x86: adjust available memory calculation for Dom0 construction

With a large number of CPUs, the amount of memory needed to construct
the vCPU structures for Dom0 becomes significant and hence should be
accounted for when calculating the amount of memory to pass to Dom0.

Signed-off-by: Jan Beulich <jbeulich@novell.com>

Add code comments and clean up compute_dom0_nr_pages() invocation.

Signed-off-by: Keir Fraser <keir.fraser@citrix.com>

1 files changed, 18 insertions, 20 deletions

diff --git a/xen/arch/x86/domain_build.c b/xen/arch/x86/domain_build.c
index 8f69aab2a9..498726719f 100644
--- a/xen/arch/x86/domain_build.c
+++ b/xen/arch/x86/domain_build.c
@@ -143,17 +143,20 @@ static struct page_info * __init alloc_chunk(
 }
 
 static unsigned long __init compute_dom0_nr_pages(
-#ifdef __x86_64__
-    unsigned long vstart, unsigned long vend, size_t sizeof_long)
-#else
-    void)
-#endif
+    struct domain *d, struct elf_dom_parms *parms, unsigned long initrd_len)
 {
     unsigned long avail = avail_domheap_pages() + initial_images_nrpages();
     unsigned long nr_pages = dom0_nrpages;
     unsigned long min_pages = dom0_min_nrpages;
     unsigned long max_pages = dom0_max_nrpages;
 
+    /* Reserve memory for further dom0 vcpu-struct allocations... */
+    avail -= (opt_dom0_max_vcpus - 1UL)
+             << get_order_from_bytes(sizeof(struct vcpu));
+    /* ...and compat_l4's, if needed. */
+    if ( is_pv_32on64_domain(d) )
+        avail -= opt_dom0_max_vcpus - 1;
+
     /*
      * If domain 0 allocation isn't specified, reserve 1/16th of available
      * memory for things like DMA buffers. This reservation is clamped to 
@@ -173,8 +176,8 @@ static unsigned long __init compute_dom0_nr_pages(
     nr_pages = min(nr_pages, avail);
 
 #ifdef __x86_64__
-    if ( vstart && dom0_nrpages <= 0 &&
-         (dom0_min_nrpages <= 0 || nr_pages > min_pages) )
+    if ( (parms->p2m_base == UNSET_ADDR) && (dom0_nrpages <= 0) &&
+         ((dom0_min_nrpages <= 0) || (nr_pages > min_pages)) )
     {
         /*
          * Legacy Linux kernels (i.e. such without a XEN_ELFNOTE_INIT_P2M
@@ -184,7 +187,12 @@ static unsigned long __init compute_dom0_nr_pages(
          * allocation doesn't consume more than about half the space that's
          * available between params.virt_base and the address space end.
          */
-        unsigned long end = vend + nr_pages * sizeof_long;
+        unsigned long vstart, vend, end;
+        size_t sizeof_long = is_pv_32bit_domain(d) ? sizeof(int) : sizeof(long);
+
+        vstart = parms->virt_base;
+        vend = round_pgup(parms->virt_kend) + round_pgup(initrd_len);
+        end = vend + nr_pages * sizeof_long;
 
         if ( end > vstart )
             end += end - vstart;
@@ -367,21 +375,11 @@ int __init construct_dom0(
     {
         d->arch.is_32bit_pv = d->arch.has_32bit_shinfo = 1;
         v->vcpu_info = (void *)&d->shared_info->compat.vcpu_info[0];
-
-        nr_pages = compute_dom0_nr_pages(parms.virt_base,
-            round_pgup(parms.virt_kend) + round_pgup(initrd_len),
-            sizeof(unsigned int));
     }
-    else if (parms.p2m_base != UNSET_ADDR)
-        nr_pages = compute_dom0_nr_pages(0, 0, 0);
-    else
-        nr_pages = compute_dom0_nr_pages(parms.virt_base,
-            round_pgup(parms.virt_kend) + round_pgup(initrd_len),
-            sizeof(unsigned long));
-#else
-    nr_pages = compute_dom0_nr_pages();
 #endif
 
+    nr_pages = compute_dom0_nr_pages(d, &parms, initrd_len);
+
     if ( parms.pae == PAEKERN_extended_cr3 )
             set_bit(VMASST_TYPE_pae_extended_cr3, &d->vm_assist);