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bitkeeper revision 1.1186 (420cff94zgt9FYAF2LFRO_Xztduveg)
Ensure coherency of guest-PDE 'accessed' bits when using shadow page tables. There is no issue with 'dirty' bits because only PTEs and super-page PDEs (which we do not support) have 'dirty' bits. Signed-off-by: keir.fraser@cl.cam.ac.uk
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@@ -11,12 +11,6 @@
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/********
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To use these shadow page tables, guests must not rely on the ACCESSED
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and DIRTY bits on L2 pte's being accurate -- they will typically all be set.
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I doubt this will break anything. (If guests want to use the va_update
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mechanism they've signed up for this anyhow...)
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There's a per-domain shadow table spin lock which works fine for SMP
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hosts. We don't have to worry about interrupts as no shadow operations
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happen in an interrupt context. It's probably not quite ready for SMP
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@@ -484,8 +478,9 @@ unsigned long shadow_l2_table(
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spl2e = (l2_pgentry_t *)map_domain_mem(spfn << PAGE_SHIFT);
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/*
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* We could proactively fill in PDEs for pages that are already
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* shadowed. However, we tried it and it didn't help performance.
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* This is simpler.
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* shadowed *and* where the guest PDE has _PAGE_ACCESSED set
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* (restriction required for coherence of the accessed bit). However,
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* we tried it and it didn't help performance. This is simpler.
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*/
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memset(spl2e, 0, DOMAIN_ENTRIES_PER_L2_PAGETABLE*sizeof(l2_pgentry_t));
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@@ -498,7 +493,8 @@ unsigned long shadow_l2_table(
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spl2e[SH_LINEAR_PT_VIRT_START >> L2_PAGETABLE_SHIFT] =
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mk_l2_pgentry((spfn << PAGE_SHIFT) | __PAGE_HYPERVISOR);
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spl2e[PERDOMAIN_VIRT_START >> L2_PAGETABLE_SHIFT] =
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mk_l2_pgentry(__pa(page_get_owner(&frame_table[gpfn])->arch.mm_perdomain_pt) |
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mk_l2_pgentry(__pa(page_get_owner(
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&frame_table[gpfn])->arch.mm_perdomain_pt) |
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__PAGE_HYPERVISOR);
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}
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#endif
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@@ -727,7 +723,7 @@ void shadow_l1_normal_pt_update(
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void shadow_l2_normal_pt_update(unsigned long pa, unsigned long gpde)
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{
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unsigned long sl2mfn, spde;
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unsigned long sl2mfn, spde = 0;
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l2_pgentry_t *spl2e;
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unsigned long sl1mfn;
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@@ -736,11 +732,17 @@ void shadow_l2_normal_pt_update(unsigned long pa, unsigned long gpde)
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sl2mfn = __shadow_status(current->domain, pa >> PAGE_SHIFT) & PSH_pfn_mask;
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sl1mfn = (gpde & _PAGE_PRESENT) ?
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__shadow_status(current->domain, gpde >> PAGE_SHIFT) : 0;
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/*
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* Only propagate to shadow if _PAGE_ACCESSED is set in the guest.
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* Otherwise, to ensure coherency, we blow away the existing shadow value.
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*/
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if ( gpde & _PAGE_ACCESSED )
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{
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sl1mfn = (gpde & _PAGE_PRESENT) ?
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__shadow_status(current->domain, gpde >> PAGE_SHIFT) : 0;
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l2pde_general(current->domain, &gpde, &spde, sl1mfn);
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}
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/* XXXX Should mark guest pte as DIRTY and ACCESSED too! */
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l2pde_general(current->domain, &gpde, &spde, sl1mfn);
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spl2e = (l2_pgentry_t *)map_domain_mem(sl2mfn << PAGE_SHIFT);
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spl2e[(pa & ~PAGE_MASK) / sizeof(l2_pgentry_t)] = mk_l2_pgentry(spde);
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unmap_domain_mem(spl2e);
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@@ -331,7 +331,7 @@ static inline void l2pde_general(
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{
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spde = (gpde & ~PAGE_MASK) | (sl1mfn << PAGE_SHIFT) |
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_PAGE_RW | _PAGE_ACCESSED | _PAGE_DIRTY;
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gpde |= _PAGE_ACCESSED | _PAGE_DIRTY;
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gpde |= _PAGE_ACCESSED; /* N.B. PDEs do not have a dirty bit. */
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/* Detect linear p.t. mappings and write-protect them. */
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if ( (frame_table[sl1mfn].u.inuse.type_info & PGT_type_mask) ==
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