[Xen-devel] [PATCH v2] 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 ipi 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 as follows:

1) The ipi mask need only be per-pcpu so it is made a per-pcpu static
   to avoid the need for allocation.

2) The rep complete count is updated to the rep count since the single
   flush that Xen does covers all reps anyway.

Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
Cc: Keir Fraser <keir@xxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---

v2:
 - Move to per-pcpu ipi mask.
 - Use smp_send_event_check_mask() to IPI rather than flush_tlb_mask().
---
 xen/arch/x86/hvm/hvm.c             | 12 ------------
 xen/arch/x86/hvm/viridian.c        | 19 ++++++-------------
 xen/include/asm-x86/hvm/viridian.h |  4 ----
 3 files changed, 6 insertions(+), 29 deletions(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 5bc2812..4ea51d7 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -2576,13 +2576,6 @@ 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;
-    }
-
     if ( v->vcpu_id == 0 )
     {
         /* NB. All these really belong in hvm_domain_initialise(). */
@@ -2597,8 +2590,6 @@ int hvm_vcpu_initialise(struct vcpu *v)
 
     return 0;
 
- fail7:
-    hvm_all_ioreq_servers_remove_vcpu(v->domain, v);
  fail6:
     nestedhvm_vcpu_destroy(v);
  fail5:
@@ -2615,9 +2606,6 @@ int hvm_vcpu_initialise(struct vcpu *v)
 
 void hvm_vcpu_destroy(struct vcpu *v)
 {
-    if ( is_viridian_domain(v->domain) )
-        viridian_vcpu_deinit(v);
-
     hvm_all_ioreq_servers_remove_vcpu(v->domain, v);
 
     if ( hvm_altp2m_supported() )
diff --git a/xen/arch/x86/hvm/viridian.c b/xen/arch/x86/hvm/viridian.c
index 6bd844b..1ee22aa 100644
--- a/xen/arch/x86/hvm/viridian.c
+++ b/xen/arch/x86/hvm/viridian.c
@@ -521,16 +521,7 @@ int rdmsr_viridian_regs(uint32_t idx, uint64_t *val)
     return 1;
 }
 
-int viridian_vcpu_init(struct vcpu *v)
-{
-    return alloc_cpumask_var(&v->arch.hvm_vcpu.viridian.flush_cpumask) ?
-           0 : -ENOMEM;
-}
-
-void viridian_vcpu_deinit(struct vcpu *v)
-{
-    free_cpumask_var(v->arch.hvm_vcpu.viridian.flush_cpumask);
-}
+static DEFINE_PER_CPU(cpumask_t, ipi_cpumask);
 
 int viridian_hypercall(struct cpu_user_regs *regs)
 {
@@ -627,7 +618,7 @@ int viridian_hypercall(struct cpu_user_regs *regs)
         if ( input_params.flags & HV_FLUSH_ALL_PROCESSORS )
             input_params.vcpu_mask = ~0ul;
 
-        pcpu_mask = curr->arch.hvm_vcpu.viridian.flush_cpumask;
+        pcpu_mask = &this_cpu(ipi_cpumask);
         cpumask_clear(pcpu_mask);
 
         /*
@@ -645,7 +636,7 @@ 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);
         }
 
@@ -656,7 +647,9 @@ int viridian_hypercall(struct cpu_user_regs *regs)
          * so we may unnecessarily IPI some CPUs.
          */
         if ( !cpumask_empty(pcpu_mask) )
-            flush_tlb_mask(pcpu_mask);
+            smp_send_event_check_mask(pcpu_mask);
+
+        output.rep_complete = input.rep_count;
 
         status = HV_STATUS_SUCCESS;
         break;
diff --git a/xen/include/asm-x86/hvm/viridian.h 
b/xen/include/asm-x86/hvm/viridian.h
index 2eec85e..c4319d7 100644
--- a/xen/include/asm-x86/hvm/viridian.h
+++ b/xen/include/asm-x86/hvm/viridian.h
@@ -22,7 +22,6 @@ union viridian_apic_assist
 struct viridian_vcpu
 {
     union viridian_apic_assist apic_assist;
-    cpumask_var_t flush_cpumask;
 };
 
 union viridian_guest_os_id
@@ -118,9 +117,6 @@ viridian_hypercall(struct cpu_user_regs *regs);
 void viridian_time_ref_count_freeze(struct domain *d);
 void viridian_time_ref_count_thaw(struct domain *d);
 
-int viridian_vcpu_init(struct vcpu *v);
-void viridian_vcpu_deinit(struct vcpu *v);
-
 #endif /* __ASM_X86_HVM_VIRIDIAN_H__ */
 
 /*
-- 
2.1.4


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