Re: [PATCH v2 06/19] iommufd/viommu: Add IOMMU_VIOMMU_SET/UNSET_VDEV_ID ioctl
From: Nicolin Chen <hidden>
Date: 2025-05-06 19:55:32
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linux-iommu, linux-kselftest, lkml
On Tue, May 06, 2025 at 09:58:47AM -0300, Jason Gunthorpe wrote:
On Mon, May 05, 2025 at 07:53:44PM -0700, Nicolin Chen wrote:quoted
On Mon, May 05, 2025 at 02:08:07PM -0300, Jason Gunthorpe wrote:quoted
On Wed, Apr 30, 2025 at 12:58:47AM -0700, Nicolin Chen wrote: The bus numbers can be reassigned at any time on the fly by the guest by reprogramming the PCI hierarchy.Yes. If we take some aggressive use case into account, where its BDF number could change multiple times, I think it's natural for VMM to simply destroy the previous vDEVICE and allocate a new one with a new BDF number, right?We should not destroy the vdevice for something like that. In a CC case that would unplug it from the VM which is not right.
CC needs BDF to allocate a VDEV in the CC world. So, it cannot allocate a VDEV with BDF=0 firstly, which is what Alex reported. And even for a normal case that the device is migrating between PCI buses, CC might not be able to update the BDF (which can be a part of CC_VDEV_ALLOC instruction), even if iommufd supports an update ioctl. So, the underlying handler for an update ioctl is still to first destroy the VDEV and re-allocate a new one? Thanks Nicolin