xen-devel.lists.xenproject.org archive mirror
 help / color / mirror / Atom feed
From: Christoph Hellwig <hch@lst.de>
To: Stefano Stabellini <sstabellini@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>, Julien Grall <julien@xen.org>,
	f.fainelli@gmail.com,
	"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
	linux-kernel@vger.kernel.org,
	osstest service owner <osstest-admin@xenproject.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	iommu@lists.linux-foundation.org
Subject: Re: Regression when booting 5.15 as dom0 on arm64 (WAS: Re: [linux-linus test] 161829: regressions - FAIL)
Date: Tue, 11 May 2021 08:35:58 +0200	[thread overview]
Message-ID: <20210511063558.GA7605@lst.de> (raw)
In-Reply-To: <alpine.DEB.2.21.2105101818260.5018@sstabellini-ThinkPad-T480s>

On Mon, May 10, 2021 at 06:46:34PM -0700, Stefano Stabellini wrote:
> On Mon, 10 May 2021, Christoph Hellwig wrote:
> > On Sat, May 08, 2021 at 12:32:37AM +0100, Julien Grall wrote:
> > > The pointer dereferenced seems to suggest that the swiotlb hasn't been 
> > > allocated. From what I can tell, this may be because swiotlb_force is set 
> > > to SWIOTLB_NO_FORCE, we will still enable the swiotlb when running on top 
> > > of Xen.
> > >
> > > I am not entirely sure what would be the correct fix. Any opinions?
> > 
> > Can you try something like the patch below (not even compile tested, but
> > the intent should be obvious?
> > 
> > 
> > diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> > index 16a2b2b1c54d..7671bc153fb1 100644
> > --- a/arch/arm64/mm/init.c
> > +++ b/arch/arm64/mm/init.c
> > @@ -44,6 +44,8 @@
> >  #include <asm/tlb.h>
> >  #include <asm/alternative.h>
> >  
> > +#include <xen/arm/swiotlb-xen.h>
> > +
> >  /*
> >   * We need to be able to catch inadvertent references to memstart_addr
> >   * that occur (potentially in generic code) before arm64_memblock_init()
> > @@ -482,7 +484,7 @@ void __init mem_init(void)
> >  	if (swiotlb_force == SWIOTLB_FORCE ||
> >  	    max_pfn > PFN_DOWN(arm64_dma_phys_limit))
> >  		swiotlb_init(1);
> > -	else
> > +	else if (!IS_ENABLED(CONFIG_XEN) || !xen_swiotlb_detect())
> >  		swiotlb_force = SWIOTLB_NO_FORCE;
> >  
> >  	set_max_mapnr(max_pfn - PHYS_PFN_OFFSET);
> 
> The "IS_ENABLED(CONFIG_XEN)" is not needed as the check is already part
> of xen_swiotlb_detect().

As far as I can tell the x86 version of xen_swiotlb_detect has a
!CONFIG_XEN stub.  The arm/arm64 version in uncoditionally declared, but
the implementation only compiled when Xen support is enabled.

> 
> 
> But let me ask another question first. Do you think it makes sense to have:
> 
> 	if (swiotlb_force == SWIOTLB_NO_FORCE)
> 		return 0;
> 
> at the beginning of swiotlb_late_init_with_tbl? I am asking because
> swiotlb_late_init_with_tbl is meant for special late initializations,
> right? It shouldn't really matter the presence or absence of
> SWIOTLB_NO_FORCE in regards to swiotlb_late_init_with_tbl. Also the
> commit message for "swiotlb: Make SWIOTLB_NO_FORCE perform no
> allocation" says that "If a platform was somehow setting
> swiotlb_no_force and a later call to swiotlb_init() was to be made we
> would still be proceeding with allocating the default SWIOTLB size
> (64MB)." Our case here is very similar, right? So the allocation should
> proceed?

Well, right now SWIOTLB_NO_FORCE is checked in dma_direct_map_page.
We need to clean all this up a bit, especially with the work to support
multiple swiotlb buffers, but I think for now this is the best we can
do.

> Which brings me to a separate unrelated issue, still affecting the path
> xen_swiotlb_init -> swiotlb_late_init_with_tbl. If swiotlb_init(1) is
> called by mem_init then swiotlb_late_init_with_tbl will fail due to the
> check:
> 
>     /* protect against double initialization */
>     if (WARN_ON_ONCE(io_tlb_default_mem))
>         return -ENOMEM;
> 
> xen_swiotlb_init is meant to ask Xen to make a bunch of pages physically
> contiguous. Then, it initializes the swiotlb buffer based on those
> pages. So it is a problem that swiotlb_late_init_with_tbl refuses to
> continue. However, in practice it is not a problem today because on ARM
> we don't actually make any special requests to Xen to make the pages
> physically contiguous (yet). See the empty implementation of
> arch/arm/xen/mm.c:xen_create_contiguous_region. I don't know about x86.
> 
> So maybe we should instead do something like the appended?

So I'd like to change the core swiotlb initialization to just use
a callback into the arch/xen code to make the pages contigous and
kill all that code duplication.  Together with the multiple swiotlb
buffer work I'd rather avoid churn that goes into a different direction
if possible.


  reply	other threads:[~2021-05-11  6:36 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-07 21:00 [linux-linus test] 161829: regressions - FAIL osstest service owner
2021-05-07 23:32 ` Regression when booting 5.15 as dom0 on arm64 (WAS: Re: [linux-linus test] 161829: regressions - FAIL) Julien Grall
2021-05-10  8:40   ` Christoph Hellwig
2021-05-10 18:15     ` Julien Grall
2021-05-10 19:04       ` Florian Fainelli
2021-05-11  1:46     ` Stefano Stabellini
2021-05-11  6:35       ` Christoph Hellwig [this message]
2021-05-11 16:47         ` Regression when booting 5.15 as dom0 on arm64 (WAS: Re: [linux-linus test] 161829: regressions - FAIL)] Stefano Stabellini
2021-05-11 16:49           ` Christoph Hellwig
2021-05-11 16:51             ` Stefano Stabellini
2021-05-11 17:01               ` Christoph Hellwig

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20210511063558.GA7605@lst.de \
    --to=hch@lst.de \
    --cc=boris.ostrovsky@oracle.com \
    --cc=f.fainelli@gmail.com \
    --cc=iommu@lists.linux-foundation.org \
    --cc=julien@xen.org \
    --cc=konrad.wilk@oracle.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=osstest-admin@xenproject.org \
    --cc=sstabellini@kernel.org \
    --cc=xen-devel@lists.xenproject.org \
    --subject='Re: Regression when booting 5.15 as dom0 on arm64 (WAS: Re: [linux-linus test] 161829: regressions - FAIL)' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).