Re: [patch 14/21] Xen-paravirt: Add XEN config options anddisableunsupported config options.

[Andrew Morton]

On Fri, 16 Feb 2007 10:47:11 +0000 Keir Fraser <keir@xxxxxxxxxxxxx> wrote:

> On 16/2/07 10:09, "Andrew Morton" <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> 
> > Are the places where the domU code references machine addresses splattered
> > all over the code?  If not, they can just be wrapped with
> > preempt_disable/preempt_enable?
> 
> The main places where machine addresses are 'visible' are any code that
> holds a pte_t,pmd_t,pud_t,pgd_t. We hide the machine-to-pseudophysical and
> pseudophysical-to-machine translations inside e.g., pte_val() and __pte()
> (i.e., constructors and extractors for page table entries). Obviously the
> users of these macros are open coded all over the place, quite apart from
> the performance cost of sprinkling preempt_{enable,disable} so liberally.

OK, you're screwed.  I agree that the process freezer is the way out of that one.

Ingo said that he's clocked the freezer at a few milliseconds.  But if it's
any higher than that it'll need to get sped up once we convert cpu hotplug
to use it.
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