On Wed, 2008-03-12 at 09:44 -0700, Jeremy Fitzhardinge wrote:
> Martin Schwidefsky wrote:
> > That is the first block of state transitions: {Ur,Sr,Vr,Pr}
> > You can go from any of the four states to any of the remaining three.
> >
>
> You only mention page_set_{unused,stable,volatile}. Is
> page_set_stable_if_present() the fourth. And shouldn't that be
> "stable_if_clean":
page_set_volatile has a "writable" argument. For writable==0 you get a
Vx page, for writable==1 you get a Px page.
With stable_if_clean you are refering to stable_if_present? If yes the
answer is that this operation is used to get a page from Vx/Px back to
Sx but only if the page has not been discarded. The operation will fail
if the page state is Vz/Pz. The dirty bit only matters for the hosts
decision to discard the page, these are the state transitions from Vr/Pr
to Vz.
> - potential volatile (P): the page has useful content. The host system
> is allowed to discard the content after it has checked the dirty bit
> of the page. It has to deliver a discard fault with the absolute
> address of the page if the guest tries to access it.
>
>
> The use of "stable" in the function call and "volatile" in this
> description is a bit confusing. My understanding is that a page in this
> state is either stable or volatile depending on whether its dirty, which
> makes sense, but it would be good to consistently refer to it in the
> same way.
Your understanding is good, but how can I make this less confusing? A Px
page that is dirty may not be discarded which makes it basically stable.
The guest state still is potential volatile though as it does not have a
state of Sx.
--
blue skies,
Martin.
"Reality continues to ruin my life." - Calvin.
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