Re: reserve e820 ram

[Francisco Rocha <f.e.liberal-rocha@newcastle.ac.uk>]

On 04/18/2012 05:43 PM, Tim Deegan wrote:
>
> At 15:36 +0100 on 18 Apr (1334763404), Francisco Rocha wrote:
> > Hi Tim,
> >
> > I was thinking about changing my approach.
> >
> > I think that for now I will leave those pages off because I am
> > mostly interested in protecting other areas.
> >
> > Those accesses for now are inevitable to get the VM to properly
> > operate. Now, the question is if it is possible to use page table
> > entries to do what I want to do.
> >
> > The objective would be to use a bit flag that would determine if
> > the pages are returned when a call to map_foreign_range is made.
> > So, my final objective would be that only pages used for the three
> > operations you describe are accessible to Dom0.
> > Everything that is not BIOS and related, Qemu or PV backend
> > drivers will not be returned.
> >
> > From what I see in the header files you use 12-bits from a 24-bit
> > flag (x86_64). Can we do it? This would again take us to controlling
> > access at get_page_from_l1e(), right?
>
> Are you talking about the count_info and type_info fields?  yes, I think
> you can probably put a new flag or two in there.
>
I was thinking about the ones used in page table entries
(_PAGE_PRESENT|RW, etc). So, I can do the type of control
I want to achieve using type_info, maybe the flags I was
thinking about are not the best option for what I want.
>
> Choosing which pages
> qemu can map will be interesting, though -- it needs to map anything the
> VM uses for I/O.  But maybe you can just define the things you protect
> and declare taht they can't be used for I/O.  That sounds easier. :)
>
The objective is to protect the kernel and its data structures.
That is why I was considering the flags I previously mentioned.
There is one denominated _PAGE_GUEST_KERNEL.

I see that we have them all available.

int get_page_from_l1e(...)
...
     struct page_info *page = mfn_to_page(mfn);
     uint32_t l1f = l1e_get_flags(l1e);
...

Which flags do you recommend I use to try this out?
>
>
> Cheers,
>
> Tim.
>
>
Thank you,
Francisco