From: Kai-Heng Feng <kai.heng.feng@canonical.com>
To: Robin Murphy <robin.murphy@arm.com>
Cc: Joerg Roedel <joro@8bytes.org>,
will@kernel.org,
"open list:AMD IOMMU (AMD-VI)" <iommu@lists.linux-foundation.org>,
open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] iommu/amd: Enable swiotlb if any device supports iommu v2 and uses identity mapping
Date: Thu, 8 Jul 2021 21:57:00 +0800 [thread overview]
Message-ID: <CAAd53p40RcG0oeYr9QAKMjYRtyq7he=d_b_a39n4Rt5JSVScRQ@mail.gmail.com> (raw)
In-Reply-To: <fde11cec-d1bd-49be-f129-c69a973d1b3b@arm.com>
On Thu, Jul 8, 2021 at 6:18 PM Robin Murphy <robin.murphy@arm.com> wrote:
>
> On 2021-07-08 10:28, Joerg Roedel wrote:
> > On Thu, Jul 08, 2021 at 03:42:32PM +0800, Kai-Heng Feng wrote:
> >> @@ -344,6 +344,9 @@ static int iommu_init_device(struct device *dev)
> >>
> >> iommu = amd_iommu_rlookup_table[dev_data->devid];
> >> dev_data->iommu_v2 = iommu->is_iommu_v2;
> >> +
> >> + if (dev_data->iommu_v2)
> >> + swiotlb = 1;
> >
> > This looks like the big hammer, as it will affect all other systems
> > where the AMD GPUs are in their own group.
> >
> > What is needed here is an explicit check whether a non-iommu-v2 device
> > is direct-mapped because it shares a group with the GPU, and only enable
> > swiotlb in this case.
>
> Right, it's basically about whether any DMA-limited device might at any
> time end up in an IOMMU_DOMAIN_IDENTITY domain. And given the
> possibility of device hotplug and the user being silly with the sysfs
> interface, I don't think we can categorically determine that at boot time.
>
> Also note that Intel systems are likely to be similarly affected (in
> fact intel-iommu doesn't even have the iommu_default_passthough() check
> so it's probably even easier to blow up).
swiotlb is enabled by pci_swiotlb_detect_4gb() and intel-iommu doesn't
disable it.
I wonder if we can take the same approach in amd-iommu?
Kai-Heng
>
> Robin.
next prev parent reply other threads:[~2021-07-08 13:57 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-08 7:42 [PATCH] iommu/amd: Enable swiotlb if any device supports iommu v2 and uses identity mapping Kai-Heng Feng
2021-07-08 9:28 ` Joerg Roedel
2021-07-08 10:18 ` Robin Murphy
2021-07-08 13:57 ` Kai-Heng Feng [this message]
2021-07-08 14:43 ` Robin Murphy
2021-07-13 23:57 ` Konrad Rzeszutek Wilk
2021-07-14 4:59 ` Kai-Heng Feng
2021-07-14 10:25 ` Joerg Roedel
2021-09-09 6:32 ` Kai-Heng Feng
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