Re: [PATCH v6 01/43] KVM: guest_memfd: Introduce per-gmem attributes, use to guard user mappings

[Ackerley Tng]

Ackerley Tng via B4 Relay <devnull+ackerleytng.google.com@xxxxxxxxxx>
writes:

>
> [...snip...]
>
> diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
> index 69c9d6d546b28..5011d38820d0d 100644
> --- a/virt/kvm/guest_memfd.c
> +++ b/virt/kvm/guest_memfd.c
> @@ -4,6 +4,7 @@
>  #include <linux/falloc.h>
>  #include <linux/fs.h>
>  #include <linux/kvm_host.h>
> +#include <linux/maple_tree.h>
>  #include <linux/mempolicy.h>
>  #include <linux/pseudo_fs.h>
>  #include <linux/pagemap.h>
> @@ -33,6 +34,13 @@ struct gmem_inode {
>  	struct list_head gmem_file_list;
>
>  	u64 flags;
> +	/*
> +	 * Every index in this inode, whether memory is populated or
> +	 * not, is tracked in attributes. The entire range of indices,
> +	 * corresponding to the size of this inode, is represented in
> +	 * this maple tree.

Concretely, if the entire guest_memfd is 2M in size, indices [0, 511] is
represented with some value, either 0 (SHARED) or
KVM_MEMORY_ATTRIBUTE_PRIVATE. [512, ULONG_MAX] is also defined in the
tree, as NULL.

Since guest_memfd uses xa_mk_value(0) to store the value 0 ("SHARED"),
that makes 0 distinct from NULL, which works for guest_memfd.


(Liam and I discussed this off-list due to a email configuration issue)

> +	 */
> +	struct maple_tree attributes;
>  };
>
>
> [...snip...]
>