless <linux-wireless@...r.kernel.org>, 
 linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: iwlwifi: Regression after migrating to 6.6.32

On Thu, 2024-06-13 at 15:10 +0800, Baochen Qiang wrote:
> 
> On 6/13/2024 3:15 AM, Fabio Estevam wrote:
> > Hi Johannes,
> > 
> > On Wed, Jun 12, 2024 at 4:10 PM Johannes Berg <johannes@...solutions.net> wrote:
> > 
> > > Strange. Is there an IOMMU involved on this platform?
> > 
> > IOMMU isn't available on i.MX8M as far as I know.
> If IOMMU not present, likely the buffer is mapped by SWIOTLB.

Why? The device can do 64-bit DMA, so should be able to just access any
page in the system. Even older devices can do 36-bit DMA, but this is a
newer one. And if IOMMU isn't present, you have no protection anyway.

>  The iova 4215433216, aka 0xFB426800, is 2K aligned, which also supports such guessing. See definition of IO_TLB_SIZE.

Not sure that means anything though, I really would have expected a 4k
buffer to be 4k aligned - why would you even want to map it across two
pages?

If it is SWIOTLB, shouldn't we get into this condition?

        /*
         * Historically, swiotlb allocations >= PAGE_SIZE were guaranteed to be
         * page-aligned in the absence of any other alignment requirements.
         * 'alloc_align_mask' was later introduced to specify the alignment
         * explicitly, however this is passed as zero for streaming mappings
         * and so we preserve the old behaviour there in case any drivers are
         * relying on it.
         */
        if (!alloc_align_mask && !iotlb_align_mask && alloc_size >= PAGE_SIZE)
                alloc_align_mask = PAGE_SIZE - 1;


Otherwise, not sure though how we could possibly fix this in the driver,
we really shouldn't do dma_set_min_align_mask() since on the TX side we
really have no alignment requirements, and swiotlb_map() uses 0 as
alignment.

johannes