Problem statement: Virtual machine crashes when NVIDIA GPU driver access a prefetchable BAR space due to the unaligned reads/writes for pass-through devices. The same binary works fine as expected in the host kernel. Only one BAR has control & status registers (CSR) and other PCI BARs are marked as prefetchable. NVIDIA GPU driver uses the write-combine feature for mapping the prefetchable BARs to improve performance. This problem applies to all other drivers which want to enable WC. Solution: Honor PCI prefetchable attributes for the guest operating systems. Proposal: ARM64-KVM uses VMA struct for the needed information e.g. region physical address, size, and memory-type (struct page backed mapping or anonymous memory) for setting up a stage-2 page table. Right now memory region either can be mapped as DEVICE (strongly ordered) or NORMAL (write-back cache) depends on the flag VM_PFNMAP in VMA. VFIO-PCI will keep the prefetchable (write-combine) information in vma->vm_page_prot similar to other fields, and KVM will prepare stage-2 entries based on the memory-type attribute that was set in VMA. Shanker Donthineni (2): vfio/pci: keep the prefetchable attribute of a BAR region in VMA KVM: arm64: Add write-combine support for stage-2 entries arch/arm64/include/asm/kvm_mmu.h | 3 ++- arch/arm64/include/asm/kvm_pgtable.h | 2 ++ arch/arm64/include/asm/memory.h | 4 +++- arch/arm64/kvm/hyp/pgtable.c | 9 +++++++-- arch/arm64/kvm/mmu.c | 22 +++++++++++++++++++--- arch/arm64/kvm/vgic/vgic-v2.c | 2 +- drivers/vfio/pci/vfio_pci.c | 6 +++++- 7 files changed, 39 insertions(+), 9 deletions(-) -- 2.17.1
