linux-kernel - Re: [PATCH 01/10] swiotlb-xen: use vmalloc_to

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Date:   Fri, 22 May 2020 13:36:20 -0700 (PDT)
From:   Stefano Stabellini <sstabellini@...nel.org>
To:     Julien Grall <julien@....org>
cc:     Stefano Stabellini <sstabellini@...nel.org>, jgross@...e.com,
        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        Stefano Stabellini <stefano.stabellini@...inx.com>
Subject: Re: [PATCH 01/10] swiotlb-xen: use vmalloc_to_page on vmalloc virt
 addresses

On Fri, 22 May 2020, Julien Grall wrote:
> Hi Stefano,
> 
> On 22/05/2020 04:54, Stefano Stabellini wrote:
> > On Thu, 21 May 2020, Julien Grall wrote:
> > > Hi,
> > > 
> > > On 21/05/2020 00:45, Stefano Stabellini wrote:
> > > > From: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> > > > 
> > > > Don't just assume that virt_to_page works on all virtual addresses.
> > > > Instead add a is_vmalloc_addr check and use vmalloc_to_page on vmalloc
> > > > virt addresses.
> > > 
> > > Can you provide an example where swiotlb is used with vmalloc()?
> > 
> > The issue was reported here happening on the Rasperry Pi 4:
> > https://marc.info/?l=xen-devel&m=158862573216800
> 
> Thanks, it would be good if the commit message contains a bit more details.
> 
> > 
> > If you are asking where in the Linux codebase the vmalloc is happening
> > specifically, I don't know for sure, my information is limited to the
> > stack trace that you see in the link (I don't have a Rasperry Pi 4 yet
> > but I shall have one soon.)
> 
> Looking at the code there is a comment in xen_swiotlb_alloc_coherent()
> suggesting that xen_alloc_coherent_pages() may return an ioremap'ped region on
> Arm. So it feels to me that commit b877ac9815a8fe7e5f6d7fdde3dc34652408840a
> "xen/swiotlb: remember having called xen_create_contiguous_region()" has
> always been broken on Arm.

Yes, I think you are right


> As an aside, your commit message also suggests this is an issue for every
> virtual address used in swiotlb. But only the virt_to_page() call in
> xen_swiotlb_free_coherent() is modified. Is it intended? If yes, I think you
> want to update your commit message.

I see, yes I can explain better