Re: [PATCH v8 2/8] KVM: Extend the memslot to support fd-based private memory

[Chao Peng]

On Fri, Sep 16, 2022 at 04:14:29PM +0700, Bagas Sanjaya wrote:
> On Thu, Sep 15, 2022 at 10:29:07PM +0800, Chao Peng wrote:
> > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> > index abd7c32126ce..c1fac1e9f820 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.
> 
> Better say "kvm_userspace_memory_region_ext includes all fields of
> kvm_userspace_memory_region struct, while also adds additional fields ..."
> 
> > +
> > +The flags field supports below flags:
> 
> s/below/following/
> 
> > +
> > +- 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.
> > +
> 
> Better say "... For more details, see KVM_GET_DIRTY_LOG."
> 
> > +- 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.
> > +
> 
> Better say "if KVM_CAP_READONLY_MEM allows, KVM_MEM_READONLY makes a new
> slot read-only ..."
> 
> > +- 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.
> >  
> 
> For the lists above,
> s/can be set/

It all looks good, thanks!

> 
> Thanks. 
> 
> -- 
> An old man doll... just what I always wanted! - Clara