[PATCH v7 09/14] KVM: Extend the memslot to support fd-based private memory

[Chao Peng]

Extend the memslot definition to provide guest private memory through a
file descriptor(fd) instead of userspace_addr(hva). Such guest private
memory(fd) may never be mapped into userspace so no userspace_addr(hva)
can be used. Instead add another two new fields
(private_fd/private_offset), plus the existing memory_size to represent
the private memory range. Such memslot can still have the existing
userspace_addr(hva). When use, a single memslot can maintain both
private memory through private fd(private_fd/private_offset) and shared
memory through hva(userspace_addr). Whether the private or shared part
is effective for a guest GPA is maintained by other KVM code.

Since there is no userspace mapping for private fd so we cannot
rely on get_user_pages() to get the pfn in KVM, instead we add a new
memfile_notifier in the memslot and rely on it to get pfn by interacting
the callbacks from memory backing store with the fd/offset.

This new extension is indicated by a new flag KVM_MEM_PRIVATE. At
compile time, a new config HAVE_KVM_PRIVATE_MEM is added and right now
it is selected on X86_64 for Intel TDX usage.

To make KVM easy, internally we use a binary compatible alias struct
kvm_user_mem_region to handle both the normal and the '_ext' variants.

Co-developed-by: Yu Zhang <yu.c.zhang@linux.intel.com>
Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
---
 Documentation/virt/kvm/api.rst | 38 ++++++++++++++++----
 arch/x86/kvm/Kconfig           |  2 ++
 arch/x86/kvm/x86.c             |  2 +-
 include/linux/kvm_host.h       | 13 +++++--
 include/uapi/linux/kvm.h       | 28 +++++++++++++++
 virt/kvm/Kconfig               |  3 ++
 virt/kvm/kvm_main.c            | 64 +++++++++++++++++++++++++++++-----
 7 files changed, 132 insertions(+), 18 deletions(-)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index bafaeedd455c..4f27c973a952 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -1319,7 +1319,7 @@ yet and must be cleared on entry.
 :Capability: KVM_CAP_USER_MEMORY
 :Architectures: all
 :Type: vm ioctl
-:Parameters: struct kvm_userspace_memory_region (in)
+:Parameters: struct kvm_userspace_memory_region(_ext) (in)
 :Returns: 0 on success, -1 on error
 
 ::
@@ -1332,9 +1332,18 @@ yet and must be cleared on entry.
        __u64 userspace_addr; /* start of the userspace allocated memory */
   };
 
+  struct kvm_userspace_memory_region_ext {
+       struct kvm_userspace_memory_region region;
+       __u64 private_offset;
+       __u32 private_fd;
+       __u32 pad1;
+       __u64 pad2[14];
+};
+
   /* for kvm_memory_region::flags */
   #define KVM_MEM_LOG_DIRTY_PAGES      (1UL << 0)
   #define KVM_MEM_READONLY     (1UL << 1)
+  #define KVM_MEM_PRIVATE              (1UL << 2)
 
 This ioctl allows the user to create, modify or delete a guest physical
 memory slot.  Bits 0-15 of "slot" specify the slot id and this value
@@ -1365,12 +1374,27 @@ It is recommended that the lower 21 bits of 
guest_phys_addr and userspace_addr
 be identical.  This allows large pages in the guest to be backed by large
 pages in the host.
 
-The flags field supports two flags: KVM_MEM_LOG_DIRTY_PAGES and
-KVM_MEM_READONLY.  The former can be set to instruct KVM to keep track of
-writes to memory within the slot.  See KVM_GET_DIRTY_LOG ioctl to know how to
-use it.  The latter can be set, if KVM_CAP_READONLY_MEM capability allows it,
-to make a new slot read-only.  In this case, writes to this memory will be
-posted to userspace as KVM_EXIT_MMIO exits.
+kvm_userspace_memory_region_ext includes all the kvm_userspace_memory_region
+fields. It also includes additional fields for some specific features. See
+below description of flags field for more information. It's recommended to use
+kvm_userspace_memory_region_ext in new userspace code.
+
+The flags field supports below flags:
+
+- KVM_MEM_LOG_DIRTY_PAGES can be set to instruct KVM to keep track of writes to
+  memory within the slot.  See KVM_GET_DIRTY_LOG ioctl to know how to use it.
+
+- KVM_MEM_READONLY can be set, if KVM_CAP_READONLY_MEM capability allows it, to
+  make a new slot read-only.  In this case, writes to this memory will be 
posted
+  to userspace as KVM_EXIT_MMIO exits.
+
+- KVM_MEM_PRIVATE can be set to indicate a new slot has private memory backed 
by
+  a file descirptor(fd) and the content of the private memory is invisible to
+  userspace. In this case, userspace should use private_fd/private_offset in
+  kvm_userspace_memory_region_ext to instruct KVM to provide private memory to
+  guest. Userspace should guarantee not to map the same pfn indicated by
+  private_fd/private_offset to different gfns with multiple memslots. Failed to
+  do this may result undefined behavior.
 
 When the KVM_CAP_SYNC_MMU capability is available, changes in the backing of
 the memory region are automatically reflected into the guest.  For example, an
diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index e3cbd7706136..1f160801e2a7 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -48,6 +48,8 @@ config KVM
        select SRCU
        select INTERVAL_TREE
        select HAVE_KVM_PM_NOTIFIER if PM
+       select HAVE_KVM_PRIVATE_MEM if X86_64
+       select MEMFILE_NOTIFIER if HAVE_KVM_PRIVATE_MEM
        help
          Support hosting fully virtualized guest machines using hardware
          virtualization extensions.  You will need a fairly recent
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 567d13405445..77d16b90045c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -12154,7 +12154,7 @@ void __user * __x86_set_memory_region(struct kvm *kvm, 
int id, gpa_t gpa,
        }
 
        for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
-               struct kvm_userspace_memory_region m;
+               struct kvm_user_mem_region m;
 
                m.slot = id | (i << 16);
                m.flags = 0;
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index c262ebb168a7..1b203c8aa696 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -44,6 +44,7 @@
 
 #include <asm/kvm_host.h>
 #include <linux/kvm_dirty_ring.h>
+#include <linux/memfile_notifier.h>
 
 #ifndef KVM_MAX_VCPU_IDS
 #define KVM_MAX_VCPU_IDS KVM_MAX_VCPUS
@@ -576,8 +577,16 @@ struct kvm_memory_slot {
        u32 flags;
        short id;
        u16 as_id;
+       struct file *private_file;
+       loff_t private_offset;
+       struct memfile_notifier notifier;
 };
 
+static inline bool kvm_slot_can_be_private(const struct kvm_memory_slot *slot)
+{
+       return slot && (slot->flags & KVM_MEM_PRIVATE);
+}
+
 static inline bool kvm_slot_dirty_track_enabled(const struct kvm_memory_slot 
*slot)
 {
        return slot->flags & KVM_MEM_LOG_DIRTY_PAGES;
@@ -1109,9 +1118,9 @@ enum kvm_mr_change {
 };
 
 int kvm_set_memory_region(struct kvm *kvm,
-                         const struct kvm_userspace_memory_region *mem);
+                         const struct kvm_user_mem_region *mem);
 int __kvm_set_memory_region(struct kvm *kvm,
-                           const struct kvm_userspace_memory_region *mem);
+                           const struct kvm_user_mem_region *mem);
 void kvm_arch_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot);
 void kvm_arch_memslots_updated(struct kvm *kvm, u64 gen);
 int kvm_arch_prepare_memory_region(struct kvm *kvm,
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index a36e78710382..c467c69b7ad7 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -103,6 +103,33 @@ struct kvm_userspace_memory_region {
        __u64 userspace_addr; /* start of the userspace allocated memory */
 };
 
+struct kvm_userspace_memory_region_ext {
+       struct kvm_userspace_memory_region region;
+       __u64 private_offset;
+       __u32 private_fd;
+       __u32 pad1;
+       __u64 pad2[14];
+};
+
+#ifdef __KERNEL__
+/*
+ * kvm_user_mem_region is a kernel-only alias of 
kvm_userspace_memory_region_ext
+ * that "unpacks" kvm_userspace_memory_region so that KVM can directly access
+ * all fields from the top-level "extended" region.
+ */
+struct kvm_user_mem_region {
+       __u32 slot;
+       __u32 flags;
+       __u64 guest_phys_addr;
+       __u64 memory_size;
+       __u64 userspace_addr;
+       __u64 private_offset;
+       __u32 private_fd;
+       __u32 pad1;
+       __u64 pad2[14];
+};
+#endif
+
 /*
  * The bit 0 ~ bit 15 of kvm_memory_region::flags are visible for userspace,
  * other bits are reserved for kvm internal use which are defined in
@@ -110,6 +137,7 @@ struct kvm_userspace_memory_region {
  */
 #define KVM_MEM_LOG_DIRTY_PAGES        (1UL << 0)
 #define KVM_MEM_READONLY       (1UL << 1)
+#define KVM_MEM_PRIVATE                (1UL << 2)
 
 /* for KVM_IRQ_LINE */
 struct kvm_irq_level {
diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
index a8c5c9f06b3c..ccaff13cc5b8 100644
--- a/virt/kvm/Kconfig
+++ b/virt/kvm/Kconfig
@@ -72,3 +72,6 @@ config KVM_XFER_TO_GUEST_WORK
 
 config HAVE_KVM_PM_NOTIFIER
        bool
+
+config HAVE_KVM_PRIVATE_MEM
+       bool
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 3ae4944b9f15..230c8ff9659c 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1508,7 +1508,7 @@ static void kvm_replace_memslot(struct kvm *kvm,
        }
 }
 
-static int check_memory_region_flags(const struct kvm_userspace_memory_region 
*mem)
+static int check_memory_region_flags(const struct kvm_user_mem_region *mem)
 {
        u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;
 
@@ -1902,7 +1902,7 @@ static bool kvm_check_memslot_overlap(struct kvm_memslots 
*slots, int id,
  * Must be called holding kvm->slots_lock for write.
  */
 int __kvm_set_memory_region(struct kvm *kvm,
-                           const struct kvm_userspace_memory_region *mem)
+                           const struct kvm_user_mem_region *mem)
 {
        struct kvm_memory_slot *old, *new;
        struct kvm_memslots *slots;
@@ -2006,7 +2006,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
 EXPORT_SYMBOL_GPL(__kvm_set_memory_region);
 
 int kvm_set_memory_region(struct kvm *kvm,
-                         const struct kvm_userspace_memory_region *mem)
+                         const struct kvm_user_mem_region *mem)
 {
        int r;
 
@@ -2018,7 +2018,7 @@ int kvm_set_memory_region(struct kvm *kvm,
 EXPORT_SYMBOL_GPL(kvm_set_memory_region);
 
 static int kvm_vm_ioctl_set_memory_region(struct kvm *kvm,
-                                         struct kvm_userspace_memory_region 
*mem)
+                                         struct kvm_user_mem_region *mem)
 {
        if ((u16)mem->slot >= KVM_USER_MEM_SLOTS)
                return -EINVAL;
@@ -4608,6 +4608,33 @@ static int kvm_vm_ioctl_get_stats_fd(struct kvm *kvm)
        return fd;
 }
 
+#define SANITY_CHECK_MEM_REGION_FIELD(field)                                   
\
+do {                                                                           
\
+       BUILD_BUG_ON(offsetof(struct kvm_user_mem_region, field) !=             
\
+                    offsetof(struct kvm_userspace_memory_region, field));      
\
+       BUILD_BUG_ON(sizeof_field(struct kvm_user_mem_region, field) !=         
\
+                    sizeof_field(struct kvm_userspace_memory_region, field));  
\
+} while (0)
+
+#define SANITY_CHECK_MEM_REGION_EXT_FIELD(field)                               
        \
+do {                                                                           
        \
+       BUILD_BUG_ON(offsetof(struct kvm_user_mem_region, field) !=             
        \
+                    offsetof(struct kvm_userspace_memory_region_ext, field));  
        \
+       BUILD_BUG_ON(sizeof_field(struct kvm_user_mem_region, field) !=         
        \
+                    sizeof_field(struct kvm_userspace_memory_region_ext, 
field));      \
+} while (0)
+
+static void kvm_sanity_check_user_mem_region_alias(void)
+{
+       SANITY_CHECK_MEM_REGION_FIELD(slot);
+       SANITY_CHECK_MEM_REGION_FIELD(flags);
+       SANITY_CHECK_MEM_REGION_FIELD(guest_phys_addr);
+       SANITY_CHECK_MEM_REGION_FIELD(memory_size);
+       SANITY_CHECK_MEM_REGION_FIELD(userspace_addr);
+       SANITY_CHECK_MEM_REGION_EXT_FIELD(private_offset);
+       SANITY_CHECK_MEM_REGION_EXT_FIELD(private_fd);
+}
+
 static long kvm_vm_ioctl(struct file *filp,
                           unsigned int ioctl, unsigned long arg)
 {
@@ -4631,14 +4658,35 @@ static long kvm_vm_ioctl(struct file *filp,
                break;
        }
        case KVM_SET_USER_MEMORY_REGION: {
-               struct kvm_userspace_memory_region kvm_userspace_mem;
+               struct kvm_user_mem_region mem;
+               unsigned long size;
+               u32 flags;
+
+               kvm_sanity_check_user_mem_region_alias();
+
+               memset(&mem, 0, sizeof(mem));
 
                r = -EFAULT;
-               if (copy_from_user(&kvm_userspace_mem, argp,
-                                               sizeof(kvm_userspace_mem)))
+
+               if (get_user(flags,
+                       (u32 __user *)(argp + offsetof(typeof(mem), flags))))
+                       goto out;
+
+               if (flags & KVM_MEM_PRIVATE) {
+                       r = -EINVAL;
+                       goto out;
+               }
+
+               size = sizeof(struct kvm_userspace_memory_region);
+
+               if (copy_from_user(&mem, argp, size))
+                       goto out;
+
+               r = -EINVAL;
+               if ((flags ^ mem.flags) & KVM_MEM_PRIVATE)
                        goto out;
 
-               r = kvm_vm_ioctl_set_memory_region(kvm, &kvm_userspace_mem);
+               r = kvm_vm_ioctl_set_memory_region(kvm, &mem);
                break;
        }
        case KVM_GET_DIRTY_LOG: {
-- 
2.25.1