VMX: fix interaction of APIC-V and Viridian emulation

Viridian using a synthetic MSR for issuing EOI notifications bypasses
the normal in-processor handling, which would clear
GUEST_INTR_STATUS.SVI. Hence we need to do this in software in order
for future interrupts to get delivered.

Based on analysis by Yang Z Zhang <yang.z.zhang@xxxxxxxxx>.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v2: Split off cleanup parts to new patch 3.

--- a/xen/arch/x86/hvm/vlapic.c
+++ b/xen/arch/x86/hvm/vlapic.c
@@ -386,6 +386,9 @@ void vlapic_EOI_set(struct vlapic *vlapi
 
     vlapic_clear_vector(vector, &vlapic->regs->data[APIC_ISR]);
 
+    if ( hvm_funcs.handle_eoi )
+        hvm_funcs.handle_eoi(vector);
+
     if ( vlapic_test_and_clear_vector(vector, &vlapic->regs->data[APIC_TMR]) )
         vioapic_update_EOI(vlapic_domain(vlapic), vector);
 
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -1502,6 +1502,15 @@ static void vmx_sync_pir_to_irr(struct v
         vlapic_set_vector(i, &vlapic->regs->data[APIC_IRR]);
 }
 
+static void vmx_handle_eoi(u8 vector)
+{
+    unsigned long status = __vmread(GUEST_INTR_STATUS);
+
+    /* We need to clear the SVI field. */
+    status &= VMX_GUEST_INTR_STATUS_SUBFIELD_BITMASK;
+    __vmwrite(GUEST_INTR_STATUS, status);
+}
+
 static struct hvm_function_table __initdata vmx_function_table = {
     .name                 = "VMX",
     .cpu_up_prepare       = vmx_cpu_up_prepare,
@@ -1554,6 +1563,7 @@ static struct hvm_function_table __initd
     .process_isr          = vmx_process_isr,
     .deliver_posted_intr  = vmx_deliver_posted_intr,
     .sync_pir_to_irr      = vmx_sync_pir_to_irr,
+    .handle_eoi           = vmx_handle_eoi,
     .nhvm_hap_walk_L1_p2m = nvmx_hap_walk_L1_p2m,
 };
 
@@ -1580,7 +1590,10 @@ const struct hvm_function_table * __init
 
         setup_ept_dump();
     }
- 
+
+    if ( !cpu_has_vmx_virtual_intr_delivery )
+        vmx_function_table.handle_eoi = NULL;
+
     if ( cpu_has_vmx_posted_intr_processing )
         alloc_direct_apic_vector(&posted_intr_vector, event_check_interrupt);
     else
--- a/xen/include/asm-x86/hvm/hvm.h
+++ b/xen/include/asm-x86/hvm/hvm.h
@@ -186,6 +186,7 @@ struct hvm_function_table {
     void (*process_isr)(int isr, struct vcpu *v);
     void (*deliver_posted_intr)(struct vcpu *v, u8 vector);
     void (*sync_pir_to_irr)(struct vcpu *v);
+    void (*handle_eoi)(u8 vector);
 
     /*Walk nested p2m  */
     int (*nhvm_hap_walk_L1_p2m)(struct vcpu *v, paddr_t L2_gpa,