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xen-devel
Re: [Xen-devel] [PATCH] Fix mem.c so that X Windows can restart
On 25 May 2006, at 20:32, Donald D. Dugger wrote:
This patch fixes the problem where you cannot start X Windows on Dom0
after
you have created an HVM guest. The problem is that X uses `mmap' to
map
1 page at physical address 0 with read/write permission. Before an HVM
guest is created this check at around line 1496 of `mm.c':
if ( unlikely((x & (PGT_type_mask|PGT_va_mask)) != type) )
causes the offending code from this patch to be bypassed and X's `mmap'
call works. After an HVM guest is created the check at 1496 of `mm.c'
is
now true and the code from this patch is executed, causing the `mmap'
call to
erroneously fail.
This is totally bogus. That test (line 1496) should *never* be true for
pages that are not type PGT_l*_page_table. I think some HVM code is
indexing frame_table with a zero frame number and then fiddling with
fields in that very first page_info structure. That's very bad -- in
fact it's tempting to add some assertions about page 0 to be tested at
various suitable moments to prevent this sort of bad behaviour.
-- Keir
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