[PATCH] xen/ia64 memory_exchange work around (was Re: [Xen-ia64-devel] steal_page(MEMF_no_refcount) page->count_info no longer consistent)

[Isaku Yamahata <yamahata@xxxxxxxxxxxxx>]

Here is the work around patch. I was able to boot dom0 with this patch.
The right fix is to modify memory_exchange() to be aware of 
ia64 page reference count convention, and convince x86 developper.
Since It may take a while, I sent this work around patch.


On Thu, Mar 01, 2007 at 07:29:58PM +0900, Isaku Yamahata wrote:
> On Thu, Mar 01, 2007 at 11:59:27AM +0900, Isaku Yamahata wrote:
> > On Wed, Feb 28, 2007 at 04:55:27PM -0700, Alex Williamson wrote:
> > 
> > >    Current xen-unstable.hg tip has a problem booting dom0 that I'd like
> > > your opinion on.  We're failing the check in steal_page() that ensures
> > > that count_info is 2 when called with the MEMF_no_refcount flag.  In
> > > fact, it seems that steal_page() is now getting called for pages that
> > > have a count_info of 1 or 2.  Are we being overly paranoid with this
> > > check, or is this an indication of a deeper problem?  The change seems
> > > to have been introduced by the recent memory allocator changes which
> > > removed the bit width restrictions.  Thanks,
> > 
> > By the coarse code check, I couldn't find the case that count_info = 1
> > with MEMF_no_refcount can occur.
> > The reference count semantics seems to have been changed in a subtle way.
> > I'll try to reproduce it and take a deeper look into it.
> 
> I found the root cause.
> In fact XENMEM_exchange(memory_exchange()) has been broken on ia64.
> Especially when memory_exchange() failed, page->count_info
> is left in broken state (= PGC_allocated | 1).
> The next time XENMEM_exchange hypercall is called, the message is printed out.
> Probably we have to revise memory_exchange() in common code and
> convince x86 developers.
> 
> So the temporal work around might be necessary.
> The trigger is c/s 13366:ed73ff8440d8 in xen-unstable.hg.
> swiotlb_init_with_default_size() was changed to pass
> dma address bits which causes XENMEM_exchange fail.
> The easy temporal work around is to modify swiotlb_init_with_default_size().
> -- 
> yamahata
> 
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> 

-- 
yamahata

Attachment: 14175_daca4d71d826_xen_ia64_xenmem_exchange_bug_work_around.patch
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