[Xen-devel] [PATCH] x86/pvh: fix memory accounting for Dom0

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

Make sure that the memory for the paging structures in case of a HVM
Dom0 is subtracted from the total amount of memory available for Dom0
to use. Also take into account whether the IOMMU is sharing the
page tables with HAP, or else also reserve some memory for the IOMMU
page tables.

While there re-organize the code slightly so that the for loop and the
need_paging local variable can be removed.

Reported-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
I've tested booting a PVHv2 Dom0 without dom0_mem set (and
with/without no-sharept), and it works fine. Current code doesn't work
if dom0_mem is not set to a reasonable value.
---
 xen/arch/x86/dom0_build.c | 51 +++++++++++++++++++++++------------------------
 1 file changed, 25 insertions(+), 26 deletions(-)

diff --git a/xen/arch/x86/dom0_build.c b/xen/arch/x86/dom0_build.c
index f616b99ddc..3a9aac8aca 100644
--- a/xen/arch/x86/dom0_build.c
+++ b/xen/arch/x86/dom0_build.c
@@ -241,7 +241,6 @@ unsigned long __init dom0_compute_nr_pages(
 {
     nodeid_t node;
     unsigned long avail = 0, nr_pages, min_pages, max_pages;
-    bool need_paging;
 
     for_each_node_mask ( node, dom0_nodes )
         avail += avail_domheap_pages_region(node, 0, 0) +
@@ -263,39 +262,39 @@ unsigned long __init dom0_compute_nr_pages(
             avail -= max_pdx >> s;
     }
 
-    need_paging = is_hvm_domain(d) &&
-        (!iommu_hap_pt_share || !paging_mode_hap(d));
-    for ( ; ; need_paging = false )
-    {
-        nr_pages = dom0_nrpages;
-        min_pages = dom0_min_nrpages;
-        max_pages = dom0_max_nrpages;
+    nr_pages = dom0_nrpages;
+    min_pages = dom0_min_nrpages;
+    max_pages = dom0_max_nrpages;
 
-        /*
-         * If allocation isn't specified, reserve 1/16th of available memory
-         * for things like DMA buffers. This reservation is clamped to a
-         * maximum of 128MB.
-         */
-        if ( nr_pages == 0 )
-            nr_pages = -min(avail / 16, 128UL << (20 - PAGE_SHIFT));
+    /*
+     * If allocation isn't specified, reserve 1/16th of available memory
+     * for things like DMA buffers. This reservation is clamped to a
+     * maximum of 128MB.
+     */
+    if ( nr_pages == 0 )
+        nr_pages = -min(avail / 16, 128UL << (20 - PAGE_SHIFT));
 
-        /* Negative specification means "all memory - specified amount". */
-        if ( (long)nr_pages  < 0 ) nr_pages  += avail;
-        if ( (long)min_pages < 0 ) min_pages += avail;
-        if ( (long)max_pages < 0 ) max_pages += avail;
+    /* Negative specification means "all memory - specified amount". */
+    if ( (long)nr_pages  < 0 ) nr_pages  += avail;
+    if ( (long)min_pages < 0 ) min_pages += avail;
+    if ( (long)max_pages < 0 ) max_pages += avail;
 
-        /* Clamp according to min/max limits and available memory. */
-        nr_pages = max(nr_pages, min_pages);
-        nr_pages = min(nr_pages, max_pages);
-        nr_pages = min(nr_pages, avail);
+    /* Clamp according to min/max limits and available memory. */
+    nr_pages = max(nr_pages, min_pages);
+    nr_pages = min(nr_pages, max_pages);
 
-        if ( !need_paging )
-            break;
+    if ( is_hvm_domain(d) )
+    {
+        unsigned long paging_mem = dom0_paging_pages(d, nr_pages);
 
         /* Reserve memory for shadow or HAP. */
-        avail -= dom0_paging_pages(d, nr_pages);
+        avail -= paging_mem;
+        /* Reserve the same amount for the IOMMU page tables if not shared. */
+        avail -= !iommu_hap_pt_share ? paging_mem : 0;
     }
 
+    nr_pages = min(nr_pages, avail);
+
     if ( is_pv_domain(d) &&
          (parms->p2m_base == UNSET_ADDR) && (dom0_nrpages <= 0) &&
          ((dom0_min_nrpages <= 0) || (nr_pages > min_pages)) )
-- 
2.13.5 (Apple Git-94)


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