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

[Bagas Sanjaya]

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/

Thanks. 

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

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