[PATCH 5/5] x86/kvm: Add KVM_FEATURE_MSI_EXT_DEST_ID

[David Woodhouse <dwmw2@infradead.org>]

From: David Woodhouse <dwmw@amazon.co.uk>

This allows the host to indicate that IOAPIC and MSI emulation supports
15-bit destination IDs, allowing up to 32768 CPUs without interrupt
remapping.

cf. https://patchwork.kernel.org/patch/11816693/ for qemu

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
---
 Documentation/virt/kvm/cpuid.rst     | 4 ++++
 arch/x86/include/uapi/asm/kvm_para.h | 1 +
 arch/x86/kernel/kvm.c                | 6 ++++++
 3 files changed, 11 insertions(+)

diff --git a/Documentation/virt/kvm/cpuid.rst b/Documentation/virt/kvm/cpuid.rst
index a7dff9186bed..1726b5925d2b 100644
--- a/Documentation/virt/kvm/cpuid.rst
+++ b/Documentation/virt/kvm/cpuid.rst
@@ -92,6 +92,10 @@ KVM_FEATURE_ASYNC_PF_INT          14          guest checks this feature bit
                                               async pf acknowledgment msr
                                               0x4b564d07.
 
+KVM_FEATURE_MSI_EXT_DEST_ID       15          guest checks this feature bit
+                                              before using extended destination
+                                              ID bits in MSI address bits 11-5.
+
 KVM_FEATURE_CLOCSOURCE_STABLE_BIT 24          host will warn if no guest-side
                                               per-cpu warps are expeced in
                                               kvmclock
diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h
index 812e9b4c1114..950afebfba88 100644
--- a/arch/x86/include/uapi/asm/kvm_para.h
+++ b/arch/x86/include/uapi/asm/kvm_para.h
@@ -32,6 +32,7 @@
 #define KVM_FEATURE_POLL_CONTROL	12
 #define KVM_FEATURE_PV_SCHED_YIELD	13
 #define KVM_FEATURE_ASYNC_PF_INT	14
+#define KVM_FEATURE_MSI_EXT_DEST_ID	15
 
 #define KVM_HINTS_REALTIME      0
 
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 1b51b727b140..4986b4399aef 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -743,12 +743,18 @@ static void __init kvm_init_platform(void)
 	x86_platform.apic_post_init = kvm_apic_init;
 }
 
+static bool __init kvm_msi_ext_dest_id(void)
+{
+	return kvm_para_has_feature(KVM_FEATURE_MSI_EXT_DEST_ID);
+}
+
 const __initconst struct hypervisor_x86 x86_hyper_kvm = {
 	.name			= "KVM",
 	.detect			= kvm_detect,
 	.type			= X86_HYPER_KVM,
 	.init.guest_late_init	= kvm_guest_init,
 	.init.x2apic_available	= kvm_para_available,
+	.init.msi_ext_dest_id	= kvm_msi_ext_dest_id,
 	.init.init_platform	= kvm_init_platform,
 };
 
-- 
2.26.2