124 lines
4.4 KiB
Diff
124 lines
4.4 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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@@ -137,7 +137,7 @@ static int ept_next_level(struct domain
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ept_entry_t **table, unsigned long *gfn_remainder,
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u32 shift)
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{
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- ept_entry_t *ept_entry;
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+ ept_entry_t *ept_entry, e;
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ept_entry_t *next;
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u32 index;
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@@ -145,9 +145,11 @@ static int ept_next_level(struct domain
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ept_entry = (*table) + index;
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- if ( !is_epte_present(ept_entry) )
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+ e=*ept_entry;
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+
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+ if ( !is_epte_present(&e) )
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{
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- if ( ept_entry->avail1 == p2m_populate_on_demand )
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+ if ( e.avail1 == p2m_populate_on_demand )
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return GUEST_TABLE_POD_PAGE;
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if ( read_only )
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@@ -155,15 +157,17 @@ static int ept_next_level(struct domain
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if ( !ept_set_middle_entry(d, ept_entry) )
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return GUEST_TABLE_MAP_FAILED;
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+ else
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+ e=*ept_entry;
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}
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/* The only time sp would be set here is if we had hit a superpage */
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- if ( is_epte_superpage(ept_entry) )
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+ if ( is_epte_superpage(&e) )
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return GUEST_TABLE_SUPER_PAGE;
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else
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{
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*gfn_remainder &= (1UL << shift) - 1;
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- next = map_domain_page(ept_entry->mfn);
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+ next = map_domain_page(e.mfn);
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unmap_domain_page(*table);
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*table = next;
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return GUEST_TABLE_NORMAL_PAGE;
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@@ -235,35 +239,39 @@ ept_set_entry(struct domain *d, unsigned
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if ( mfn_valid(mfn_x(mfn)) || direct_mmio || p2m_is_paged(p2mt) ||
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(p2mt == p2m_ram_paging_in_start) )
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{
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- ept_entry->emt = epte_get_entry_emt(d, gfn, mfn, &ipat,
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+ ept_entry_t new_entry;
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+
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+ new_entry.emt = epte_get_entry_emt(d, gfn, mfn, &ipat,
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direct_mmio);
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- ept_entry->ipat = ipat;
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- ept_entry->sp = order ? 1 : 0;
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+ new_entry.ipat = ipat;
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+ new_entry.sp = order ? 1 : 0;
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if ( ret == GUEST_TABLE_SUPER_PAGE )
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{
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- if ( ept_entry->mfn == (mfn_x(mfn) - offset) )
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+ if ( new_entry.mfn == (mfn_x(mfn) - offset) )
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need_modify_vtd_table = 0;
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else
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- ept_entry->mfn = mfn_x(mfn) - offset;
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+ new_entry.mfn = mfn_x(mfn) - offset;
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- if ( (ept_entry->avail1 == p2m_ram_logdirty)
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+ if ( (new_entry.avail1 == p2m_ram_logdirty)
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&& (p2mt == p2m_ram_rw) )
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for ( i = 0; i < 512; i++ )
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paging_mark_dirty(d, mfn_x(mfn) - offset + i);
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}
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else
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{
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- if ( ept_entry->mfn == mfn_x(mfn) )
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+ if ( new_entry.mfn == mfn_x(mfn) )
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need_modify_vtd_table = 0;
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else
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- ept_entry->mfn = mfn_x(mfn);
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+ new_entry.mfn = mfn_x(mfn);
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}
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- ept_entry->avail1 = p2mt;
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- ept_entry->avail2 = 0;
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+ new_entry.avail1 = p2mt;
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+ new_entry.avail2 = 0;
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+
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+ ept_p2m_type_to_flags(&new_entry, p2mt);
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- ept_p2m_type_to_flags(ept_entry, p2mt);
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+ ept_entry->epte = new_entry.epte;
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}
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else
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ept_entry->epte = 0;
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