RE: [Xen-users] VIRT to MACHINE conversion

[Security Initiative Team <passrete@xxxxxxxxx>]

In the default mode of operation, doesn't Xen work without SPTs?

The addresses entered into the PTs of the guest are actual machine addresses,
right?
So the PTs remain a virtual-to-machine address mapping,
so where do the (pseudo) physical addresses come into play.

Also, when a guest domain wants to update the PT of a process,
(say to change the permissions from read-only to writable),
what is the exact parameter that it sends to the hypervisor --
page frame number ?



"Petersson, Mats" <Mats.Petersson@xxxxxxx> wrote:
> > > I'm confused about the relation between 
> > > virt and phy addresses in a guest domain?
> > > What is the co-relation between the two?
> > > 
>
> The guest will manage it's own virtual memory mappings. However, those
> are guest physical addresses, so
>  the guest will think that it's got
> 0..256M address range, whilst the machine physical address is, say,
> 256M..512M. 
>
> So there is, essentially, a second level of indirection. This is managed
> by the shadow page table code in Xen - this works in essence by having
> two different page-tables, one that the guest updates, one that is
> maintained by the SPT code. The SPT table will be the one that the
> processor actually uses.

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