[Xen-devel] [PATCH v3 1/1] xen: move TLB-flush filtering out into populate_physmap during vm creation

[Dongli Zhang <dongli.zhang@xxxxxxxxxx>]

This patch implemented parts of TODO left in commit id
a902c12ee45fc9389eb8fe54eeddaf267a555c58. It moved TLB-flush filtering out
into populate_physmap. Because of TLB-flush in alloc_heap_pages, it's very
slow to create a guest with memory size of more than 100GB on host with
100+ cpus.

This patch introduced a "MEMF_no_tlbflush" bit to memflags to indicate
whether TLB-flush should be done in alloc_heap_pages or its caller
populate_physmap. Once this bit is set in memflags, alloc_heap_pages will
ignore TLB-flush. To use this bit after vm is created might lead to
security issue, that is, this would make pages accessible to the guest B,
when guest A may still have a cached mapping to them.

Therefore, this patch also introduced a "already_scheduled" field to struct
domain to indicate whether this domain has ever got scheduled by
hypervisor.  MEMF_no_tlbflush can be set only during vm creation phase when
already_scheduled is still 0 before this domain gets scheduled for the
first time.

TODO: ballooning very huge amount of memory cannot benefit from this patch
and might still be slow.

Signed-off-by: Dongli Zhang <dongli.zhang@xxxxxxxxxx>

---
Changed since v2:
  * Limit this optimization to domain creation time.

---
 xen/common/domain.c     |  2 ++
 xen/common/memory.c     | 33 +++++++++++++++++++++++++++++++++
 xen/common/page_alloc.c |  3 ++-
 xen/common/schedule.c   |  5 +++++
 xen/include/xen/mm.h    |  2 ++
 xen/include/xen/sched.h |  3 +++
 6 files changed, 47 insertions(+), 1 deletion(-)

diff --git a/xen/common/domain.c b/xen/common/domain.c
index a8804e4..611a471 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -303,6 +303,8 @@ struct domain *domain_create(domid_t domid, unsigned int 
domcr_flags,
     if ( !zalloc_cpumask_var(&d->domain_dirty_cpumask) )
         goto fail;
 
+    d->already_scheduled = 0;
+
     if ( domcr_flags & DOMCRF_hvm )
         d->guest_type = guest_type_hvm;
     else if ( domcr_flags & DOMCRF_pvh )
diff --git a/xen/common/memory.c b/xen/common/memory.c
index f34dd56..3641469 100644
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -141,6 +141,8 @@ static void populate_physmap(struct memop_args *a)
     unsigned int i, j;
     xen_pfn_t gpfn, mfn;
     struct domain *d = a->domain, *curr_d = current->domain;
+    bool_t need_tlbflush = 0;
+    uint32_t tlbflush_timestamp = 0;
 
     if ( !guest_handle_subrange_okay(a->extent_list, a->nr_done,
                                      a->nr_extents-1) )
@@ -150,6 +152,12 @@ static void populate_physmap(struct memop_args *a)
                             max_order(curr_d)) )
         return;
 
+    /* MEMF_no_tlbflush can be set only during vm creation phase when
+     * already_scheduled is still 0 before this domain gets scheduled for
+     * the first time. */
+    if ( d->already_scheduled == 0 )
+        a->memflags |= MEMF_no_tlbflush;
+
     for ( i = a->nr_done; i < a->nr_extents; i++ )
     {
         if ( i != a->nr_done && hypercall_preempt_check() )
@@ -214,6 +222,21 @@ static void populate_physmap(struct memop_args *a)
                     goto out;
                 }
 
+                if ( d->already_scheduled == 0 )
+                {
+                    for ( j = 0; j < (1U << a->extent_order); j++ )
+                    {
+                        if ( page[j].u.free.need_tlbflush &&
+                             (page[j].tlbflush_timestamp <= 
tlbflush_current_time()) &&
+                             (!need_tlbflush ||
+                             (page[j].tlbflush_timestamp > 
tlbflush_timestamp)) )
+                        {
+                            need_tlbflush = 1;
+                            tlbflush_timestamp = page[j].tlbflush_timestamp;
+                        }
+                    }
+                }
+
                 mfn = page_to_mfn(page);
             }
 
@@ -232,6 +255,16 @@ static void populate_physmap(struct memop_args *a)
     }
 
 out:
+    if ( need_tlbflush )
+    {
+        cpumask_t mask = cpu_online_map;
+        tlbflush_filter(mask, tlbflush_timestamp);
+        if ( !cpumask_empty(&mask) )
+        {
+            perfc_incr(need_flush_tlb_flush);
+            flush_tlb_mask(&mask);
+        }
+    }
     a->nr_done = i;
 }
 
diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index 18ff6cf..e0283fc 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -827,7 +827,8 @@ static struct page_info *alloc_heap_pages(
         BUG_ON(pg[i].count_info != PGC_state_free);
         pg[i].count_info = PGC_state_inuse;
 
-        if ( pg[i].u.free.need_tlbflush &&
+        if ( !(memflags & MEMF_no_tlbflush) &&
+             pg[i].u.free.need_tlbflush &&
              (pg[i].tlbflush_timestamp <= tlbflush_current_time()) &&
              (!need_tlbflush ||
               (pg[i].tlbflush_timestamp > tlbflush_timestamp)) )
diff --git a/xen/common/schedule.c b/xen/common/schedule.c
index 32a300f..593541a 100644
--- a/xen/common/schedule.c
+++ b/xen/common/schedule.c
@@ -1376,6 +1376,11 @@ static void schedule(void)
 
     next = next_slice.task;
 
+    /* Set already_scheduled to 1 when this domain gets scheduled for the
+     * first time */
+    if ( next->domain->already_scheduled == 0 )
+        next->domain->already_scheduled = 1;
+
     sd->curr = next;
 
     if ( next_slice.time >= 0 ) /* -ve means no limit */
diff --git a/xen/include/xen/mm.h b/xen/include/xen/mm.h
index 58bc0b8..880ca88 100644
--- a/xen/include/xen/mm.h
+++ b/xen/include/xen/mm.h
@@ -221,6 +221,8 @@ struct npfec {
 #define  MEMF_exact_node  (1U<<_MEMF_exact_node)
 #define _MEMF_no_owner    5
 #define  MEMF_no_owner    (1U<<_MEMF_no_owner)
+#define _MEMF_no_tlbflush 6
+#define  MEMF_no_tlbflush (1U<<_MEMF_no_tlbflush)
 #define _MEMF_node        8
 #define  MEMF_node_mask   ((1U << (8 * sizeof(nodeid_t))) - 1)
 #define  MEMF_node(n)     ((((n) + 1) & MEMF_node_mask) << _MEMF_node)
diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index 2f9c15f..cbd8329 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -474,6 +474,9 @@ struct domain
         unsigned int guest_request_enabled       : 1;
         unsigned int guest_request_sync          : 1;
     } monitor;
+
+    /* set to 1 the first time this domain gets scheduled. */
+    bool_t already_scheduled;
 };
 
 /* Protect updates/reads (resp.) of domain_list and domain_hash. */
-- 
1.9.1


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