xen/x86: detect support for extended destination ID

Xen allows the usage of some previously reserved bits in the IO-APIC
RTE and the MSI address fields in order to store high bits for the
target APIC ID. Such feature is already implemented by QEMU/KVM and
HyperV, so in order to enable it just add the handler that checks for
it's presence.

Signed-off-by: Roger Pau Monné <[email protected]>
Reviewed-by: Juergen Gross <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Juergen Gross <[email protected]>

Author: royger

arch/x86/include/asm/xen/cpuid.h

@@ -100,6 +100,13 @@
 /* Memory mapped from other domains has valid IOMMU entries */
 #define XEN_HVM_CPUID_IOMMU_MAPPINGS   (1u << 2)
 #define XEN_HVM_CPUID_VCPU_ID_PRESENT  (1u << 3) /* vcpu id is present in EBX */
+#define XEN_HVM_CPUID_DOMID_PRESENT    (1u << 4) /* domid is present in ECX */
+/*
+ * Bits 55:49 from the IO-APIC RTE and bits 11:5 from the MSI address can be
+ * used to store high bits for the Destination ID. This expands the Destination
+ * ID field from 8 to 15 bits, allowing to target APIC IDs up 32768.
+ */
+#define XEN_HVM_CPUID_EXT_DEST_ID      (1u << 5)
 
 /*
  * Leaf 6 (0x40000x05)

arch/x86/xen/enlighten_hvm.c

@@ -248,6 +248,11 @@ static __init bool xen_x2apic_available(void)
 	return x2apic_supported();
 }
 
+static bool __init msi_ext_dest_id(void)
+{
+       return cpuid_eax(xen_cpuid_base() + 4) & XEN_HVM_CPUID_EXT_DEST_ID;
+}
+
 static __init void xen_hvm_guest_late_init(void)
 {
 #ifdef CONFIG_XEN_PVH
@@ -310,6 +315,7 @@ struct hypervisor_x86 x86_hyper_xen_hvm __initdata = {
 	.init.x2apic_available  = xen_x2apic_available,
 	.init.init_mem_mapping	= xen_hvm_init_mem_mapping,
 	.init.guest_late_init	= xen_hvm_guest_late_init,
+	.init.msi_ext_dest_id   = msi_ext_dest_id,
 	.runtime.pin_vcpu       = xen_pin_vcpu,
 	.ignore_nopv            = true,
 };