[Xen-devel] [PATCH 2/6] tools: arm: allocate superpages to guests.

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

Tries to allocate as many large (1G or 2M) pages as it can to the guest and 
tries
to align to the next larger size on each attempt so that we can attempt to
allocate even larger pages on the next iteration (this is currently only
exercised via a compile time debug option, which is left in place under a #if
0).

Since ARM page tables are consistent at each level there is a common helper
function which tries to allocate a levels worth of pages. The exception to this
consistency is level 0 which does not support table mappings (0.5TB
superpages!).

Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
---
 tools/libxc/xc_dom_arm.c |  103 +++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 92 insertions(+), 11 deletions(-)

diff --git a/tools/libxc/xc_dom_arm.c b/tools/libxc/xc_dom_arm.c
index 75f8363..da68ec3 100644
--- a/tools/libxc/xc_dom_arm.c
+++ b/tools/libxc/xc_dom_arm.c
@@ -30,6 +30,13 @@
 #define CONSOLE_PFN_OFFSET 0
 #define XENSTORE_PFN_OFFSET 1
 
+#define LPAE_SHIFT 9
+
+#define PFN_4K_SHIFT  (0)
+#define PFN_2M_SHIFT  (PFN_4K_SHIFT+LPAE_SHIFT)
+#define PFN_1G_SHIFT  (PFN_2M_SHIFT+LPAE_SHIFT)
+#define PFN_512G_SHIFT (PFN_1G_SHIFT+LPAE_SHIFT)
+
 /* get guest IO ABI protocol */
 const char *xc_domain_get_native_protocol(xc_interface *xch,
                                           uint32_t domid)
@@ -249,11 +256,57 @@ static int set_mode(xc_interface *xch, domid_t domid, 
char *guest_type)
     return rc;
 }
 
+#define min_t(type,x,y) \
+        ({ type __x = (x); type __y = (y); __x < __y ? __x: __y; })
+
+/*  >0: success, *nr_pfns set to number actually populated
+ *   0: didn't try with this pfn shift (e.g. misaligned base etc)
+ *  <0: ERROR
+ */
+static int populate_one_size(struct xc_dom_image *dom, int pfn_shift,
+                             xen_pfn_t base_pfn, xen_pfn_t *nr_pfns)
+{
+    uint64_t mask = ((uint64_t)1<<(pfn_shift))-1;
+    uint64_t next_mask = ((uint64_t)1<<(LPAE_SHIFT))-1;
+    int nr, i, count = min_t(int, 1024*1024, *nr_pfns >> pfn_shift);
+    xen_pfn_t extents[count];
+
+    /* No level zero super pages with current hardware */
+    if ( pfn_shift == PFN_512G_SHIFT )
+        return 0;
+
+    /* Nothing to allocate */
+    if ( !count )
+        return 0;
+
+    /* base is misaligned for this level */
+    if ( mask & base_pfn )
+        return 0;
+
+    /* align to the end of a super page at this level */
+    if ( count & next_mask )
+        count &= next_mask;
+
+    for ( i = 0 ; i < count ; i ++ )
+        extents[i] = base_pfn + (i<<pfn_shift);
+
+    nr = xc_domain_populate_physmap(dom->xch, dom->guest_domid, count,
+                                    pfn_shift, 0, extents);
+    if ( nr <= 0 ) return nr;
+    DOMPRINTF("%s: populated %#x/%#x entries with shift %d",
+              __FUNCTION__, nr, count, pfn_shift);
+
+    *nr_pfns = nr << pfn_shift;
+
+    return 1;
+}
+
 static int populate_guest_memory(struct xc_dom_image *dom,
                                  xen_pfn_t base_pfn, xen_pfn_t nr_pfns)
 {
-    int rc;
+    int rc = 0;
     xen_pfn_t allocsz, pfn;
+    int debug_iters = 0;
 
     DOMPRINTF("%s: populating RAM @ %016"PRIx64"-%016"PRIx64" (%"PRId64"MB)",
               __FUNCTION__,
@@ -261,21 +314,49 @@ static int populate_guest_memory(struct xc_dom_image *dom,
               (uint64_t)(base_pfn + nr_pfns) << XC_PAGE_SHIFT,
               (uint64_t)nr_pfns >> (20-XC_PAGE_SHIFT));
 
-    for ( pfn = 0; pfn < nr_pfns; pfn++ )
-        dom->p2m_host[pfn] = base_pfn + pfn;
-
-    for ( pfn = rc = allocsz = 0; (pfn < nr_pfns) && !rc; pfn += allocsz )
+    for ( pfn = 0; pfn < nr_pfns; pfn += allocsz )
     {
         allocsz = nr_pfns - pfn;
-        if ( allocsz > 1024*1024 )
-            allocsz = 1024*1024;
 
-        rc = xc_domain_populate_physmap_exact(
-            dom->xch, dom->guest_domid, allocsz,
-            0, 0, &dom->p2m_host[pfn]);
+        if ( debug_iters++ > 4 )
+            abort();
+#if 0 /* Enable this to exercise/debug the code which tries to realign
+       * to a superpage boundary, by misaligning at the start. */
+        if ( pfn == 0 )
+        {
+            allocsz = 1;
+            rc = populate_one_size(dom, PFN_4K_SHIFT, base_pfn + pfn, 
&allocsz);
+            if (rc < 0) break;
+            if (rc > 0) continue;
+            /* Failed to allocate a single page? */
+            break;
+        }
+#endif
+
+        rc = populate_one_size(dom, PFN_512G_SHIFT, base_pfn + pfn, &allocsz);
+        if (rc < 0) break;
+        if (rc > 0) continue;
+
+        rc = populate_one_size(dom, PFN_1G_SHIFT, base_pfn + pfn, &allocsz);
+        if (rc < 0) break;
+        if (rc > 0) continue;
+
+        rc = populate_one_size(dom, PFN_2M_SHIFT, base_pfn + pfn, &allocsz);
+        if (rc < 0) break;
+        if (rc > 0) continue;
+
+        rc = populate_one_size(dom, PFN_4K_SHIFT, base_pfn + pfn, &allocsz);
+        if (rc < 0) break;
+
+        assert(rc > 0); /* Must have tried to allocate some 4k pages! */
     }
 
-    return rc;
+    DOMPRINTF("%s: rc=%d", __FUNCTION__, rc);
+
+    for ( pfn = 0; pfn < nr_pfns; pfn++ )
+        dom->p2m_host[pfn] = base_pfn + pfn;
+
+    return rc < 0 ? rc : 0;
 }
 
 int arch_setup_meminit(struct xc_dom_image *dom)
-- 
1.7.10.4


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