On Wed, Feb 25, 2026 at 11:20:10PM +0000, David Matlack wrote: > On 2026-02-25 04:47 PM, Bjorn Helgaas wrote: > > On Thu, Jan 29, 2026 at 09:24:50PM +0000, David Matlack wrote: > > > Inherit bus numbers from the previous kernel during a Live Update when > > > one or more PCI devices are being preserved. This is necessary so that > > > preserved devices can DMA through the IOMMU during a Live Update > > > (changing bus numbers would break IOMMU translation). > > > > I think changing bus numbers would break DMA regardless of whether an > > IOMMU is involved. Completions carrying the data for DMA reads are > > routed back to the Requester ID of the read. > > Ahh, makes sense. I'll clarify the commit message in the next > version.
More broadly you can't shouldn't the fabric topology while Memory Enable is active. Renumbering or readdressing the fabric requires disabling and flushing any memory transactions. >From that reasoning it is clearer that you can't do that if the device is expected to hitlesslly continue performing memory operations. That may be a clearer long term basis for describing the requirements here. Jason
