Re: [Xen-devel] 32bit PAE PV guest on 64bit hypervisor

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

Keir Fraser wrote:
> On 14/04/2009 04:39, "Mukesh Rathor" <mukesh.rathor@xxxxxxxxxx> wrote:
..
> Implementing clear_fixmap() with set_pte() is not correct, even on native.
> Since it clears high then low, it temporarily leaves you with a possibly
> invalid present PTE -- even on native this can cause problems if e.g., the
> invalid PTE maps uncacheable I/O memory.
>
> In our kernel we simply solved this by implementing __set_fixmap() with a
> hypercall that could update all 64 bits at once. An alternative is indeed to
> clear low then high. Basically, clearing a pte has to be done the opposite
> way round to setting a pte.
>
>  -- Keir
Just a quick update, I changed to hypercall and it worked.  BTW, I also had to 
increase the __PHYSICAL_MASK_SHIFT in guest (to 40) as I'm on system with 
128GB. With both changes in the 32bit PAE guest, it's doing OK now.
Thanks for the help.
Mukesh


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