[PATCH v4 6/6] x86/HVM: report the set of enabled emulated devices through CPUID

[Roger Pau Monne <roger.pau@citrix.com>]

Add a new HVM-specific feature flag that signals the presence of a bitmap
that contains the current set of enabled emulated devices. The bitmap is
placed in the ecx register. The bit fields used in the bitmap are the same
as the ones used in the xen_arch_domainconfig emulation_flags field, and
their meaning can be found at arch-x86/xen.h.

This will allow Xen to enable emulated devices for HVMlite guests in the
future, by having a proper ABI for reporting which devices are enabled.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
---
Cc: Jan Beulich <jbeulich@suse.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
---
 xen/arch/x86/hvm/hvm.c              | 4 ++++
 xen/include/public/arch-x86/cpuid.h | 5 +++++
 2 files changed, 9 insertions(+)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 674feea..f0145f6 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -4536,6 +4536,10 @@ void hvm_hypervisor_cpuid_leaf(uint32_t sub_idx,
         /* Indicate presence of vcpu id and set it in ebx */
         *eax |= XEN_HVM_CPUID_VCPU_ID_PRESENT;
         *ebx = current->vcpu_id;
+
+        /* Indicate the presence of the devices bitmap in ecx. */
+        *eax |= XEN_HVM_CPUID_DEVICES_BITMAP;
+        *ecx = current->domain->arch.emulation_flags;
     }
 }
 
diff --git a/xen/include/public/arch-x86/cpuid.h b/xen/include/public/arch-x86/cpuid.h
index d709340..7222483 100644
--- a/xen/include/public/arch-x86/cpuid.h
+++ b/xen/include/public/arch-x86/cpuid.h
@@ -78,12 +78,17 @@
  * HVM-specific features
  * EAX: Features
  * EBX: vcpu id (iff EAX has XEN_HVM_CPUID_VCPU_ID_PRESENT flag)
+ * ECX: bitmap of enabled devices, according to the bit fields defined in
+ *      arch-x86/xen.h. All unused bits have undefined values. The contents
+ *      of this register is only valid if EAX has the
+ *      XEN_HVM_CPUID_DEVICES_BITMAP flag set.
  */
 #define XEN_HVM_CPUID_APIC_ACCESS_VIRT (1u << 0) /* Virtualized APIC registers */
 #define XEN_HVM_CPUID_X2APIC_VIRT      (1u << 1) /* Virtualized x2APIC accesses */
 /* 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_DEVICES_BITMAP   (1u << 4) /* device bitmap in ECX */
 
 #define XEN_CPUID_MAX_NUM_LEAVES 4
 
-- 
1.9.5 (Apple Git-50.3)


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