[PATCH v2] x86/hvm/viridian: save APIC assist vector

[Paul Durrant <paul.durrant@citrix.com>]

If any vcpu has a pending APIC assist when the domain is suspended
then the vector needs to be saved. If this is not done then it's
possible for the vector to remain pending in the vlapic ISR
indefinitely after resume.

This patch adds code to save the APIC assist vector value in the
viridian vcpu save record. This means that the record is now zero-
extended on load and, because this implies a loaded value of
zero means nothing is pending (for backwards compatibility with
hosts not implementing APIC assist), the rest of the viridian APIC
assist code is adjusted to treat a zero value in this way. A
check has therefore been added to viridian_start_apic_assist() to
prevent the enlightenment being used for vectors < 0x10 (which
are illegal for an APIC).

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Cc: Jan Beulich <jbeulich@suse.com>
---

v2:
 - don't use biasing
 - add missing padding to save record
---
 xen/arch/x86/hvm/viridian.c            | 23 ++++++++++++++---------
 xen/arch/x86/hvm/vlapic.c              |  2 +-
 xen/include/public/arch-x86/hvm/save.h |  4 +++-
 3 files changed, 18 insertions(+), 11 deletions(-)

diff --git a/xen/arch/x86/hvm/viridian.c b/xen/arch/x86/hvm/viridian.c
index 410320c..dceed2c 100644
--- a/xen/arch/x86/hvm/viridian.c
+++ b/xen/arch/x86/hvm/viridian.c
@@ -252,7 +252,6 @@ static void initialize_apic_assist(struct vcpu *v)
     if ( viridian_feature_mask(v->domain) & HVMPV_apic_assist )
     {
         v->arch.hvm_vcpu.viridian.apic_assist.va = va;
-        v->arch.hvm_vcpu.viridian.apic_assist.vector = -1;
         return;
     }
 
@@ -288,12 +287,15 @@ void viridian_start_apic_assist(struct vcpu *v, int vector)
     if ( !va )
         return;
 
+    if ( vector < 0x10 )
+        return;
+
     /*
      * If there is already an assist pending then something has gone
      * wrong and the VM will most likely hang so force a crash now
      * to make the problem clear.
      */
-    if ( v->arch.hvm_vcpu.viridian.apic_assist.vector >= 0 )
+    if ( v->arch.hvm_vcpu.viridian.apic_assist.vector )
         domain_crash(v->domain);
 
     v->arch.hvm_vcpu.viridian.apic_assist.vector = vector;
@@ -306,13 +308,13 @@ int viridian_complete_apic_assist(struct vcpu *v)
     int vector;
 
     if ( !va )
-        return -1;
+        return 0;
 
     if ( *va & 1u )
-        return -1; /* Interrupt not yet processed by the guest. */
+        return 0; /* Interrupt not yet processed by the guest. */
 
     vector = v->arch.hvm_vcpu.viridian.apic_assist.vector;
-    v->arch.hvm_vcpu.viridian.apic_assist.vector = -1;
+    v->arch.hvm_vcpu.viridian.apic_assist.vector = 0;
 
     return vector;
 }
@@ -325,7 +327,7 @@ void viridian_abort_apic_assist(struct vcpu *v)
         return;
 
     *va &= ~1u;
-    v->arch.hvm_vcpu.viridian.apic_assist.vector = -1;
+    v->arch.hvm_vcpu.viridian.apic_assist.vector = 0;
 }
 
 static void update_reference_tsc(struct domain *d, bool_t initialize)
@@ -806,7 +808,8 @@ static int viridian_save_vcpu_ctxt(struct domain *d, hvm_domain_context_t *h)
     for_each_vcpu( d, v ) {
         struct hvm_viridian_vcpu_context ctxt;
 
-        ctxt.apic_assist = v->arch.hvm_vcpu.viridian.apic_assist.msr.raw;
+        ctxt.apic_assist_msr = v->arch.hvm_vcpu.viridian.apic_assist.msr.raw;
+        ctxt.apic_assist_vector = v->arch.hvm_vcpu.viridian.apic_assist.vector;
 
         if ( hvm_save_entry(VIRIDIAN_VCPU, v->vcpu_id, h, &ctxt) != 0 )
             return 1;
@@ -829,13 +832,15 @@ static int viridian_load_vcpu_ctxt(struct domain *d, hvm_domain_context_t *h)
         return -EINVAL;
     }
 
-    if ( hvm_load_entry(VIRIDIAN_VCPU, h, &ctxt) != 0 )
+    if ( hvm_load_entry_zeroextend(VIRIDIAN_VCPU, h, &ctxt) != 0 )
         return -EINVAL;
 
-    v->arch.hvm_vcpu.viridian.apic_assist.msr.raw = ctxt.apic_assist;
+    v->arch.hvm_vcpu.viridian.apic_assist.msr.raw = ctxt.apic_assist_msr;
     if ( v->arch.hvm_vcpu.viridian.apic_assist.msr.fields.enabled )
         initialize_apic_assist(v);
 
+    v->arch.hvm_vcpu.viridian.apic_assist.vector = ctxt.apic_assist_vector;
+
     return 0;
 }
 
diff --git a/xen/arch/x86/hvm/vlapic.c b/xen/arch/x86/hvm/vlapic.c
index f36eff7..e2f4450 100644
--- a/xen/arch/x86/hvm/vlapic.c
+++ b/xen/arch/x86/hvm/vlapic.c
@@ -1189,7 +1189,7 @@ int vlapic_has_pending_irq(struct vcpu *v)
      * comparing with the IRR.
      */
     vector = viridian_complete_apic_assist(v);
-    if ( vector != -1 )
+    if ( vector )
         vlapic_clear_vector(vector, &vlapic->regs->data[APIC_ISR]);
 
     isr = vlapic_find_highest_isr(vlapic);
diff --git a/xen/include/public/arch-x86/hvm/save.h b/xen/include/public/arch-x86/hvm/save.h
index fbd1c6a..8d73b51 100644
--- a/xen/include/public/arch-x86/hvm/save.h
+++ b/xen/include/public/arch-x86/hvm/save.h
@@ -588,7 +588,9 @@ struct hvm_viridian_domain_context {
 DECLARE_HVM_SAVE_TYPE(VIRIDIAN_DOMAIN, 15, struct hvm_viridian_domain_context);
 
 struct hvm_viridian_vcpu_context {
-    uint64_t apic_assist;
+    uint64_t apic_assist_msr;
+    uint8_t  apic_assist_vector;
+    uint8_t  _pad[7];
 };
 
 DECLARE_HVM_SAVE_TYPE(VIRIDIAN_VCPU, 17, struct hvm_viridian_vcpu_context);
-- 
2.1.4


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