linux-kernel - [PATCH v2] KVM: x86: Add CONFIG_KVM_MAX_NR

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Date:   Wed, 23 Aug 2023 14:38:43 -0500
From:   Kyle Meyer <kyle.meyer@....com>
To:     seanjc@...gle.com, pbonzini@...hat.com, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...el.com,
        x86@...nel.org, hpa@...or.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, vkuznets@...hat.com,
        dmatlack@...gle.com
Cc:     russ.anderson@....com, dimitri.sivanich@....com,
        steve.wahl@....com, Kyle Meyer <kyle.meyer@....com>
Subject: [PATCH v2] KVM: x86: Add CONFIG_KVM_MAX_NR_VCPUS

Add a Kconfig entry to set the maximum number of vCPUs per KVM guest and
set the default value to 4096 when MAXSMP is enabled.

Suggested-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Kyle Meyer <kyle.meyer@....com>
---
 arch/x86/include/asm/kvm_host.h |  2 +-
 arch/x86/kvm/Kconfig            | 11 +++++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 3bc146dfd38d..536317812b52 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -39,7 +39,7 @@
 
 #define __KVM_HAVE_ARCH_VCPU_DEBUGFS
 
-#define KVM_MAX_VCPUS 1024
+#define KVM_MAX_VCPUS CONFIG_KVM_MAX_NR_VCPUS
 
 /*
  * In x86, the VCPU ID corresponds to the APIC ID, and APIC IDs
diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index 89ca7f4c1464..e730e8255e22 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -141,4 +141,15 @@ config KVM_XEN
 config KVM_EXTERNAL_WRITE_TRACKING
 	bool
 
+config KVM_MAX_NR_VCPUS
+	int "Maximum number of vCPUs per KVM guest"
+	depends on KVM
+	range 1024 4096
+	default 4096 if MAXSMP
+	default 1024
+	help
+	  Set the maximum number of vCPUs per KVM guest. Larger values will increase
+	  the memory footprint of each KVM guest, regardless of how many vCPUs are
+	  configured.
+
 endif # VIRTUALIZATION
-- 
2.26.2