[Xen-devel] [PATCH v5 3/8] tools: arm: allocate large pages 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>
Acked-by: Julien Grall <julien.grall@xxxxxxxxxx>
Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
---
v4: fixed the code which was supposed to try and realign things to the next
    superpage.
    constify some values
v3: Drop outdated paragraph from commit message
v2: min_t defintion moved into earlier patch
    drop debug_iters
    allocate extents array explicitly instead of putting 8M on the stack.
    Handle OOM, xc_populate_physmap returns 0, which needs handling for L3.
---
 tools/libxc/xc_dom_arm.c |  131 +++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 117 insertions(+), 14 deletions(-)

diff --git a/tools/libxc/xc_dom_arm.c b/tools/libxc/xc_dom_arm.c
index 10f6bcb..9b31b1f 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 +256,72 @@ static int set_mode(xc_interface *xch, domid_t domid, 
char *guest_type)
     return rc;
 }
 
+/*  >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,
+                             xen_pfn_t *extents)
+{
+    /* The mask for this level */
+    const uint64_t mask = ((uint64_t)1<<(pfn_shift))-1;
+    /* The shift, mask and next boundary for the level above this one */
+    const int next_shift = pfn_shift + LPAE_SHIFT;
+    const uint64_t next_mask = ((uint64_t)1<<next_shift)-1;
+    const xen_pfn_t next_boundary
+        = (base_pfn + ((uint64_t)1<<next_shift)) & ~next_mask;
+
+    int nr, i, count;
+    xen_pfn_t end_pfn = base_pfn + *nr_pfns;
+
+    /* No level zero super pages with current hardware */
+    if ( pfn_shift == PFN_512G_SHIFT )
+        return 0;
+
+    /* base is misaligned for this level */
+    if ( mask & base_pfn )
+        return 0;
+
+    /*
+     * If base is not aligned at the next level up then try and make
+     * it so for next time around.
+     */
+    if ( (base_pfn & next_mask) && end_pfn > next_boundary )
+        end_pfn = next_boundary;
+
+    count = ( end_pfn - base_pfn ) >> pfn_shift;
+
+    /* Nothing to allocate */
+    if ( !count )
+        return 0;
+
+    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;
-    xen_pfn_t allocsz, pfn;
+    int rc = 0;
+    xen_pfn_t allocsz, pfn, *extents;
+
+    extents = calloc(1024*1024,sizeof(xen_pfn_t));
+    if ( extents == NULL )
+    {
+        DOMPRINTF("%s: Unable to allocate extent array", __FUNCTION__);
+        return -1;
+    }
 
     DOMPRINTF("%s: populating RAM @ %016"PRIx64"-%016"PRIx64" (%"PRId64"MB)",
               __FUNCTION__,
@@ -261,21 +329,56 @@ 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]);
+        allocsz = min_t(int, 1024*1024, nr_pfns - pfn);
+#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, extents);
+            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, extents);
+        if ( rc < 0 ) break;
+        if ( rc > 0 ) continue;
+
+        rc = populate_one_size(dom, PFN_1G_SHIFT,
+                               base_pfn + pfn, &allocsz, extents);
+        if ( rc < 0 ) break;
+        if ( rc > 0 ) continue;
+
+        rc = populate_one_size(dom, PFN_2M_SHIFT,
+                               base_pfn + pfn, &allocsz, extents);
+        if ( rc < 0 ) break;
+        if ( rc > 0 ) continue;
+
+        rc = populate_one_size(dom, PFN_4K_SHIFT,
+                               base_pfn + pfn, &allocsz, extents);
+        if ( rc < 0 ) break;
+        if ( rc == 0 )
+        {
+            DOMPRINTF("%s: Not enough RAM", __FUNCTION__);
+            errno = ENOMEM;
+            rc = -1;
+            goto out;
+        }
     }
 
-    return rc;
+    for ( pfn = 0; pfn < nr_pfns; pfn++ )
+        dom->p2m_host[pfn] = base_pfn + pfn;
+
+out:
+    free(extents);
+    return rc < 0 ? rc : 0;
 }
 
 int arch_setup_meminit(struct xc_dom_image *dom)
-- 
1.7.10.4


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