elax stage2 mapping from hardcoded DEVICE_nGnRE to Normal-NC for vfio-pci devices via an opt-in VMA flag (VM_ALLOW_ANY_UNCACHED). This restores guest control over device MMIO attributes, enabling write-combining (Normal-NC) when requested by guest drivers. DEVICE_nGnRE is not safer than Normal-NC; platform safety depends on PCIe AER/DPC containment, not stage2 type. Performance: mlx5 RDMA VFIO latency improves from ~2.95us to ~2.45us (bare-metal level) as BlueFlame doorbell WC becomes effective. Non-PCI devices (e.g. GICv2) unaffected. Ankit Agrawal (4): KVM: arm64: Introduce new flag for non-cacheable IO memory mm: Introduce new flag to indicate wc safe KVM: arm64: Set io memory s2 pte as normalnc for vfio pci device vfio: Convey kvm that the vfio-pci device is wc safe arch/arm64/include/asm/kvm_pgtable.h | 4 +++- arch/arm64/include/asm/memory.h | 2 ++ arch/arm64/kvm/hyp/pgtable.c | 24 +++++++++++++++++++----- arch/arm64/kvm/mmu.c | 14 ++++++++++---- drivers/vfio/pci/vfio_pci_core.c | 19 ++++++++++++++++++- include/linux/mm.h | 14 ++++++++++++++ 6 files changed, 66 insertions(+), 11 deletions(-) -- 2.33.0