Re: [PATCH v5 05/13] KVM: Extend the memslot to support fd-based private memory
From: Sean Christopherson <seanjc@google.com>
Date: 2022-03-28 21:28:31
Also in:
kvm, linux-fsdevel, linux-mm, lkml, qemu-devel
On Thu, Mar 10, 2022, Chao Peng wrote:
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 <redacted>
Needs a Co-developed-by: for Yu, or a From: if Yu is the sole author.
quoted hunk ↗ jump to hunk
Signed-off-by: Chao Peng <redacted> --- 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];
Uber nit, I'd prefer we pad u32 for private_fd separate from padding the size of the structure for future expansion. Regarding future expansion, any reason not to go crazy and pad like 128+ bytes? It'd be rather embarassing if the next memslot extension needs 3 u64s and we end up with region_ext2 :-)
+}; + /* 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
...
+static inline bool kvm_slot_is_private(const struct kvm_memory_slot *slot)
I 100% think we should usurp the name "private" for these memslots, but as prep work this series should first rename KVM_PRIVATE_MEM_SLOTS to avoid confusion. Maybe KVM_INTERNAL_MEM_SLOTS?