[Xen-changelog] [xen master] x86: correct vCPU dirty CPU handling

[patchbot@xxxxxxx]

commit 607ce6507dbb936048a702bd930a39ed6bb8ae1a
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Tue May 22 16:00:32 2018 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue May 22 16:00:32 2018 +0200

    x86: correct vCPU dirty CPU handling
    
    Commit df8234fd2c ("replace vCPU's dirty CPU mask by numeric ID") was
    too lax in two respects: First of all it didn't consider the case of a
    vCPU not having a valid dirty CPU in the descriptor table TLB flush
    case. This is the issue Manual has run into with NetBSD.
    
    Additionally reads of ->dirty_cpu for other than the current vCPU are at
    risk of racing with scheduler actions, i.e. single atomic reads need to
    be used there. Obviously the non-init write sites then better also use
    atomic writes.
    
    Having to touch the descriptor table TLB flush code here anyway, take
    the opportunity and switch it to be at most one flush_tlb_mask()
    invocation.
    
    Reported-by: Manuel Bouyer <bouyer@xxxxxxxxxxxxxxx>
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Release-acked-by: Juergen Gross <jgross@xxxxxxxx>
---
 xen/arch/x86/domain.c   |  4 ++--
 xen/arch/x86/mm.c       | 25 +++++++++++++++++++++----
 xen/include/xen/sched.h |  9 +++++++--
 3 files changed, 30 insertions(+), 8 deletions(-)

diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 4ff3d2f3fe..0ca820a00a 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -1621,7 +1621,7 @@ static void __context_switch(void)
      */
     if ( pd != nd )
         cpumask_set_cpu(cpu, nd->dirty_cpumask);
-    n->dirty_cpu = cpu;
+    write_atomic(&n->dirty_cpu, cpu);
 
     if ( !is_idle_domain(nd) )
     {
@@ -1677,7 +1677,7 @@ static void __context_switch(void)
 
     if ( pd != nd )
         cpumask_clear_cpu(cpu, pd->dirty_cpumask);
-    p->dirty_cpu = VCPU_CPU_CLEAN;
+    write_atomic(&p->dirty_cpu, VCPU_CPU_CLEAN);
 
     per_cpu(curr_vcpu, cpu) = n;
 }
diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index f73f43edc9..50b5343899 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -1251,11 +1251,23 @@ void put_page_from_l1e(l1_pgentry_t l1e, struct domain 
*l1e_owner)
              unlikely(((page->u.inuse.type_info & PGT_count_mask) != 0)) &&
              (l1e_owner == pg_owner) )
         {
+            cpumask_t *mask = this_cpu(scratch_cpumask);
+
+            cpumask_clear(mask);
+
             for_each_vcpu ( pg_owner, v )
             {
-                if ( pv_destroy_ldt(v) )
-                    flush_tlb_mask(cpumask_of(v->dirty_cpu));
+                unsigned int cpu;
+
+                if ( !pv_destroy_ldt(v) )
+                    continue;
+                cpu = read_atomic(&v->dirty_cpu);
+                if ( is_vcpu_dirty_cpu(cpu) )
+                    __cpumask_set_cpu(cpu, mask);
             }
+
+            if ( !cpumask_empty(mask) )
+                flush_tlb_mask(mask);
         }
         put_page(page);
     }
@@ -3028,13 +3040,18 @@ static inline int vcpumask_to_pcpumask(
 
         while ( vmask )
         {
+            unsigned int cpu;
+
             vcpu_id = find_first_set_bit(vmask);
             vmask &= ~(1UL << vcpu_id);
             vcpu_id += vcpu_bias;
             if ( (vcpu_id >= d->max_vcpus) )
                 return 0;
-            if ( ((v = d->vcpu[vcpu_id]) != NULL) && vcpu_cpu_dirty(v) )
-                __cpumask_set_cpu(v->dirty_cpu, pmask);
+            if ( (v = d->vcpu[vcpu_id]) == NULL )
+                continue;
+            cpu = read_atomic(&v->dirty_cpu);
+            if ( is_vcpu_dirty_cpu(cpu) )
+                __cpumask_set_cpu(cpu, pmask);
         }
     }
 }
diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index 3aeb6eea77..99d2af2e1f 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -795,10 +795,15 @@ static inline int vcpu_runnable(struct vcpu *v)
              atomic_read(&v->domain->pause_count));
 }
 
-static inline bool vcpu_cpu_dirty(const struct vcpu *v)
+static inline bool is_vcpu_dirty_cpu(unsigned int cpu)
 {
     BUILD_BUG_ON(NR_CPUS >= VCPU_CPU_CLEAN);
-    return v->dirty_cpu != VCPU_CPU_CLEAN;
+    return cpu != VCPU_CPU_CLEAN;
+}
+
+static inline bool vcpu_cpu_dirty(const struct vcpu *v)
+{
+    return is_vcpu_dirty_cpu(v->dirty_cpu);
 }
 
 void vcpu_block(void);
--
generated by git-patchbot for /home/xen/git/xen.git#master

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