From: Vasant Hegde <vasant.hegde@amd.com>
To: Christos Longros <chris.longros@gmail.com>,
Joerg Roedel <joro@8bytes.org>
Cc: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
Will Deacon <will@kernel.org>,
Robin Murphy <robin.murphy@arm.com>,
Jonathan Corbet <corbet@lwn.net>,
Shuah Khan <skhan@linuxfoundation.org>,
iommu@lists.linux.dev, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] iommu/amd: add amd_iommu=relax_unity option for VFIO passthrough
Date: Mon, 30 Mar 2026 15:32:06 +0530 [thread overview]
Message-ID: <294eb576-dcaf-45e2-bee5-558eaedc4a55@amd.com> (raw)
In-Reply-To: <20260328213228.12084-1-chris.longros@gmail.com>
Hi Christos,
On 3/29/2026 3:02 AM, Christos Longros wrote:
> On some AMD motherboards (Gigabyte B650 Gaming X AX V2, X870E and
> others), VFIO passthrough of any PCI device fails with:
>
> "Firmware has requested this device have a 1:1 IOMMU mapping,
> rejecting configuring the device without a 1:1 mapping."
>
> These boards' IVRS tables include IVMD type 0x22 (range) entries
> spanning wide device ranges (e.g. devid 0x0000 to 0x0FFF, covering
> PCI buses 0-15). The entries exist for platform devices like IOAPIC
> and HPET, but they get applied to nearly every IOMMU group on the
> system. Since commit a48ce36e2786 ("iommu: Prevent RESV_DIRECT
> devices from blocking domains"), any device with IOMMU_RESV_DIRECT
> regions has require_direct=1 set, which prevents VFIO from claiming
> DMA ownership.
I don't have client system handy to verify. Do you have acpi dump?
I want to see IVMD flags are set.
>
> No PCI device can be passed through on affected boards -- not just
> the platform devices that need the identity mappings, but also
> endpoint devices like network adapters and GPUs.
>
> Intel handles a similar firmware over-specification with
> device_rmrr_is_relaxable(), which marks certain RMRR entries as
> IOMMU_RESV_DIRECT_RELAXABLE so VFIO can claim them. AMD has no
> equivalent.
May be we can do similar for pci devices instead of command line option?
-Vasant
prev parent reply other threads:[~2026-03-30 10:02 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-28 21:32 [PATCH] iommu/amd: add amd_iommu=relax_unity option for VFIO passthrough Christos Longros
2026-03-30 10:02 ` Vasant Hegde [this message]
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