On Fri, Dec 08, 2023 at 10:17:09PM +0530, ankita@xxxxxxxxxx wrote: > arch/arm64/kvm/hyp/pgtable.c | 3 +++ > arch/arm64/kvm/mmu.c | 16 +++++++++++++--- > drivers/vfio/pci/vfio_pci_core.c | 3 ++- > include/linux/mm.h | 7 +++++++ > 4 files changed, 25 insertions(+), 4 deletions(-) It might be worth factoring out the vfio bits into a separate patch together with a bit of documentation around this new vma flag (up to Alex really). > diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c > index d4835d553c61..c8696c9e7a60 100644 > --- a/arch/arm64/kvm/hyp/pgtable.c > +++ b/arch/arm64/kvm/hyp/pgtable.c > @@ -722,6 +722,9 @@ static int stage2_set_prot_attr(struct kvm_pgtable *pgt, enum kvm_pgtable_prot p > kvm_pte_t attr; > u32 sh = KVM_PTE_LEAF_ATTR_LO_S2_SH_IS; > > + if (device && normal_nc) > + return -EINVAL; Ah, the comment Will and I made on patch 1 is handled here. Add a WARN_ON_ONCE() and please move this hunk to the first patch, it makes more sense there. > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > index d14504821b79..1ce1b6d89bf9 100644 > --- a/arch/arm64/kvm/mmu.c > +++ b/arch/arm64/kvm/mmu.c > @@ -1381,7 +1381,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > int ret = 0; > bool write_fault, writable, force_pte = false; > bool exec_fault, mte_allowed; > - bool device = false; > + bool device = false, vfio_pci_device = false; I don't think the variable here should be named vfio_pci_device, the VM_* flag doesn't mention PCI. So just something like "vfio_allow_wc". > unsigned long mmu_seq; > struct kvm *kvm = vcpu->kvm; > struct kvm_mmu_memory_cache *memcache = &vcpu->arch.mmu_page_cache; > @@ -1472,6 +1472,8 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > gfn = fault_ipa >> PAGE_SHIFT; > mte_allowed = kvm_vma_mte_allowed(vma); > > + vfio_pci_device = !!(vma->vm_flags & VM_VFIO_ALLOW_WC); Nitpick: no need for !!, you are assigning to a bool variable already. > diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c > index 1cbc990d42e0..c3f95ec7fc3a 100644 > --- a/drivers/vfio/pci/vfio_pci_core.c > +++ b/drivers/vfio/pci/vfio_pci_core.c > @@ -1863,7 +1863,8 @@ int vfio_pci_core_mmap(struct vfio_device *core_vdev, struct vm_area_struct *vma > * See remap_pfn_range(), called from vfio_pci_fault() but we can't > * change vm_flags within the fault handler. Set them now. > */ > - vm_flags_set(vma, VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP); > + vm_flags_set(vma, VM_VFIO_ALLOW_WC | VM_IO | VM_PFNMAP | > + VM_DONTEXPAND | VM_DONTDUMP); Please add a comment here that write-combining is allowed to be enabled by the arch (KVM) code but the default user mmap() will still use pgprot_noncached(). > vma->vm_ops = &vfio_pci_mmap_ops; > > return 0; > diff --git a/include/linux/mm.h b/include/linux/mm.h > index a422cc123a2d..8d3c4820c492 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -391,6 +391,13 @@ extern unsigned int kobjsize(const void *objp); > # define VM_UFFD_MINOR VM_NONE > #endif /* CONFIG_HAVE_ARCH_USERFAULTFD_MINOR */ > > +#ifdef CONFIG_64BIT > +#define VM_VFIO_ALLOW_WC_BIT 39 /* Convey KVM to map S2 NORMAL_NC */ This comment shouldn't be in the core header file. It knows nothing about S2 and Normal-NC, that's arm64 terminology. You can mention something like VFIO can use this flag hint that write-combining is allowed. > +#define VM_VFIO_ALLOW_WC BIT(VM_VFIO_ALLOW_WC_BIT) > +#else > +#define VM_VFIO_ALLOW_WC VM_NONE > +#endif And I think we need to add some documentation (is there any VFIO-specific doc) that describes what this flag actually means, what is permitted. For example, arm64 doesn't have write-combining without speculative fetches. So if one adds this flag to a new driver, they should know the implications. There's also an expectation that the actual driver (KVM guests) or maybe later DPDK can choose the safe non-cacheable or write-combine (Linux terminology) attributes for the BAR. -- Catalin
