Extend the memslot definition to provide fd-based private memory support
by adding two new fields (private_fd/private_offset). The memslot then
can maintain memory for both shared pages and private pages in a single
memslot. Shared pages are provided by existing userspace_addr(hva) field
and private pages are provided through the new private_fd/private_offset
fields.
Since there is no 'hva' concept anymore for private memory so we cannot
rely on get_user_pages() to get a pfn, instead we use the newly added
memfile_notifier to complete the same job.
This new extension is indicated by a new flag KVM_MEM_PRIVATE.
Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
---
Documentation/virt/kvm/api.rst | 37 +++++++++++++++++++++++++++-------
include/linux/kvm_host.h | 7 +++++++
include/uapi/linux/kvm.h | 8 ++++++++
3 files changed, 45 insertions(+), 7 deletions(-)
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 3acbf4d263a5..f76ac598606c 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -1307,7 +1307,7 @@ 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
::
@@ -1320,9 +1320,17 @@ 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 padding[5];
+};
+
/* 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
@@ -1353,12 +1361,27 @@ 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/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 9536ffa0473b..3be8116079d4 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -563,8 +563,15 @@ struct kvm_memory_slot {
u32 flags;
short id;
u16 as_id;
+ struct file *private_file;
+ loff_t private_offset;
};
+static inline bool kvm_slot_is_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;
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 91a6fe4e02c0..a523d834efc8 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -103,6 +103,13 @@ 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 padding[5];
+};
+
/*
* 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 +117,7 @@ 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 {
--
2.17.1
