linux-kernel - [PATCH v3 34/35] x86/kvm: Reserve KVM_FEATURE_MSI_EXT_DEST

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Date:   Sat, 24 Oct 2020 22:35:34 +0100
From:   David Woodhouse <dwmw2@...radead.org>
To:     x86@...nel.org
Cc:     kvm <kvm@...r.kernel.org>, iommu@...ts.linux-foundation.org,
        joro@...tes.org, Thomas Gleixner <tglx@...utronix.de>,
        Paolo Bonzini <pbonzini@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-hyperv@...r.kernel.org, maz@...terjones.org,
        Dexuan Cui <decui@...rosoft.com>
Subject: [PATCH v3 34/35] x86/kvm: Reserve KVM_FEATURE_MSI_EXT_DEST_ID

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

No functional change; just reserve the feature bit for now so that VMMs
can start to implement it.

This will allow the host to indicate that 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@...zon.co.uk>
Acked-by: Paolo Bonzini <pbonzini@...hat.com>
---
 Documentation/virt/kvm/cpuid.rst     | 4 ++++
 arch/x86/include/uapi/asm/kvm_para.h | 1 +
 2 files changed, 5 insertions(+)

diff --git a/Documentation/virt/kvm/cpuid.rst b/Documentation/virt/kvm/cpuid.rst
index 9150e9d1c39b..f70b655821d5 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
 
-- 
2.26.2