Re: [Xen-ia64-devel] EFI Mapping Windows Install Crash Bug

[Simon Horman <horms@xxxxxxxxxxxx>]

On Mon, Jul 07, 2008 at 12:31:20PM +0900, Isaku Yamahata wrote:
> On Wed, Jul 02, 2008 at 05:20:48PM +1000, Simon Horman wrote:
> > On Wed, Jul 02, 2008 at 04:20:33PM +1000, Simon Horman wrote:
> > > On Tue, Jul 01, 2008 at 09:19:24PM +0900, Isaku Yamahata wrote:
> > 
> > [snip]
> > 
> > > > As I'm reviewing the patches, I noticed only xen/arch/ia64/xen/ivt.S
> > > > is patched, but xen/arch/ia64/xen/vmx_ivt.S isn't patched.
> > > > Isn't it necessary to similar change to vmx_ivt.S?
> > > 
> > > [ As per our discussion off-line. ]
> > > 
> > > That is a good question, and one that I wasn't aware of until
> > > you brought it up. I think that the answer is likely no, as
> > > else the code would be very broken, and as it is it does work
> > > most of the time. However, this could just be by chance - for
> > > instance the TLB might be seeded with entries it needs. I
> > > will look into this further.
> > 
> > Hi Yamahata-san,
> > 
> > I believe that the answer to this question is no,
> > there is no need to update the VMX page fault handlers.
> > 
> > As the VHPT is turned off when the EFI RR is active
> > the only page fault handlers that are relevant are
> > vmx_alt_dtlb_miss and vmx_alt_itlb_miss - and emprically
> > from my experience with the non-VMX page fault handlers,
> > itlb misses never occur.
> > 
> > In any case, both vmx_alt_dtlb_miss and vmx_alt_itlb_miss
> > employ the following logic in order to tetermine the
> > physical address (pa) of a faulting address (ifa).
> > 
> > #define IA64_MAX_PHYS_BITS      50
> > pa = ifa & (((1 << IA64_MAX_PHYS_BITS) - 1) & ~0xfff)
> > 
> > The case that we are concerned with is when the ifa
> > looks like 0xe... or 0xc... instead of a normal Xen
> > virtual address which looks like 0xf...
> > 
> > However, the logic above covers all of these cases,
> > and thus the VMX page fault handlers can already
> > identity map EFI memory.
> 
> 
> Yes basically sounds correct.
> It looks like the EFI UC area case isn't handled properly.
> What do you think?

That looks correct to me. I will run some tests with it applied.

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