linux-kernel - [PATCH v11 017/113] KVM: Support KVM_CAP_MAX_VCPUS for KVM_ENABLE

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Message-Id: <01e061779b88ce4d32bbe483ed2bd3224cd8e330.1673539699.git.isaku.yamahata@intel.com>
Date:   Thu, 12 Jan 2023 08:31:25 -0800
From:   isaku.yamahata@...el.com
To:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     isaku.yamahata@...el.com, isaku.yamahata@...il.com,
        Paolo Bonzini <pbonzini@...hat.com>, erdemaktas@...gle.com,
        Sean Christopherson <seanjc@...gle.com>,
        Sagi Shahar <sagis@...gle.com>,
        David Matlack <dmatlack@...gle.com>
Subject: [PATCH v11 017/113] KVM: Support KVM_CAP_MAX_VCPUS for KVM_ENABLE_CAP

From: Isaku Yamahata <isaku.yamahata@...el.com>

TDX attestation includes the maximum number of vcpu that the guest can
accommodate.  For that, the maximum number of vcpu needs to be specified
instead of constant, KVM_MAX_VCPUS.  Make KVM_ENABLE_CAP support
KVM_CAP_MAX_VCPUS.

Suggested-by: Sagi Shahar <sagis@...gle.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
---
 virt/kvm/kvm_main.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index a235b628b32f..1cfa7da92ad0 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -4945,7 +4945,27 @@ static int kvm_vm_ioctl_enable_cap_generic(struct kvm *kvm,
 		}
 
 		mutex_unlock(&kvm->slots_lock);
+		return r;
+	}
+	case KVM_CAP_MAX_VCPUS: {
+		int r;
 
+		if (cap->flags || cap->args[0] == 0)
+			return -EINVAL;
+		if (cap->args[0] >  kvm_vm_ioctl_check_extension(kvm, KVM_CAP_MAX_VCPUS))
+			return -E2BIG;
+
+		mutex_lock(&kvm->lock);
+		/* Only decreasing is allowed. */
+		if (cap->args[0] > kvm->max_vcpus)
+			r = -E2BIG;
+		else if (kvm->created_vcpus)
+			r = -EBUSY;
+		else {
+			kvm->max_vcpus = cap->args[0];
+			r = 0;
+		}
+		mutex_unlock(&kvm->lock);
 		return r;
 	}
 	default:
-- 
2.25.1