[Xen-devel] [PATCH 2/2] x86/dom0: improve paging memory usage calculations

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

Current approximation of paging memory usage is based on the required
amount when running in shadow mode and doesn't take into account the
memory required by the IOMMU page tables.

Fix this by introducing a function to calculate the amount of memory
required by HAP/IOMMU page tables. The formula used to calculate such
approximation is based on the pessimistic approach that each 4KB
memory chunk will use 8 bytes of page table memory. Hopefully this will
leave plenty of room in order to map MMIO regions which are not taken
into account. Note that this approximation might need further tuning
based on testing on different systems.

Also fix the calculation of the required paging related memory in
dom0_compute_nr_pages to take into account the paging implementation
(shadow or HAP) and whether the IOMMU pages tables are shared with the
HAP page tables.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
Cc: andrei.semenov@xxxxxxxxx
---
 xen/arch/x86/dom0_build.c        | 25 +++++++++++++++++++++----
 xen/arch/x86/hvm/dom0_build.c    |  6 ++++--
 xen/include/asm-x86/dom0_build.h |  2 ++
 3 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/xen/arch/x86/dom0_build.c b/xen/arch/x86/dom0_build.c
index ba9aa85611..475a170c95 100644
--- a/xen/arch/x86/dom0_build.c
+++ b/xen/arch/x86/dom0_build.c
@@ -267,6 +267,19 @@ unsigned long __init dom0_shadow_pages(const struct domain 
*d,
     return ((memkb + 1023) / 1024) << (20 - PAGE_SHIFT);
 }
 
+unsigned long __init dom0_hap_pages(const struct domain *d,
+                                    unsigned long nr_pages)
+{
+    /*
+     * Approximate the memory required for the HAP/IOMMU page tables by
+     * pessimistically assuming each 4KB page will consume a 8 byte page
+     * table entry. This should hopefully cover up for MMIO mappings not
+     * accounted here.
+     */
+    return DIV_ROUND_UP(nr_pages * 8, PAGE_SIZE << PAGE_ORDER_4K);
+}
+
+
 unsigned long __init dom0_compute_nr_pages(
     struct domain *d, struct elf_dom_parms *parms, unsigned long initrd_len)
 {
@@ -294,8 +307,7 @@ 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));
+    need_paging = is_hvm_domain(d);
     for ( ; ; need_paging = false )
     {
         nr_pages = dom0_nrpages;
@@ -324,8 +336,13 @@ unsigned long __init dom0_compute_nr_pages(
         if ( !need_paging )
             break;
 
-        /* Reserve memory for shadow or HAP. */
-        avail -= dom0_shadow_pages(d, nr_pages);
+        /* Reserve memory for CPU and IOMMU page tables. */
+        if ( paging_mode_hap(d) )
+            avail -= dom0_hap_pages(d, nr_pages) *
+                     (iommu_hap_pt_share ? 1 : 2);
+        else
+            avail -= dom0_shadow_pages(d, nr_pages) +
+                     dom0_hap_pages(d, nr_pages);
     }
 
     if ( is_pv_domain(d) &&
diff --git a/xen/arch/x86/hvm/dom0_build.c b/xen/arch/x86/hvm/dom0_build.c
index 2af2bd8c3d..7217b2404a 100644
--- a/xen/arch/x86/hvm/dom0_build.c
+++ b/xen/arch/x86/hvm/dom0_build.c
@@ -358,6 +358,9 @@ static int __init pvh_setup_p2m(struct domain *d)
 {
     struct vcpu *v = d->vcpu[0];
     unsigned long nr_pages = dom0_compute_nr_pages(d, NULL, 0);
+    unsigned long paging_pages =
+        paging_mode_hap(d) ? dom0_hap_pages(d, nr_pages),
+                           : dom0_shadow_pages(d, nr_pages);
     unsigned int i;
     int rc;
     bool preempted;
@@ -366,8 +369,7 @@ static int __init pvh_setup_p2m(struct domain *d)
     pvh_setup_e820(d, nr_pages);
     do {
         preempted = false;
-        paging_set_allocation(d, dom0_shadow_pages(d, nr_pages),
-                              &preempted);
+        paging_set_allocation(d, paging_pages, &preempted);
         process_pending_softirqs();
     } while ( preempted );
 
diff --git a/xen/include/asm-x86/dom0_build.h b/xen/include/asm-x86/dom0_build.h
index 22f960b8b0..e1309c25e8 100644
--- a/xen/include/asm-x86/dom0_build.h
+++ b/xen/include/asm-x86/dom0_build.h
@@ -27,6 +27,8 @@ int dom0_construct_pvh(struct domain *d, const module_t 
*image,
 
 unsigned long dom0_shadow_pages(const struct domain *d,
                                 unsigned long nr_pages);
+unsigned long dom0_hap_pages(const struct domain *d,
+                             unsigned long nr_pages);
 
 void dom0_update_physmap(struct domain *d, unsigned long pfn,
                          unsigned long mfn, unsigned long vphysmap_s);
-- 
2.19.1


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