Re: [PATCH v2 REPOST 03/12] x86/mm: add HYPERVISOR_memory_op to acquire guest resources

[Paul Durrant <Paul.Durrant@citrix.com>]

> -----Original Message-----
> From: Wei Liu [mailto:wei.liu2@citrix.com]
> Sent: 28 August 2017 16:01
> To: Paul Durrant <Paul.Durrant@citrix.com>
> Cc: xen-devel@lists.xenproject.org; George Dunlap
> <George.Dunlap@citrix.com>; Andrew Cooper
> <Andrew.Cooper3@citrix.com>; Jan Beulich <jbeulich@suse.com>; Wei Liu
> <wei.liu2@citrix.com>
> Subject: Re: [Xen-devel] [PATCH v2 REPOST 03/12] x86/mm: add
> HYPERVISOR_memory_op to acquire guest resources
> 
> On Tue, Aug 22, 2017 at 03:50:57PM +0100, Paul Durrant wrote:
> > +
> > +/*
> > + * Get the pages for a particular guest resource, so that they can be
> > + * mapped directly by a tools domain.
> > + */
> > +#define XENMEM_acquire_resource 28
> > +struct xen_mem_acquire_resource {
> > +    /* IN - the domain whose resource is to be mapped */
> > +    domid_t domid;
> > +    /* IN - the type of resource (defined below) */
> > +    uint16_t type;
> > +
> > +#define XENMEM_resource_grant_table 0
> > +
> > +    /*
> > +     * IN - a type-specific resource identifier, which must be zero
> > +     *      unless stated otherwise.
> > +     */
> > +    uint32_t id;
> > +    /* IN - number of (4K) frames of the resource to be mapped */
> > +    uint32_t nr_frames;
> > +    /* IN - the index of the initial frame to be mapped */
> > +    uint64_aligned_t frame;
> > +    /* IN/OUT - If the tools domain is PV then, upon return, gmfn_list
> > +     *          will be populated with the MFNs of the resource.
> > +     *          If the tools domain is HVM then it is expected that, on
> > +     *          entry, gmfn_list will be populated with a list of GFNs
> > +     *          that will be mapped to the MFNs of the resource.
> > +     */
> > +    XEN_GUEST_HANDLE(xen_pfn_t) gmfn_list;
> 
> Why is it not possible to make PV does the same thing as HVM?

Because PV guests don't use a P2M as such. An HVM guest can pass GFNs in and say 'I want the resource mapped here'. A PV guest can't do that since it's using MFNs directly... it has to deal with the resource wherever it may be.

  Paul

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