Re: [Xen-devel] [RFC 1/4] HVM x86 deprivileged mode: Page allocation helper

[Tim Deegan <tim@xxxxxxx>]

At 09:50 +0100 on 10 Aug (1439200241), Tim Deegan wrote:
> Hi,
> 
> At 10:57 +0100 on 07 Aug (1438945038), Ben Catterall wrote:
> > On 06/08/15 20:22, Andrew Cooper wrote:
> > > On 06/08/15 17:45, Ben Catterall wrote:
> > >> This allocation function is used by the deprivileged mode initialisation 
> > >> code
> > >> to allocate pages for the new page table mappings and page frames on the 
> > >> HAP
> > >> page heap.
> > >>
> > >> Signed-off-by: Ben Catterall <Ben.Catterall@xxxxxxxxxx>
> > > This is fine for your test box, but isn't fine for systems out there
> > > without hardware EPT/NPT support.  For older systems like that (or in
> > > certain specific workloads), shadow paging is used instead.
> > >
> > > This feature is applicable to any HVM domain, which means that it
> > > shouldn't depend on HAP or shadow paging.
> > >
> > > How much memory is allocated for the depriv area, and what exactly is
> > > allocated in total?
> > So, per-vcpu:
> > - a user mode stack which, from your comments in [RFC 2/4], can be 2 pages
> > - local data (may or may not be needed, depends on the device) which 
> > will be around
> >    a page or two.
> > 
> > Text segment: as per your comments in RFC 2/4, this will be changed to 
> > be an alias
> > so no extra memory.
> > > I expect it isn't very much, and would suggest using
> > > d->arch.paging.alloc_page() instead (which is the generic "get me some
> > > memory accounted against the domain" helper) which looks as if it should
> > > suffice.
> 
> Whie I agree that it would be good to account this to the domain,
> paging->alloc_page() is an internal _paging assistance_ helper. :)
> This new allocation is nothing to do with mm/paging-assistance, so
> either it should find its own memory or the hap/shadow pool needs to
> be made more generic.

...at which point other HVM overheads - VMCx pages, bitmaps &c - could
be allocated from it as well.

Cheers,

Tim.

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