[Xen-devel] [PATCH v2 1/2] x86/mem-sharing: Bulk mem-sharing entire domains

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

Currently mem-sharing can be performed on a page-by-page base from the control
domain. However, when completely deduplicating (cloning) a VM, this requires
at least 3 hypercalls per page. As the user has to loop through all pages up
to max_gpfn, this process is very slow and wasteful.

This patch introduces a new mem_sharing memop for bulk deduplication where
the user doesn't have to separately nominate each page in both the source and
destination domain, and the looping over all pages happen in the hypervisor.
This significantly reduces the overhead of completely deduplicating entire
domains.

Signed-off-by: Tamas K Lengyel <tlengyel@xxxxxxxxxxx>
Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Cc: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
Cc: Keir Fraser <keir@xxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>
---
v2: Stash hypercall continuation start point in xen_mem_sharing_op_t
    Return number of successfully shared pages in xen_mem_sharing_op_t
---
 tools/libxc/include/xenctrl.h | 13 +++++++
 tools/libxc/xc_memshr.c       | 19 ++++++++++
 xen/arch/x86/mm/mem_sharing.c | 84 +++++++++++++++++++++++++++++++++++++++++++
 xen/include/public/memory.h   |  9 ++++-
 4 files changed, 124 insertions(+), 1 deletion(-)

diff --git a/tools/libxc/include/xenctrl.h b/tools/libxc/include/xenctrl.h
index 3bfa00b..2476ebc 100644
--- a/tools/libxc/include/xenctrl.h
+++ b/tools/libxc/include/xenctrl.h
@@ -2594,6 +2594,19 @@ int xc_memshr_add_to_physmap(xc_interface *xch,
                     domid_t client_domain,
                     unsigned long client_gfn);
 
+/* Allows to deduplicate the entire memory of a client domain in bulk. Using
+ * this function is equivalent of calling xc_memshr_nominate_gfn for each gfn
+ * in the two domains followed by xc_memshr_share_gfns. If successfull,
+ * returns the number of shared pages in 'shared'.
+ *
+ * May fail with -EINVAL if the source and client domain have different
+ * memory size or if memory sharing is not enabled on either of the domains.
+ */
+int xc_memshr_bulk_share(xc_interface *xch,
+                         domid_t source_domain,
+                         domid_t client_domain,
+                         uint64_t *shared);
+
 /* Debug calls: return the number of pages referencing the shared frame backing
  * the input argument. Should be one or greater. 
  *
diff --git a/tools/libxc/xc_memshr.c b/tools/libxc/xc_memshr.c
index deb0aa4..71350d2 100644
--- a/tools/libxc/xc_memshr.c
+++ b/tools/libxc/xc_memshr.c
@@ -181,6 +181,25 @@ int xc_memshr_add_to_physmap(xc_interface *xch,
     return xc_memshr_memop(xch, source_domain, &mso);
 }
 
+int xc_memshr_bulk_share(xc_interface *xch,
+                         domid_t source_domain,
+                         domid_t client_domain,
+                         uint64_t *shared)
+{
+    int rc;
+    xen_mem_sharing_op_t mso;
+
+    memset(&mso, 0, sizeof(mso));
+
+    mso.op = XENMEM_sharing_op_bulk_share;
+    mso.u.bulk.client_domain = client_domain;
+
+    rc = xc_memshr_memop(xch, source_domain, &mso);
+    if ( !rc && shared ) *shared = mso.u.bulk.shared;
+
+    return rc;
+}
+
 int xc_memshr_domain_resume(xc_interface *xch,
                             domid_t domid)
 {
diff --git a/xen/arch/x86/mm/mem_sharing.c b/xen/arch/x86/mm/mem_sharing.c
index a95e105..4cdddb1 100644
--- a/xen/arch/x86/mm/mem_sharing.c
+++ b/xen/arch/x86/mm/mem_sharing.c
@@ -1293,6 +1293,37 @@ int relinquish_shared_pages(struct domain *d)
     return rc;
 }
 
+static int bulk_share(struct domain *d, struct domain *cd, unsigned long max,
+                      struct mem_sharing_op_bulk_share *bulk)
+{
+    int rc = 0;
+    shr_handle_t sh, ch;
+
+    while( bulk->start <= max )
+    {
+        if ( mem_sharing_nominate_page(d, bulk->start, 0, &sh) != 0 )
+            goto next;
+
+        if ( mem_sharing_nominate_page(cd, bulk->start, 0, &ch) != 0 )
+            goto next;
+
+        if ( !mem_sharing_share_pages(d, bulk->start, sh, cd, bulk->start, ch) 
)
+            ++(bulk->shared);
+
+next:
+        ++(bulk->start);
+
+        /* Check for continuation if it's not the last iteration. */
+        if ( bulk->start < max && hypercall_preempt_check() )
+        {
+            rc = 1;
+            break;
+        }
+    }
+
+    return rc;
+}
+
 int mem_sharing_memop(XEN_GUEST_HANDLE_PARAM(xen_mem_sharing_op_t) arg)
 {
     int rc;
@@ -1467,6 +1498,59 @@ int 
mem_sharing_memop(XEN_GUEST_HANDLE_PARAM(xen_mem_sharing_op_t) arg)
         }
         break;
 
+        case XENMEM_sharing_op_bulk_share:
+        {
+            unsigned long max_sgfn, max_cgfn;
+            struct domain *cd;
+
+            rc = -EINVAL;
+            if ( !mem_sharing_enabled(d) )
+                goto out;
+
+            rc = rcu_lock_live_remote_domain_by_id(mso.u.bulk.client_domain,
+                                                   &cd);
+            if ( rc )
+                goto out;
+
+            rc = xsm_mem_sharing_op(XSM_DM_PRIV, d, cd, mso.op);
+            if ( rc )
+            {
+                rcu_unlock_domain(cd);
+                goto out;
+            }
+
+            if ( !mem_sharing_enabled(cd) )
+            {
+                rcu_unlock_domain(cd);
+                rc = -EINVAL;
+                goto out;
+            }
+
+            max_sgfn = domain_get_maximum_gpfn(d);
+            max_cgfn = domain_get_maximum_gpfn(cd);
+
+            if ( max_sgfn != max_cgfn || max_sgfn < mso.u.bulk.start )
+            {
+                rcu_unlock_domain(cd);
+                rc = -EINVAL;
+                goto out;
+            }
+
+            rc = bulk_share(d, cd, max_sgfn, &mso.u.bulk);
+            if ( rc )
+            {
+                if ( __copy_to_guest(arg, &mso, 1) )
+                    rc = -EFAULT;
+                else
+                    rc = hypercall_create_continuation(__HYPERVISOR_memory_op,
+                                                       "lh", XENMEM_sharing_op,
+                                                       arg);
+            }
+
+            rcu_unlock_domain(cd);
+        }
+        break;
+
         case XENMEM_sharing_op_debug_gfn:
         {
             unsigned long gfn = mso.u.debug.u.gfn;
diff --git a/xen/include/public/memory.h b/xen/include/public/memory.h
index 320de91..0299746 100644
--- a/xen/include/public/memory.h
+++ b/xen/include/public/memory.h
@@ -447,6 +447,7 @@ DEFINE_XEN_GUEST_HANDLE(xen_mem_access_op_t);
 #define XENMEM_sharing_op_debug_gref        5
 #define XENMEM_sharing_op_add_physmap       6
 #define XENMEM_sharing_op_audit             7
+#define XENMEM_sharing_op_bulk_share        8
 
 #define XENMEM_SHARING_OP_S_HANDLE_INVALID  (-10)
 #define XENMEM_SHARING_OP_C_HANDLE_INVALID  (-9)
@@ -482,7 +483,13 @@ struct xen_mem_sharing_op {
             uint64_aligned_t client_gfn;    /* IN: the client gfn */
             uint64_aligned_t client_handle; /* IN: handle to the client page */
             domid_t  client_domain; /* IN: the client domain id */
-        } share; 
+        } share;
+        struct mem_sharing_op_bulk_share {   /* OP_BULK_SHARE */
+            domid_t client_domain;           /* IN: the client domain id */
+            uint64_aligned_t start;          /* IN: start gfn (normally 0) */
+            uint64_aligned_t shared;         /* OUT: the number of
+                                                successfully shared pages */
+        } bulk;
         struct mem_sharing_op_debug {     /* OP_DEBUG_xxx */
             union {
                 uint64_aligned_t gfn;      /* IN: gfn to debug          */
-- 
2.1.4


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