[PATCH v3 15/15] KVM: Register/unregister private memory slot to memfd

[Chao Peng]

Expose KVM_MEM_PRIVATE flag and register/unregister private memory
slot to memfd when userspace sets the flag.

KVM_MEM_PRIVATE is disallowed by default but architecture code can
turn it on by implementing kvm_arch_private_memory_supported().

Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
---
 include/linux/kvm_host.h |  2 ++
 virt/kvm/kvm_main.c      | 35 +++++++++++++++++++++++++++++++----
 2 files changed, 33 insertions(+), 4 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 0c53df0a6b2e..0f0e24f19892 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1096,6 +1096,8 @@ int kvm_arch_post_init_vm(struct kvm *kvm);
 void kvm_arch_pre_destroy_vm(struct kvm *kvm);
 int kvm_arch_create_vm_debugfs(struct kvm *kvm);
 bool kvm_arch_dirty_log_supported(struct kvm *kvm);
+bool kvm_arch_private_memory_supported(struct kvm *kvm);
+
 
 #ifndef __KVM_HAVE_ARCH_VM_ALLOC
 /*
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 79313c549fb9..6eb0d86abdcf 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1509,6 +1509,11 @@ bool __weak kvm_arch_dirty_log_supported(struct kvm *kvm)
        return true;
 }
 
+bool __weak kvm_arch_private_memory_supported(struct kvm *kvm)
+{
+       return false;
+}
+
 static int check_memory_region_flags(struct kvm *kvm,
                             const struct kvm_userspace_memory_region_ext *mem)
 {
@@ -1517,6 +1522,9 @@ static int check_memory_region_flags(struct kvm *kvm,
        if (kvm_arch_dirty_log_supported(kvm))
                valid_flags |= KVM_MEM_LOG_DIRTY_PAGES;
 
+       if (kvm_arch_private_memory_supported(kvm))
+               valid_flags |= KVM_MEM_PRIVATE;
+
 #ifdef __KVM_HAVE_READONLY_MEM
        valid_flags |= KVM_MEM_READONLY;
 #endif
@@ -1708,9 +1716,21 @@ static int kvm_set_memslot(struct kvm *kvm,
        /* Copy the arch-specific data, again after (re)acquiring 
slots_arch_lock. */
        memcpy(&new->arch, &old.arch, sizeof(old.arch));
 
+       if (mem->flags & KVM_MEM_PRIVATE && change == KVM_MR_CREATE) {
+               r = kvm_memfd_register(kvm, mem, new);
+               if (r)
+                       goto out_slots;
+       }
+
        r = kvm_arch_prepare_memory_region(kvm, new, mem, change);
-       if (r)
+       if (r) {
+               if (mem->flags & KVM_MEM_PRIVATE && change == KVM_MR_CREATE)
+                       kvm_memfd_unregister(kvm, new);
                goto out_slots;
+       }
+
+       if (mem->flags & KVM_MEM_PRIVATE && change == KVM_MR_DELETE)
+               kvm_memfd_unregister(kvm, new);
 
        update_memslots(slots, new, change);
        slots = install_new_memslots(kvm, as_id, slots);
@@ -1786,10 +1806,12 @@ int __kvm_set_memory_region(struct kvm *kvm,
                return -EINVAL;
        if (mem->guest_phys_addr & (PAGE_SIZE - 1))
                return -EINVAL;
-       /* We can read the guest memory with __xxx_user() later on. */
        if ((mem->userspace_addr & (PAGE_SIZE - 1)) ||
-           (mem->userspace_addr != untagged_addr(mem->userspace_addr)) ||
-            !access_ok((void __user *)(unsigned long)mem->userspace_addr,
+           (mem->userspace_addr != untagged_addr(mem->userspace_addr)))
+               return -EINVAL;
+       /* We can read the guest memory with __xxx_user() later on. */
+       if (!(mem->flags & KVM_MEM_PRIVATE) &&
+           !access_ok((void __user *)(unsigned long)mem->userspace_addr,
                        mem->memory_size))
                return -EINVAL;
        if (as_id >= KVM_ADDRESS_SPACE_NUM || id >= KVM_MEM_SLOTS_NUM)
@@ -1821,6 +1843,8 @@ int __kvm_set_memory_region(struct kvm *kvm,
        new.npages = mem->memory_size >> PAGE_SHIFT;
        new.flags = mem->flags;
        new.userspace_addr = mem->userspace_addr;
+       new.file = NULL;
+       new.file_ofs = 0;
 
        if (new.npages > KVM_MEM_MAX_NR_PAGES)
                return -EINVAL;
@@ -1829,6 +1853,9 @@ int __kvm_set_memory_region(struct kvm *kvm,
                change = KVM_MR_CREATE;
                new.dirty_bitmap = NULL;
        } else { /* Modify an existing slot. */
+               /* Private memslots are immutable, they can only be deleted. */
+               if (mem->flags & KVM_MEM_PRIVATE)
+                       return -EINVAL;
                if ((new.userspace_addr != old.userspace_addr) ||
                    (new.npages != old.npages) ||
                    ((new.flags ^ old.flags) & KVM_MEM_READONLY))
-- 
2.17.1