Re: [Xen-devel] [RFC XEN PATCH v4 00/41] Add vNVDIMM support to HVM domains

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Tue, Feb 13, 2018 at 04:05:45AM -0700, Jan Beulich wrote:
> >>> On 13.02.18 at 11:29, <roger.pau@xxxxxxxxxx> wrote:
> > On Tue, Feb 13, 2018 at 03:06:24AM -0700, Jan Beulich wrote:
> >> >>> On 12.02.18 at 11:05, <roger.pau@xxxxxxxxxx> wrote:
> >> > If you map the NVDIMM as MMIO to Dom0 you don't need the M2P entries
> >> > IIRC, and if it's mapped using 1GB pages it shouldn't use that much
> >> > memory for the page tables (ie: you could just use normal RAM for the
> >> > page tables that map the NVDIMM IMO). Of course that only applies to
> >> > PVH/HVM.
> >> 
> >> But in order to use (part of) it in a RAM-like manner we need struct
> >> page_info for it.
> > 
> > I guess the main use of this would be to grant NVDIMM pages? And
> > without a page_info that's not possible.
> 
> Why grant? Simply giving such a page as RAM to a guest would
> already be a problem without struct page_info (as then we can't
> track the page owner, nor can we refcount the page).

My point was to avoid doing that, and always assign the pages as
MMIO, which IIRC doesn't require a struct page_info.

Roger.

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