On Wed, Apr 26, 2023 at 02:53:53PM +0100, Robin Murphy wrote: > Give QEMU a way to tell IOMMUFD to associate that 0x08080000 address with a > given device as an MSI target. IOMMUFD then ensures that the S2 mapping > exists from that IPA to the device's real ITS (I vaguely remember Eric had a > patch to pre-populate an MSI cookie with specific pages, which may have been > heading along those lines). This isn't the main problem - already for most cases iommufd makes it so the ITS page is at 0x8000000. We can fix qemu to also use 0x8000000 in the ACPI - it already hardwires this for the RMRR part. We can even make the kernel return the value so it isn't hardwired, easy stuff.. > QEMU will presumably also need a way to pass the VA down to IOMMUFD when it > sees the guest programming the MSI (possibly it could pass the IPA at the > same time so we don't need a distinct step to set up S2 beforehand?) - once > the underlying physical MSI configuration comes back from the PCI layer, > that VA just needs to be dropped in to replace the original msi_msg address. This is the main problem. What ioctl passes the VA, and how does it plumb down into the irq_chip.. This is where everyone gets scared, I think. There is a thick mass of IRQ plumbing and locking between those two points And then it only solves MSI, not the bigger picture.. > TBH at that point it may be easier to just not have a cookie in the S2 > domain at all when nesting is enabled, and just let IOMMUFD make the ITS > mappings directly for itself. Yes, I'd like to get there so replace can work. Jason
