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Re: [PATCH] fix ia64 breakage with PHYSDEVOP_pirq_eoi_mfn (was Re: [Xen-devel] [PATCH 2/2] linux/x86: use shared page indicating the need for an EOI notification)

On Tue, Dec 09, 2008 at 10:04:55AM +0000, Jan Beulich wrote:
> >>> Isaku Yamahata <yamahata@xxxxxxxxxxxxx> 09.12.08 04:40 >>>
> >Sorry for breakage.
> >How about moving arbitrary_virt_to_machine() from pgtable.h to maddr.h?
> >(Yes, this is a work around. and you wouldn't like it...)
> No, that wouldn't work for x86 either, because the macro uses
> lookup_address(), which in turn is also only declared in pgtable.h. I
> wouldn't really mind moving arbitrary_virt_to_machine(), but it would
> then require duplicating (not moving) the lookup_address() declaration.
> >> Looking at how ia64 defines virt_to_machine() at present I would be
> >> inclined to say that all current users (tpmfront, blktap, and gntdev) of
> >> that macro don't get what they expect, and the implementation you
> >> added for arbitary_virt_to_machine() really ought to be the one for
> >> virt_to_machine(), given your description above.
> >
> >Looking the x86 virt_to_machine definition, virt_to_machine()
> >assumes the passed address in the straight mapping area.
> >So the ia64 assumption is same to x86.
> Not exactly: Addresses of kernel objects *can* be passed to
> virt_to_machine() on x86 (minus a supposed compiler issue demanding
> the special __pa_symbol() to be used on x86-64 - I'm trying to find out
> how relevant this still is), but they can't be on ia64. This is what seemed
> wrong to me. But otoh as I understand it you can't pass kernel
> addresses through __pa() either, but (to my surprise) ia64 apparently
> has no problem with this wrt architecture independent code (but making
> necessary work-arounds like paddr_vmcoreinfo_note()).

You are the first person to pass the kernel symbol address
to virt_to_machine() in arch independent code.
Is there any necessity to allocate pirq_needs_eoi statically?
(except it did before)
If no, can we allocate the pages for them dynamically?
Then the issue will go away.

> >Hmm, ia64 and x86_64 have nothing to do with highmem,
> >but x86_32 has to deal with highmem. So x86_32 with highmem
> >seems to have the issue you described above.
> >If ptep which is passed to virt_to_machine is highmem,
> >I don't see how it works. So all virt_to_machine() shouldn't
> >be changed to arbitrary_virt_to_machine()?
> Actually, looking at it a second time, tpmfront uses the result of the result
> of __get_free_page() here, so the address is always in the 1:1 mapping.
> But I think you're quite right about the HIGHPTE implications on blktap and
> gntdev - these ought to be fixed, perhaps indeed by using
> arbitrary_virt_to_machine() there (but I'd want to make this conditional
> upon the HIGHPTE config option, so to not affect performance of other
> configurations: possibly this ought to be an architecture-defined macro
> like ptep_virt_to_machine(), as I wouldn't want to place an x86-specific
> conditional in there that would risk breaking any future supported
> architecture without explicit notice).

Introduce ptep_to_machine() or something like that?


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