Hi, > That will bring back all issues with cached vs non-cached memory accesses, > no? So edk2 will always access that memory as device memory which means it > bypasses the cache, while QEMU will access it through the cache. So that > buffer would need to actually be MMIO memory I suppose?
I don't think so. The firmware driver knows this actually is normal ram and can setup mappings and memory attributes accordingly. The situation is a bit different from vga memory bars which are handled by pci bus management which doesn't know anything about virtualization specifics. Well, unless macos thinks it knows everything better and goes setup uncached mappings ... > > Not sure how to do that best on x86 though. Find 64k unused address > > space over ioapic? Do we have enough free space there? And how > > future-proof would that be? > > I'm not worried yet about where we place that memory, but more about > ensuring that we actually have a working path to access it. We can always > find space in the PCI hole, as long as we properly advertise it to all > stakeholders via ACPI and memory map. Well, the host can't easily place stuff in the pci hole because the guest will manage that (map pci bars etc). But making the pci hole a bit smaller to make room is an option I think. take care, Gerd
