linux-kernel - Re: ehci-pci breakage with dma-mapping changes in 5.4-rc2

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Date:   Mon, 7 Oct 2019 19:54:02 -0400
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Arvind Sankar <nivedita@...m.mit.edu>
Cc:     Christoph Hellwig <hch@....de>,
        Christoph Hellwig <hch@...radead.org>,
        linux-kernel@...r.kernel.org
Subject: Re: ehci-pci breakage with dma-mapping changes in 5.4-rc2

On Mon, Oct 07, 2019 at 06:10:55PM -0400, Arvind Sankar wrote:
> On Mon, Oct 07, 2019 at 08:47:54PM +0200, Christoph Hellwig wrote:
> > On Mon, Oct 07, 2019 at 02:32:07PM -0400, Arvind Sankar wrote:
> > > On Mon, Oct 07, 2019 at 01:58:57PM -0400, Arvind Sankar wrote:
> > > > On Mon, Oct 07, 2019 at 10:56:30AM -0700, Christoph Hellwig wrote:
> > > > > On Mon, Oct 07, 2019 at 07:55:28PM +0200, Christoph Hellwig wrote:
> > > > > > On Mon, Oct 07, 2019 at 01:54:32PM -0400, Arvind Sankar wrote:
> > > > > > > It doesn't boot with the patch. Won't it go
> > > > > > > 	dma_get_required_mask
> > > > > > > 	-> intel_get_required_mask
> > > > > > > 	-> iommu_need_mapping
> > > > > > > 	-> dma_get_required_mask
> > > > > > > ?
> > > > > > > 
> > > > > > > Should the call to dma_get_required_mask in iommu_need_mapping be
> > > > > > > replaced with dma_direct_get_required_mask on top of your patch?
> > > > > > 
> > > > > > Yes, sorry.
> > > > > 
> > > > > Actually my patch already calls dma_direct_get_required_mask.
> > > > > How did you get the loop?
> > > > 
> > > > The function iommu_need_mapping (not changed by your patch) calls
> > > > dma_get_required_mask internally, to check whether the device's dma_mask
> > > > is big enough or not. That's the call I was asking whether it needs to
> > > > be changed.
> > > 
> > > Yeah the attached patch seems to fix it.
> > 
> > That looks fine to me:
> > 
> > Acked-by: Christoph Hellwig <hch@....de>
> 
> Do you want me to resend the patch as its own mail, or do you just take
> it with a Tested-by: from me? If the former, I assume you're ok with me
> adding your Signed-off-by?
> 
> Thanks

A question on the original change though -- what happens if a single
device (or a single IOMMU domain really) does want >4G DMA address
space? Was that not previously allowed either?