On Tue, Mar 11, 2025 at 4:02 AM Suthikulpanit, Suravee < [email protected]> wrote:
> > > On 3/9/2025 8:44 PM, Michael S. Tsirkin wrote: > > On Tue, Mar 04, 2025 at 06:37:47PM +0000, Suravee Suthikulpanit wrote: > >> The QEMU-emulated AMD IOMMU PCI device is implemented based on the AMD > I/O > >> Virtualization Technology (IOMMU) Specification [1]. The PCI id for this > >> device is platform-specific. > >> > >> Currently, the QEMU-emulated AMD IOMMU device is using AMD vendor id and > >> undefined device id. > >> > >> Therefore, change the vendor id to Red Hat and request a new > QEMU-specific > >> device id. > >> > >> [1] > https://www.amd.com/content/dam/amd/en/documents/processor-tech-docs/specifications/48882_IOMMU.pdf > >> > >> Cc: Gerd Hoffmann <[email protected]> > >> Signed-off-by: Suravee Suthikulpanit <[email protected]> > > > > Will the existing drivers bind with the device then? > > Existing Windows would not recognize the device ID. > > Actually, Linux and Windows does not depend on the PCI vendor / device > ids to probe devices and initialize AMD IOMMU. Instead, it depends on > the ACPI IVRS table. > > Checking on a real system w/ AMD IOMMU enabled booting Windows Server > 2022, there is no AMD IOMMU device showing in the Device Manger. > > In this case, I believe Windows is not fully initializing the > QEMU-emulated AMD IOMMU. So Windows would not remove the IOMMU PCIe from > the list of OS visible devices and therefore expose the PNPID to the > device manager. And since the device ID is zero, it appears as an "Other > devices->PCI Device (with warning sign). > > Therefore, it we have two options: > > 1. Fake the device ID to 0x1419, which is current appear in the > machine.inf as an entry in section [AMD_SYS.NTamd64]: > > %IommuDevice_Desc% = NO_DRV,PCI\VEN_1022&DEV_1419 > Considering that this is a "null driver" (no actual driver is loaded for the PCIe endpoint according to machine.inf), I recommend using this PNP ID. > > 2. Figure out why Windows does not recognize the device. > The answer is simple: the PCIe endpoint's PNP ID is unknown to Windows. So technically device is recognized (it is shown in Device Manager after all), but there are no compatible drivers for it. And in anycase, machine.inf specifies "null driver" for AMD PCIe endpoint IOMMU device. The device will get a friendly name in Device Manager and considered to be "installed" by Windows, by there is no actual driver associated with the device. Best regards, Yan. > > Anyhow, we should still assign some PCI ID value (instead of zero). > > Thanks, > Suravee > > > >
