[Xen-devel] [PATCH] x86/hvm/viridian: fix the TLB flush hypercall

[Paul Durrant <paul.durrant@xxxxxxxxxx>]

Commit b38d426a "flush remote tlbs by hypercall" add support to allow
Windows to request flush of remote TLB via hypercall rather than IPI.
Unfortunately it seems that this code was broken in a couple of ways:

1) The allocation of the per-vcpu flush mask is gated on whether the
   domain has viridian features enabled but the call to allocate is
   made before the toolstack has enabled those features. This results
   in a NULL pointer dereference.

2) One of the flush hypercall variants is a rep op, but the code
   does not update the output data with the reps completed. Hence the
   guest will spin repeatedly making the hypercall because it believes
   it has uncompleted reps.

This patch fixes both of these issues and also adds a check to make
sure the current vCPU is not included in the flush mask (since there's
clearly no need for the CPU to IPI itself).

Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
---
 xen/arch/x86/hvm/hvm.c      | 12 ++++--------
 xen/arch/x86/hvm/viridian.c |  4 +++-
 2 files changed, 7 insertions(+), 9 deletions(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 5bc2812..f5c55e1 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -2576,12 +2576,9 @@ int hvm_vcpu_initialise(struct vcpu *v)
     if ( rc != 0 )
         goto fail6;
 
-    if ( is_viridian_domain(d) )
-    {
-        rc = viridian_vcpu_init(v);
-        if ( rc != 0 )
-            goto fail7;
-    }
+    rc = viridian_vcpu_init(v);
+    if ( rc != 0 )
+        goto fail7;
 
     if ( v->vcpu_id == 0 )
     {
@@ -2615,8 +2612,7 @@ int hvm_vcpu_initialise(struct vcpu *v)
 
 void hvm_vcpu_destroy(struct vcpu *v)
 {
-    if ( is_viridian_domain(v->domain) )
-        viridian_vcpu_deinit(v);
+    viridian_vcpu_deinit(v);
 
     hvm_all_ioreq_servers_remove_vcpu(v->domain, v);
 
diff --git a/xen/arch/x86/hvm/viridian.c b/xen/arch/x86/hvm/viridian.c
index 6bd844b..6530a67 100644
--- a/xen/arch/x86/hvm/viridian.c
+++ b/xen/arch/x86/hvm/viridian.c
@@ -645,7 +645,7 @@ int viridian_hypercall(struct cpu_user_regs *regs)
                 continue;
 
             hvm_asid_flush_vcpu(v);
-            if ( v->is_running )
+            if ( v != curr && v->is_running )
                 __cpumask_set_cpu(v->processor, pcpu_mask);
         }
 
@@ -658,6 +658,8 @@ int viridian_hypercall(struct cpu_user_regs *regs)
         if ( !cpumask_empty(pcpu_mask) )
             flush_tlb_mask(pcpu_mask);
 
+        output.rep_complete = input.rep_count;
+
         status = HV_STATUS_SUCCESS;
         break;
     }
-- 
2.1.4


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