58 lines
2.0 KiB
Diff
58 lines
2.0 KiB
Diff
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# Commit b3d2f8b2cba9fce5bc8995612d0d13fcefec7769
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# Date 2014-03-24 10:48:03 +0100
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# Author Jan Beulich <jbeulich@suse.com>
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# Committer Jan Beulich <jbeulich@suse.com>
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x86: fix determination of bit count for struct domain allocations
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We can't just add in the hole shift value, as the hole may be at or
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above the 44-bit boundary. Instead we need to determine the total bit
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count until reaching 32 significant (not squashed out) bits in PFN
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representations.
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Signed-off-by: Jan Beulich <jbeulich@suse.com>
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Acked-by: Keir Fraser <keir@xen.org>
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--- a/xen/arch/x86/domain.c
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+++ b/xen/arch/x86/domain.c
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@@ -180,6 +180,28 @@ void dump_pageframe_info(struct domain *
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spin_unlock(&d->page_alloc_lock);
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}
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+/*
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+ * The hole may be at or above the 44-bit boundary, so we need to determine
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+ * the total bit count until reaching 32 significant (not squashed out) bits
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+ * in PFN representations.
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+ * Note that the way "bits" gets initialized/updated/bounds-checked guarantees
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+ * that the function will never return zero, and hence will never be called
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+ * more than once (which is important due to it being deliberately placed in
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+ * .init.text).
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+ */
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+static unsigned int __init noinline _domain_struct_bits(void)
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+{
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+ unsigned int bits = 32 + PAGE_SHIFT;
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+ unsigned int sig = hweight32(~pfn_hole_mask);
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+ unsigned int mask = pfn_hole_mask >> 32;
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+
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+ for ( ; bits < BITS_PER_LONG && sig < 32; ++bits, mask >>= 1 )
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+ if ( !(mask & 1) )
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+ ++sig;
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+
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+ return bits;
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+}
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+
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struct domain *alloc_domain_struct(void)
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{
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struct domain *d;
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@@ -187,7 +209,10 @@ struct domain *alloc_domain_struct(void)
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* We pack the PDX of the domain structure into a 32-bit field within
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* the page_info structure. Hence the MEMF_bits() restriction.
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*/
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- unsigned int bits = 32 + PAGE_SHIFT + pfn_pdx_hole_shift;
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+ static unsigned int __read_mostly bits;
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+
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+ if ( unlikely(!bits) )
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+ bits = _domain_struct_bits();
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BUILD_BUG_ON(sizeof(*d) > PAGE_SIZE);
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d = alloc_xenheap_pages(0, MEMF_bits(bits));
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