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Re: [Xen-devel] [PATCH 08/18] PVH xen: tools changes to create PVH domain

On 30/08/13 10:53, Ian Campbell wrote:
On Thu, 2013-08-29 at 18:24 -0700, Mukesh Rathor wrote:
On Thu, 29 Aug 2013 12:29:44 +0100
Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:

On Thu, 2013-08-29 at 12:13 +0100, George Dunlap wrote:
On Thu, Aug 1, 2013 at 3:02 AM, Mukesh Rathor
<mukesh.rathor@xxxxxxxxxx> wrote:
I'm not sure how you are currently signalling to the hypervisor
that a new domain is a PVH domain? I had a look through this
patch and must be being thick because I don't see it.
I had a flag set, but it was recommended during RFC to remove it.
So, now in xen, a PV with HAP is a PVH guest:
Why was it recommended to remove it?

"PVH == PV + HAP" is a ridiculous interface, and one which will make
it hard to import shadow in the future.  In my series I'm planning
on adding XEN_DOMCTL_CDF_pvh_guest, and using that instead.
These are not stable ABI interfaces, so if someone wants to do PVH
with Shadow then they can just change it.
I thought we named PVH for PV with HAP :)
I thought it was H for HVM myself ;-)

We always talked about an "HVM container", in part to gain back the extra protection levels lost when they took away the segmentation limits for x86-64.

From a Linux maintenance perspective, autotranslate is of course a big win; but there's no reason in principle that we couldn't have used shadow pagetables for that. HAP is a big win in some cases, but a loss in others; it is not, as far as I'm concerned, the primary reason for introducing this mode.


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