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

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 4/10/06 14:47, "Rik van Riel" <riel@xxxxxxxxxx> wrote:

>> 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 should use pte_pfn(), or pte_mfn(), or (pte_val() & PHYSICAL_PAGE_MASK)
for isolating the address part of a pte. If there is *any* Linux code that
is accessing addresses from pte contents via other methods then please do
let us know! But I suspect this won't be the case, due to the existing need
to mask off PAGE_NX.

 -- Keir



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