46 lines
1.5 KiB
Diff
46 lines
1.5 KiB
Diff
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# HG changeset patch
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# User Keir Fraser <keir.fraser@citrix.com>
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# Date 1283153992 -3600
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# Node ID c5aed2e049bce2724b035dd6aa09c4c4e609c27c
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# Parent 20920c12bc4815b1f755786c0924393809664807
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ept: Put locks around ept_get_entry
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There's a subtle race in ept_get_entry, such that if tries to read an
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entry that ept_set_entry is modifying, it gets neither the old entry
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nor the new entry, but empty. In the case of multi-cpu
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populate-on-demand guests, this manifests as a guest crash when one
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vcpu tries to read a page which another page is trying to populate,
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and ept_get_entry returns p2m_mmio_dm.
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This bug can also be fixed by making both ept_set_entry and
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ept_next_level access-once (i.e., ept_next_level reads full ept_entry
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and then works with local value; ept_set_entry construct the entry
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locally and then sets it in one write). But there doesn't seem to be
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any major performance implications of just making ept_get_entry use
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locks; so the simpler, the better.
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Signed-off-by: George Dunlap <george.dunlap@eu.citrix.com>
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--- a/xen/arch/x86/mm/hap/p2m-ept.c
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+++ b/xen/arch/x86/mm/hap/p2m-ept.c
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@@ -387,6 +387,10 @@ static mfn_t ept_get_entry(struct domain
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int i;
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int ret = 0;
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mfn_t mfn = _mfn(INVALID_MFN);
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+ int do_locking = !p2m_locked_by_me(d->arch.p2m);
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+
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+ if ( do_locking )
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+ p2m_lock(d->arch.p2m);
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*t = p2m_mmio_dm;
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@@ -464,6 +468,8 @@ static mfn_t ept_get_entry(struct domain
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}
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out:
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+ if ( do_locking )
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+ p2m_unlock(d->arch.p2m);
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unmap_domain_page(table);
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return mfn;
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}
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