VT-d: free all-empty page tables

When a page table ends up with no present entries left, it can be
replaced by a non-present entry at the next higher level. The page table
itself can then be scheduled for freeing.

Note that while its output isn't used there yet,
pt_update_contig_markers() right away needs to be called in all places
where entries get updated, not just the one where entries get cleared.

Note further that while pt_update_contig_markers() updates perhaps
several PTEs within the table, since these are changes to "avail" bits
only I do not think that cache flushing would be needed afterwards. Such
cache flushing (of entire pages, unless adding yet more logic to me more
selective) would be quite noticable performance-wise (very prominent
during Dom0 boot).

Also note that cache sync-ing is likely more strict than necessary. This
is both to be on the safe side as well as to maintain the pattern of all
updates of (potentially) live tables being accompanied by a flush (if so
needed).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Paul Durrant <paul@xen.org>

diff --git a/xen/drivers/passthrough/vtd/iommu.c b/xen/drivers/passthrough/vtd/iommu.c
index 28dc54b6bfb4b826796c4388a900654a03d2b0f9..745c7bae0dec426ff87633d3a9fd82ef84d577fa 100644 (file)
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -43,6 +43,9 @@
 #include "vtd.h"
 #include "../ats.h"
 
+#define CONTIG_MASK DMA_PTE_CONTIG_MASK
+#include <asm/pt-contig-markers.h>
+
 /* dom_io is used as a sentinel for quarantined devices */
 #define QUARANTINE_SKIP(d, pgd_maddr) ((d) == dom_io && !(pgd_maddr))
 #define DEVICE_DOMID(d, pdev) ((d) != dom_io ? (d)->domain_id \
@@ -405,6 +408,9 @@ static uint64_t addr_to_dma_page_maddr(struct domain *domain, daddr_t addr,
 
             write_atomic(&pte->val, new_pte.val);
             iommu_sync_cache(pte, sizeof(struct dma_pte));
+            pt_update_contig_markers(&parent->val,
+                                     address_level_offset(addr, level),
+                                     level, PTE_kind_table);
         }
 
         if ( --level == target )
@@ -829,9 +835,31 @@ static int dma_pte_clear_one(struct domain *domain, daddr_t addr,
 
     old = *pte;
     dma_clear_pte(*pte);
+    iommu_sync_cache(pte, sizeof(*pte));
+
+    while ( pt_update_contig_markers(&page->val,
+                                     address_level_offset(addr, level),
+                                     level, PTE_kind_null) &&
+            ++level < min_pt_levels )
+    {
+        struct page_info *pg = maddr_to_page(pg_maddr);
+
+        unmap_vtd_domain_page(page);
+
+        pg_maddr = addr_to_dma_page_maddr(domain, addr, level, flush_flags,
+                                          false);
+        BUG_ON(pg_maddr < PAGE_SIZE);
+
+        page = map_vtd_domain_page(pg_maddr);
+        pte = &page[address_level_offset(addr, level)];
+        dma_clear_pte(*pte);
+        iommu_sync_cache(pte, sizeof(*pte));
+
+        *flush_flags |= IOMMU_FLUSHF_all;
+        iommu_queue_free_pgtable(hd, pg);
+    }
 
     spin_unlock(&hd->arch.mapping_lock);
-    iommu_sync_cache(pte, sizeof(struct dma_pte));
 
     unmap_vtd_domain_page(page);
 
@@ -2177,8 +2205,21 @@ static int __must_check cf_check intel_iommu_map_page(
     }
 
     *pte = new;
-
     iommu_sync_cache(pte, sizeof(struct dma_pte));
+
+    /*
+     * While the (ab)use of PTE_kind_table here allows to save some work in
+     * the function, the main motivation for it is that it avoids a so far
+     * unexplained hang during boot (while preparing Dom0) on a Westmere
+     * based laptop.
+     */
+    pt_update_contig_markers(&page->val,
+                             address_level_offset(dfn_to_daddr(dfn), level),
+                             level,
+                             (hd->platform_ops->page_sizes &
+                              (1UL << level_to_offset_bits(level + 1))
+                              ? PTE_kind_leaf : PTE_kind_table));
+
     spin_unlock(&hd->arch.mapping_lock);
     unmap_vtd_domain_page(page);