Hey Alex and Paolo, I saw there is some code related to AVX https://elixir.bootlin.com/linux/latest/source/arch/x86/kvm/emulate.c#L668
Does that mean in some special cases, kvm supports AVX instructions ? I didn’t really know the big picture, so just guess what it is doing . Thanks, Xu > On Mar 4, 2024, at 6:39 PM, Paolo Bonzini <pbonz...@redhat.com> wrote: > > !-------------------------------------------------------------------| > This Message Is From an External Sender > > |-------------------------------------------------------------------! > > On 3/4/24 22:59, Alex Williamson wrote: >> Since you're not seeing a KVM_EXIT_MMIO I'd guess this is more of a KVM >> issue than QEMU (Cc kvm list). Possibly KVM doesn't emulate vmovdqu >> relative to an MMIO access, but honestly I'm not positive that AVX >> instructions are meant to work on MMIO space. I'll let x86 KVM experts >> more familiar with specific opcode semantics weigh in on that. > > Indeed, KVM's instruction emulator supports some SSE MOV instructions but not > the corresponding AVX instructions. > > Vector instructions however do work on MMIO space, and they are used > occasionally especially in combination with write-combining memory. SSE > support was added to KVM because some operating systems used SSE instructions > to read and write to VRAM. However, so far we've never received any reports > of OSes using AVX instructions on devices that QEMU can emulate (as opposed > to, for example, GPU VRAM that is passed through). > > Thanks, > > Paolo > >> Is your "program" just doing a memcpy() with an mmap() of the PCI BAR >> acquired through pci-sysfs or a userspace vfio-pci driver within the >> guest? >> In QEMU 4a2e242bbb30 ("memory: Don't use memcpy for ram_device >> regions") we resolved an issue[1] where QEMU itself was doing a memcpy() >> to assigned device MMIO space resulting in breaking functionality of >> the device. IIRC memcpy() was using an SSE instruction that didn't >> fault, but didn't work correctly relative to MMIO space either. >> So I also wouldn't rule out that the program isn't inherently >> misbehaving by using memcpy() and thereby ignoring the nature of the >> device MMIO access semantics. Thanks, >> Alex >> [1]https://bugs.launchpad.net/qemu/+bug/1384892 >