[RFC PATCH 08/30] KVM: x86/mmu: Handle page fault for vfio_dmabuf backed MMIO

[Xu Yilun]

Add support for resolving page faults on vfio_dmabuf backed MMIO. Now
only support setup KVM MMU mapping on shared roots, i.e. vfio_dmabuf
works for shared assigned devices.

Further work is to support private MMIO for private assigned
devices (known as TDI in TDISP spec).

Signed-off-by: Xu Yilun <yilun.xu at linux.intel.com>
---
 arch/x86/kvm/mmu/mmu.c   | 16 ++++++++++++++++
 include/linux/kvm_host.h |  5 +++++
 2 files changed, 21 insertions(+)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 63bb77ee1bb1..40d33bd6b532 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4523,6 +4523,22 @@ static int __kvm_mmu_faultin_pfn(struct kvm_vcpu *vcpu,
 	if (fault->is_private)
 		return kvm_mmu_faultin_pfn_private(vcpu, fault);
 
+	/* vfio_dmabuf slot is also applicable for shared mapping */
+	if (kvm_slot_is_vfio_dmabuf(fault->slot)) {
+		int max_order, r;
+
+		r = kvm_vfio_dmabuf_get_pfn(vcpu->kvm, fault->slot, fault->gfn,
+					    &fault->pfn, &max_order);
+		if (r)
+			return r;
+
+		fault->max_level = min(kvm_max_level_for_order(max_order),
+				       fault->max_level);
+		fault->map_writable = !(fault->slot->flags & KVM_MEM_READONLY);
+
+		return RET_PF_CONTINUE;
+	}
+
 	foll |= FOLL_NOWAIT;
 	fault->pfn = __kvm_faultin_pfn(fault->slot, fault->gfn, foll,
 				       &fault->map_writable, &fault->refcounted_page);
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index d16f47c3d008..b850d3cff83c 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -623,6 +623,11 @@ static inline bool kvm_slot_can_be_private(const struct kvm_memory_slot *slot)
 	return slot && (slot->flags & KVM_MEM_GUEST_MEMFD);
 }
 
+static inline bool kvm_slot_is_vfio_dmabuf(const struct kvm_memory_slot *slot)
+{
+	return slot && (slot->flags & KVM_MEM_VFIO_DMABUF);
+}
+
 static inline bool kvm_slot_dirty_track_enabled(const struct kvm_memory_slot *slot)
 {
 	return slot->flags & KVM_MEM_LOG_DIRTY_PAGES;
-- 
2.25.1