[Xen-devel] [PATCH v8 3/3] x86/hvm: Indicate avaliability of HW support of APIC virtualization to HVM guests

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

Set bits in hypervisor CPUID leaf indicating that HW provides (and the
hypervisor enables) HW support for APIC and x2APIC virtualization.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
---
 xen/arch/x86/hvm/vmx/vmx.c          |   21 +++++++++++++++++++++
 xen/include/public/arch-x86/cpuid.h |    4 ++++
 2 files changed, 25 insertions(+), 0 deletions(-)

diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 180cf6c..7c7acd6 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -57,6 +57,7 @@
 #include <asm/apic.h>
 #include <asm/hvm/nestedhvm.h>
 #include <asm/event.h>
+#include <public/arch-x86/cpuid.h>
 
 enum handler_return { HNDL_done, HNDL_unhandled, HNDL_exception_raised };
 
@@ -1651,6 +1652,25 @@ static void vmx_handle_eoi(u8 vector)
     __vmwrite(GUEST_INTR_STATUS, status);
 }
 
+void vmx_hypervisor_cpuid_leaf(uint32_t sub_idx,
+                               uint32_t *eax, uint32_t *ebx,
+                               uint32_t *ecx, uint32_t *edx)
+{
+    if ( sub_idx != 0 )
+        return;
+
+    if ( cpu_has_vmx_apic_reg_virt )
+        *eax |= XEN_HVM_CPUID_APIC_ACCESS_VIRT;
+    /*
+     * We want to claim that x2APIC is virtualized if APIC MSR accesses are
+     * not intercepted. When all three of these are true both rdmsr and wrmsr
+     * in the guest will run without VMEXITs (see vmx_vlapic_msr_changed()).
+     */
+    if ( cpu_has_vmx_virtualize_x2apic_mode && cpu_has_vmx_apic_reg_virt &&
+         cpu_has_vmx_virtual_intr_delivery)
+        *eax |= XEN_HVM_CPUID_X2APIC_VIRT;
+}
+
 static struct hvm_function_table __initdata vmx_function_table = {
     .name                 = "VMX",
     .cpu_up_prepare       = vmx_cpu_up_prepare,
@@ -1708,6 +1728,7 @@ static struct hvm_function_table __initdata 
vmx_function_table = {
     .sync_pir_to_irr      = vmx_sync_pir_to_irr,
     .handle_eoi           = vmx_handle_eoi,
     .nhvm_hap_walk_L1_p2m = nvmx_hap_walk_L1_p2m,
+    .hypervisor_cpuid_leaf= vmx_hypervisor_cpuid_leaf,
 };
 
 const struct hvm_function_table * __init start_vmx(void)
diff --git a/xen/include/public/arch-x86/cpuid.h 
b/xen/include/public/arch-x86/cpuid.h
index fff972a..7135d54 100644
--- a/xen/include/public/arch-x86/cpuid.h
+++ b/xen/include/public/arch-x86/cpuid.h
@@ -70,6 +70,10 @@
  * HVM-specific features
  */
 
+/* EAX Features */
+#define XEN_HVM_CPUID_APIC_ACCESS_VIRT (1u << 0) /* Virtualized APIC registers 
*/
+#define XEN_HVM_CPUID_X2APIC_VIRT      (1u << 1) /* Virtualized x2APIC 
accesses */
+
 #define XEN_CPUID_MAX_NUM_LEAVES 4
 
 #endif /* __XEN_PUBLIC_ARCH_X86_CPUID_H__ */
-- 
1.7.1


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