Re: [Xen-devel] [PATCH 05/16] vmx: nest: virtual vmcs layout

[Tim Deegan <Tim.Deegan@xxxxxxxxxx>]

At 16:22 +0100 on 08 Sep (1283962933), Qing He wrote:
> + * Since physical VMCS layout is unknown, a custom layout is used
> + * for virtual VMCS seen by guest. It occupies a 4k page, and the
> + * field is offset by an 9-bit offset into u64[], The offset is as
> + * follow, which means every <width, type> pair has a max of 32
> + * fields available.

A question - is this layout likely to have to change often in future?
(I guess the answer's no but you'll know best.)  We'll have to carry
compatibility code indefinitely so that VMs can be migrated to newer
Xens without breaking.

> + *             9       7      5               0
> + *             --------------------------------
> + *     offset: | width | type |     index     |
> + *             --------------------------------
> + *
> + * Also, since the lower range <width=0, type={0,1}> has only one
> + * field: VPID, it is moved to a higher offset (63), and leaves the
> + * lower range to non-indexed field like VMCS revision.
> + *
> + */
> +
> +#define VVMCS_REVISION 0x40000001u
> +
> +struct vvmcs_header {
> +    u32 revision;
> +    u32 abort;
> +};

This structure isn't used anywhere in the rest of the patch series.
Oversight?

Cheers,

Tim.

-- 
Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Principal Software Engineer, XenServer Engineering
Citrix Systems UK Ltd.  (Company #02937203, SL9 0BG)

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