[RFC v2 PATCH 07/13] KVM: Handle page fault for fd based memslot

[Chao Peng]

Current code assume the private memory is persistent and KVM can check
with backing store to see if private memory exists at the same address
by calling get_pfn(alloc=false).

Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
---
 arch/x86/kvm/mmu/mmu.c | 75 ++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 73 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 40377901598b..cd5d1f923694 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3277,6 +3277,9 @@ int kvm_mmu_max_mapping_level(struct kvm *kvm,
        if (max_level == PG_LEVEL_4K)
                return PG_LEVEL_4K;
 
+       if (memslot_is_memfd(slot))
+               return max_level;
+
        host_level = host_pfn_mapping_level(kvm, gfn, pfn, slot);
        return min(host_level, max_level);
 }
@@ -4555,6 +4558,65 @@ static bool kvm_arch_setup_async_pf(struct kvm_vcpu 
*vcpu, gpa_t cr2_or_gpa,
                                  kvm_vcpu_gfn_to_hva(vcpu, gfn), &arch);
 }
 
+static bool kvm_faultin_pfn_memfd(struct kvm_vcpu *vcpu,
+                                 struct kvm_page_fault *fault, int *r)
+{      int order;
+       kvm_pfn_t pfn;
+       struct kvm_memory_slot *slot = fault->slot;
+       bool priv_gfn = kvm_vcpu_is_private_gfn(vcpu, fault->addr >> 
PAGE_SHIFT);
+       bool priv_slot_exists = memslot_has_private(slot);
+       bool priv_gfn_exists = false;
+       int mem_convert_type;
+
+       if (priv_gfn && !priv_slot_exists) {
+               *r = RET_PF_INVALID;
+               return true;
+       }
+
+       if (priv_slot_exists) {
+               pfn = slot->memfd_ops->get_pfn(slot, slot->priv_file,
+                                              fault->gfn, false, &order);
+               if (pfn >= 0)
+                       priv_gfn_exists = true;
+       }
+
+       if (priv_gfn && !priv_gfn_exists) {
+               mem_convert_type = KVM_EXIT_MEM_MAP_PRIVATE;
+               goto out_convert;
+       }
+
+       if (!priv_gfn && priv_gfn_exists) {
+               slot->memfd_ops->put_pfn(pfn);
+               mem_convert_type = KVM_EXIT_MEM_MAP_SHARED;
+               goto out_convert;
+       }
+
+       if (!priv_gfn) {
+               pfn = slot->memfd_ops->get_pfn(slot, slot->file,
+                                              fault->gfn, true, &order);
+               if (fault->pfn < 0) {
+                       *r = RET_PF_INVALID;
+                       return true;
+               }
+       }
+
+       if (slot->flags & KVM_MEM_READONLY)
+               fault->map_writable = false;
+       if (order == 0)
+               fault->max_level = PG_LEVEL_4K;
+
+       return false;
+
+out_convert:
+       vcpu->run->exit_reason = KVM_EXIT_MEMORY_ERROR;
+       vcpu->run->mem.type = mem_convert_type;
+       vcpu->run->mem.u.map.gpa = fault->gfn << PAGE_SHIFT;
+       vcpu->run->mem.u.map.size = PAGE_SIZE;
+       fault->pfn = -1;
+       *r = -1;
+       return true;
+}
+
 static bool kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault 
*fault, int *r)
 {
        struct kvm_memory_slot *slot = fault->slot;
@@ -4596,6 +4658,9 @@ static bool kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct 
kvm_page_fault *fault,
                }
        }
 
+       if (memslot_is_memfd(slot))
+               return kvm_faultin_pfn_memfd(vcpu, fault, r);
+
        async = false;
        fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, false, &async,
                                          fault->write, &fault->map_writable,
@@ -4660,7 +4725,8 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, 
struct kvm_page_fault *fault
        else
                write_lock(&vcpu->kvm->mmu_lock);
 
-       if (fault->slot && mmu_notifier_retry_hva(vcpu->kvm, mmu_seq, 
fault->hva))
+       if (fault->slot && !memslot_is_memfd(fault->slot) &&
+                       mmu_notifier_retry_hva(vcpu->kvm, mmu_seq, fault->hva))
                goto out_unlock;
        r = make_mmu_pages_available(vcpu);
        if (r)
@@ -4676,7 +4742,12 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, 
struct kvm_page_fault *fault
                read_unlock(&vcpu->kvm->mmu_lock);
        else
                write_unlock(&vcpu->kvm->mmu_lock);
-       kvm_release_pfn_clean(fault->pfn);
+
+       if (memslot_is_memfd(fault->slot))
+               fault->slot->memfd_ops->put_pfn(fault->pfn);
+       else
+               kvm_release_pfn_clean(fault->pfn);
+
        return r;
 }
 
-- 
2.17.1