From: Stefano Stabellini <sstabellini@kernel.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
iommu@lists.linux-foundation.org, x86@kernel.org,
Anshuman Khandual <anshuman.khandual@arm.com>,
Tom Lendacky <thomas.lendacky@amd.com>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
Juergen Gross <jgross@suse.com>, Joerg Roedel <joro@8bytes.org>,
David Woodhouse <dwmw2@infradead.org>,
Lu Baolu <baolu.lu@linux.intel.com>,
Robin Murphy <robin.murphy@arm.com>,
linux-arm-kernel@lists.infradead.org,
xen-devel@lists.xenproject.org, linux-ia64@vger.kernel.org,
linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org,
linux-hyperv@vger.kernel.org, tboot-devel@lists.sourceforge.net,
linux-pci@vger.kernel.org
Subject: Re: [PATCH 11/12] swiotlb: merge swiotlb-xen initialization into swiotlb
Date: Fri, 4 Mar 2022 15:22:54 -0800 (PST) [thread overview]
Message-ID: <alpine.DEB.2.22.394.2203041511090.3261@ubuntu-linux-20-04-desktop> (raw)
In-Reply-To: <20220304163430.GA12317@lst.de>
On Fri, 4 Mar 2022, Christoph Hellwig wrote:
> On Thu, Mar 03, 2022 at 02:49:29PM -0800, Stefano Stabellini wrote:
> > On Thu, 3 Mar 2022, Christoph Hellwig wrote:
> > > On Wed, Mar 02, 2022 at 05:25:10PM -0800, Stefano Stabellini wrote:
> > > > Thinking more about it we actually need to drop the xen_initial_domain()
> > > > check otherwise some cases won't be functional (Dom0 not 1:1 mapped, or
> > > > DomU 1:1 mapped).
> > >
> > > Hmm, but that would be the case even before this series, right?
> >
> > Before this series we only have the xen_swiotlb_detect() check in
> > xen_mm_init, we don't have a second xen_initial_domain() check.
> >
> > The issue is that this series is adding one more xen_initial_domain()
> > check in xen_mm_init.
>
> In current mainline xen_mm_init calls xen_swiotlb_init unconditionally.
> But xen_swiotlb_init then calls xen_swiotlb_fixup after allocating
> the memory, which in turn calls xen_create_contiguous_region.
> xen_create_contiguous_region fails with -EINVAL for the
> !xen_initial_domain() and thus caues xen_swiotlb_fixup and
> xen_swiotlb_init to unwind and return -EINVAL.
>
> So as far as I can tell there is no change in behavior, but maybe I'm
> missing something subtle?
You are right.
The xen_initial_domain() check in xen_create_contiguous_region() is
wrong and we should get rid of it. It is a leftover from before the
xen_swiotlb_detect rework.
We could either remove it or change it into another xen_swiotlb_detect()
check.
Feel free to add the patch to your series or fold it with another patch
or rework it as you prefer. Thanks for spotting this!
---
arm/xen: don't check for xen_initial_domain() in xen_create_contiguous_region
It used to be that Linux enabled swiotlb-xen when running a dom0 on ARM.
Since f5079a9a2a31 "xen/arm: introduce XENFEAT_direct_mapped and
XENFEAT_not_direct_mapped", Linux detects whether to enable or disable
swiotlb-xen based on the new feature flags: XENFEAT_direct_mapped and
XENFEAT_not_direct_mapped.
However, there is still a leftover xen_initial_domain() check in
xen_create_contiguous_region. Remove the check as
xen_create_contiguous_region is only called by swiotlb-xen during
initialization. If xen_create_contiguous_region is called, we know Linux
is running 1:1 mapped so there is no need for additional checks.
Also update the in-code comment.
Signed-off-by: Stefano Stabellini <stefano.stabellini@xilinx.com>
diff --git a/arch/arm/xen/mm.c b/arch/arm/xen/mm.c
index a7e54a087b80..28c207060253 100644
--- a/arch/arm/xen/mm.c
+++ b/arch/arm/xen/mm.c
@@ -122,10 +122,7 @@ int xen_create_contiguous_region(phys_addr_t pstart, unsigned int order,
unsigned int address_bits,
dma_addr_t *dma_handle)
{
- if (!xen_initial_domain())
- return -EINVAL;
-
- /* we assume that dom0 is mapped 1:1 for now */
+ /* the domain is 1:1 mapped to use swiotlb-xen */
*dma_handle = pstart;
return 0;
}
next prev parent reply other threads:[~2022-03-04 23:23 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-01 10:52 cleanup swiotlb initialization v4 Christoph Hellwig
2022-03-01 10:53 ` [PATCH 01/12] dma-direct: use is_swiotlb_active in dma_direct_map_page Christoph Hellwig
2022-03-01 10:53 ` [PATCH 02/12] swiotlb: make swiotlb_exit a no-op if SWIOTLB_FORCE is set Christoph Hellwig
2022-03-01 10:53 ` [PATCH 03/12] swiotlb: simplify swiotlb_max_segment Christoph Hellwig
2022-03-01 10:53 ` [PATCH 04/12] swiotlb: rename swiotlb_late_init_with_default_size Christoph Hellwig
2022-03-01 10:53 ` [PATCH 05/12] swiotlb: pass a gfp_mask argument to swiotlb_init_late Christoph Hellwig
2022-03-01 10:53 ` [PATCH 06/12] MIPS/octeon: use swiotlb_init instead of open coding it Christoph Hellwig
2022-03-03 16:39 ` Thomas Bogendoerfer
2022-03-01 10:53 ` [PATCH 07/12] x86: remove the IOMMU table infrastructure Christoph Hellwig
2022-03-01 10:53 ` [PATCH 08/12] x86: centralize setting SWIOTLB_FORCE when guest memory encryption is enabled Christoph Hellwig
2022-03-01 11:39 ` Andrew Cooper
2022-03-01 11:43 ` Christoph Hellwig
2022-03-01 10:53 ` [PATCH 09/12] swiotlb: make the swiotlb_init interface more useful Christoph Hellwig
2022-03-01 10:53 ` [PATCH 10/12] swiotlb: add a SWIOTLB_ANY flag to lift the low memory restriction Christoph Hellwig
2022-03-04 18:12 ` Michael Kelley (LINUX)
2022-03-04 18:27 ` Dongli Zhang
2022-03-06 17:01 ` Michael Kelley (LINUX)
2022-03-01 10:53 ` [PATCH 11/12] swiotlb: merge swiotlb-xen initialization into swiotlb Christoph Hellwig
2022-03-02 2:55 ` Stefano Stabellini
2022-03-02 8:15 ` Christoph Hellwig
2022-03-03 1:25 ` Stefano Stabellini
2022-03-03 10:59 ` Christoph Hellwig
2022-03-03 22:49 ` Stefano Stabellini
2022-03-04 16:34 ` Christoph Hellwig
2022-03-04 23:22 ` Stefano Stabellini [this message]
2022-03-02 13:15 ` Boris Ostrovsky
2022-03-02 13:17 ` Boris Ostrovsky
2022-03-03 10:57 ` Christoph Hellwig
2022-03-03 19:06 ` Boris Ostrovsky
2022-03-04 17:28 ` Christoph Hellwig
2022-03-04 17:36 ` Boris Ostrovsky
2022-03-04 17:43 ` Christoph Hellwig
2022-03-04 20:18 ` Boris Ostrovsky
2022-03-04 21:03 ` Christoph Hellwig
2022-03-08 21:38 ` Boris Ostrovsky
2022-03-09 6:18 ` Christoph Hellwig
2022-03-09 15:18 ` Boris Ostrovsky
2022-03-01 10:53 ` [PATCH 12/12] x86: remove cruft from <asm/dma-mapping.h> Christoph Hellwig
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