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author | Keir Fraser <keir.fraser@citrix.com> | 2010-09-01 10:17:49 +0100 |
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committer | Keir Fraser <keir.fraser@citrix.com> | 2010-09-01 10:17:49 +0100 |
commit | bdb5439c3f5d1dbf50a149c6ecb1cbdd1d3b182d (patch) | |
tree | 8e214a48419c42663c79a3d1e23acde229ba20de /xen/arch/x86/x86_64/mm.c | |
parent | 4e3645c1b018f7a48b1bdfccca04a3b9008af1e9 (diff) | |
download | xen-bdb5439c3f5d1dbf50a149c6ecb1cbdd1d3b182d.tar.gz xen-bdb5439c3f5d1dbf50a149c6ecb1cbdd1d3b182d.tar.bz2 xen-bdb5439c3f5d1dbf50a149c6ecb1cbdd1d3b182d.zip |
x86_64: Ensure frame-table compression leaves MAX_ORDER aligned
contiguous ranges of page_info structs. This allows page-pointer
arithmetic in places like our buddy allocator.
This restriction was already implicitly guaranteed, but it is good to
make it explicit in the pdx-related initialisation.
Signed-off-by: Keir Fraser <keir.fraser@citrix.com>
Diffstat (limited to 'xen/arch/x86/x86_64/mm.c')
-rw-r--r-- | xen/arch/x86/x86_64/mm.c | 10 |
1 files changed, 8 insertions, 2 deletions
diff --git a/xen/arch/x86/x86_64/mm.c b/xen/arch/x86/x86_64/mm.c index 271cea5ef3..126b2c9421 100644 --- a/xen/arch/x86/x86_64/mm.c +++ b/xen/arch/x86/x86_64/mm.c @@ -163,9 +163,15 @@ void *do_page_walk(struct vcpu *v, unsigned long addr) void __init pfn_pdx_hole_setup(unsigned long mask) { - unsigned int i, j, bottom_shift, hole_shift; + unsigned int i, j, bottom_shift = 0, hole_shift = 0; - for ( hole_shift = bottom_shift = j = 0; ; ) + /* + * We skip the first MAX_ORDER bits, as we never want to compress them. + * This guarantees that page-pointer arithmetic remains valid within + * contiguous aligned ranges of 2^MAX_ORDER pages. Among others, our + * buddy allocator relies on this assumption. + */ + for ( j = MAX_ORDER-1; ; ) { i = find_next_zero_bit(&mask, BITS_PER_LONG, j); j = find_next_bit(&mask, BITS_PER_LONG, i); |