On Wed, Mar 04, 2020 at 02:37:08PM +0100, Joerg Roedel wrote: > Hi Michael, > > On Tue, Mar 03, 2020 at 11:09:41AM -0500, Michael S. Tsirkin wrote: > > No. It's coded into the hardware. Which might even be practical > > for bare-metal (e.g. on-board flash), but is very practical > > when the device is part of a hypervisor. > > If its that way on PPC, than fine for them. But since this is enablement > for x86, it should follow the x86 platform best practices, and that > means describing hardware through ACPI. For hardware, sure. Hypervisors aren't hardware though and a bunch of hypervisors don't use ACPI. > > This "hardware" is actually part of hypervisor so there's no > > reason it can't be completely self-descriptive. It's specified > > by the same entity as the "firmware". > > That is just an implementation detail. Yes, QEMU emulates the hardware > and builds the ACPI tables. But it could also be implemented in a way > where the ACPI tables are build by guest firmware. All these extra levels of indirection is one of the reasons hypervisors such as kata try to avoid ACPI. > > I don't see why it would be much faster. The interface isn't that > > different from command queues of VTD. > > VirtIO IOMMU doesn't need to build page-tables that the hypervisor then > has to shadow, which makes things much faster. If you emulate one of the > other IOMMUs (VT-d or AMD-Vi) the code has to shadow the full page-table > at once when device passthrough is used. VirtIO-IOMMU doesn't need that, > and that makes it much faster and efficient. IIUC VT-d at least supports range invalidations. > > > Making ACPI meet the goals of embedded projects such as kata containers > > would be a gigantic task with huge stability implications. By > > comparison this 400-line parser is well contained and does the job. I > > didn't yet see compelling reasons not to merge this, but I'll be > > interested to see some more specific concerns. > > An ACPI table parse wouldn't need more lines of code. It realies on ACPI OSPM itself to handle ACPI bytecode, which is huge. > For embedded > systems there is still the DT way of describing things. For some embedded systems. > Regards, > > Joerg
