[xen staging] VT-d: free all-empty page tables

[patchbot@xxxxxxx]

commit 00c400edd7f5fed59f109b38522a47cae9943b22
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Mon Jul 25 15:40:41 2022 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Jul 25 15:40:41 2022 +0200

    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@xxxxxxxx>
    Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
    Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Paul Durrant <paul@xxxxxxx>
---
 xen/drivers/passthrough/vtd/iommu.c | 45 +++++++++++++++++++++++++++++++++++--
 1 file changed, 43 insertions(+), 2 deletions(-)

diff --git a/xen/drivers/passthrough/vtd/iommu.c 
b/xen/drivers/passthrough/vtd/iommu.c
index 28dc54b6bf..745c7bae0d 100644
--- 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);
 
--
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