50 lines
1.6 KiB
Diff
50 lines
1.6 KiB
Diff
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# HG changeset patch
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# User Keir Fraser <keir@xen.org>
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# Date 1292410025 0
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# Node ID 7a5ee380041707177ca9c78e800095d1f5f3d373
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# Parent 01f3b350902385627d1fa9e8cd1c231953e7610c
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ept: Remove lock in ept_get_entry, replace with access-once semantics.
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This mirrors the RVI/shadow situation, where p2m read access is
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lockless because it's done in the hardware (linear map of the p2m
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table).
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This fixes the original bug (call it bug A) without introducing bug B
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(a deadlock).
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Bug A was caused by a race when updating p2m entries: between testing
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if it's valid, and testing if it's populate-on-demand, it may have
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been changed from populate-on-demand to valid.
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My original patch simply introduced a lock into ept_get_entry, but
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that caused bug B, caused by circular locking order: p2m_change_type
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[grabs p2m lock] -> set_p2m_entry -> ept_set_entry ->
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ept_set_middle_level -> p2m_alloc [grabs hap lock] write cr4 ->
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hap_update_paging_modes [grabes hap lock] -> hap_update_cr3 ->
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gfn_to_mfn -> ept_get_entry -> [grabs p2m lock]
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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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@@ -395,10 +395,6 @@ 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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@@ -476,8 +472,6 @@ 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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