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

[Ben Catterall <Ben.Catterall@citrix.com>]

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@citrix.com>
> 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.
>
> Depending on exactly how much memory is needed, you might need to bump
> the default minimum shadow pool size.
>
> ~Andrew
Ok, will do. That will also solve the EPT/NPT problem, thanks!

Ben