[Xen-devel] Re: invalid PTE for xen_start-info ?

[Rik van Riel <riel@xxxxxxxxxx>]

Keir Fraser wrote:
> On 3/10/06 7:06 pm, "Rik van Riel" <riel@xxxxxxxxxx> wrote:
>
> > pte 0000000019800027 (real 0010000035010027)
> >
> > That last PTE value does not look like a valid x86-64 PTE
> > value to me.  That high bit is not the NX bit, nor is it
> > within the physical address range of the system in question.
> >
> > What's going on here?
> >
> > Is this a bug you would like a fix for?
> It's not a bug -- it's one of the available-for-software flags that is
> stolen by Xen to indicate a kernel PTE. This is done so that we can
> distinguish kernel and user mappings, so that the latter can have the global
> bit set. Sounds weird, but it avoids flushing user mappings from the TLB
> when executing syscalls (we have to change %cr3 value when switching between
> guest-user and guest-kernel modes).
OK, so pte_val() just needs to know about these software flags
and mask them out before passing the value to mfn_to_pfn ?

--
"You don't have to be crazy to do this... but it helps." -- Bob Ross

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