On Mon, Mar 28, 2022 at 09:56:33PM +0000, Sean Christopherson wrote:
> 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 <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;
>
> Peeking ahead, the partial switch to the _ext variant is rather gross. I would
> prefer that KVM use an entirely different, but binary compatible, struct internally.
> And once the kernel supports C11[*], I'm pretty sure we can make the "region" in
> _ext an anonymous struct, and make KVM's internal struct a #define of _ext. That
> should minimize the churn (no need to get the embedded "region" field), reduce
> line lengths, and avoid confusion due to some flows taking the _ext but others
> dealing with only the "base" struct.
Will try that.
>
> Maybe kvm_user_memory_region or kvm_user_mem_region? Though it's tempting to be
> evil and usurp the old kvm_memory_region :-)
>
> E.g. pre-C11 do
>
> struct kvm_userspace_memory_region_ext {
> struct kvm_userspace_memory_region region;
> __u64 private_offset;
> __u32 private_fd;
> __u32 padding[5];
> };
>
> #ifdef __KERNEL__
> struct kvm_user_mem_region {
> __u32 slot;
> __u32 flags;
> __u64 guest_phys_addr;
> __u64 memory_size; /* bytes */
> __u64 userspace_addr; /* start of the userspace allocated memory */
> __u64 private_offset;
> __u32 private_fd;
> __u32 padding[5];
> };
> #endif
>
> and then post-C11 do
>
> struct kvm_userspace_memory_region_ext {
> #ifdef __KERNEL__
Is this #ifndef? As I think anonymous struct is only for kernel?
Thanks,
Chao
> struct kvm_userspace_memory_region region;
> #else
> struct kvm_userspace_memory_region;
> #endif
> __u64 private_offset;
> __u32 private_fd;
> __u32 padding[5];
> };
>
> #ifdef __KERNEL__
> #define kvm_user_mem_region kvm_userspace_memory_region_ext
> #endif
>
> [*] https://lore.kernel.org/all/20220301145233.3689119-1-arnd@xxxxxxxxxx
>
> > + __u64 private_offset;
> > + __u32 private_fd;
> > + __u32 padding[5];
> > +};
