arm/arm64: KVM: Remove 'config KVM_ARM_MAX_VCPUS'

This patch removes config option of KVM_ARM_MAX_VCPUS,
and like other ARCHs, just choose the maximum allowed
value from hardware, and follows the reasons:

1) from distribution view, the option has to be
defined as the max allowed value because it need to
meet all kinds of virtulization applications and
need to support most of SoCs;

2) using a bigger value doesn't introduce extra memory
consumption, and the help text in Kconfig isn't accurate
because kvm_vpu structure isn't allocated until request
of creating VCPU is sent from QEMU;

3) the main effect is that the field of vcpus[] in 'struct kvm'
becomes a bit bigger(sizeof(void *) per vcpu) and need more cache
lines to hold the structure, but 'struct kvm' is one generic struct,
and it has worked well on other ARCHs already in this way. Also,
the world switch frequecy is often low, for example, it is ~2000
when running kernel building load in VM from APM xgene KVM host,
so the effect is very small, and the difference can't be observed
in my test at all.

Cc: Dann Frazier <dann.frazier@canonical.com>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

arch/arm/include/asm/kvm_host.h

@@ -29,12 +29,6 @@
 
 #define __KVM_HAVE_ARCH_INTC_INITIALIZED
 
-#if defined(CONFIG_KVM_ARM_MAX_VCPUS)
-#define KVM_MAX_VCPUS CONFIG_KVM_ARM_MAX_VCPUS
-#else
-#define KVM_MAX_VCPUS 0
-#endif
-
 #define KVM_USER_MEM_SLOTS 32
 #define KVM_PRIVATE_MEM_SLOTS 4
 #define KVM_COALESCED_MMIO_PAGE_OFFSET 1
@@ -44,6 +38,8 @@
 
 #include <kvm/arm_vgic.h>
 
+#define KVM_MAX_VCPUS VGIC_V2_MAX_CPUS
+
 u32 *kvm_vcpu_reg(struct kvm_vcpu *vcpu, u8 reg_num, u32 mode);
 int __attribute_const__ kvm_target_cpu(void);
 int kvm_reset_vcpu(struct kvm_vcpu *vcpu);

arch/arm/kvm/Kconfig

@@ -45,15 +45,4 @@ config KVM_ARM_HOST
 	---help---
 	  Provides host support for ARM processors.
 
-config KVM_ARM_MAX_VCPUS
-	int "Number maximum supported virtual CPUs per VM"
-	depends on KVM_ARM_HOST
-	default 4
-	help
-	  Static number of max supported virtual CPUs per VM.
-
-	  If you choose a high number, the vcpu structures will be quite
-	  large, so only choose a reasonable number that you expect to
-	  actually use.
-
 endif # VIRTUALIZATION

arch/arm64/include/asm/kvm_host.h

@@ -30,19 +30,15 @@
 
 #define __KVM_HAVE_ARCH_INTC_INITIALIZED
 
-#if defined(CONFIG_KVM_ARM_MAX_VCPUS)
-#define KVM_MAX_VCPUS CONFIG_KVM_ARM_MAX_VCPUS
-#else
-#define KVM_MAX_VCPUS 0
-#endif
-
 #define KVM_USER_MEM_SLOTS 32
 #define KVM_PRIVATE_MEM_SLOTS 4
 #define KVM_COALESCED_MMIO_PAGE_OFFSET 1
 
 #include <kvm/arm_vgic.h>
 #include <kvm/arm_arch_timer.h>
 
+#define KVM_MAX_VCPUS VGIC_V3_MAX_CPUS
+
 #define KVM_VCPU_MAX_FEATURES 3
 
 int __attribute_const__ kvm_target_cpu(void);

arch/arm64/kvm/Kconfig

@@ -41,15 +41,4 @@ config KVM_ARM_HOST
 	---help---
 	  Provides host support for ARM processors.
 
-config KVM_ARM_MAX_VCPUS
-	int "Number maximum supported virtual CPUs per VM"
-	depends on KVM_ARM_HOST
-	default 4
-	help
-	  Static number of max supported virtual CPUs per VM.
-
-	  If you choose a high number, the vcpu structures will be quite
-	  large, so only choose a reasonable number that you expect to
-	  actually use.
-
 endif # VIRTUALIZATION

include/kvm/arm_vgic.h

@@ -35,11 +35,7 @@
 #define VGIC_V3_MAX_LRS		16
 #define VGIC_MAX_IRQS		1024
 #define VGIC_V2_MAX_CPUS	8
-
-/* Sanity checks... */
-#if (KVM_MAX_VCPUS > 255)
-#error Too many KVM VCPUs, the VGIC only supports up to 255 VCPUs for now
-#endif
+#define VGIC_V3_MAX_CPUS	255
 
 #if (VGIC_NR_IRQS_LEGACY & 31)
 #error "VGIC_NR_IRQS must be a multiple of 32"

virt/kvm/arm/vgic-v3.c

@@ -288,7 +288,7 @@ int vgic_v3_probe(struct device_node *vgic_node,
 
 	vgic->vctrl_base = NULL;
 	vgic->type = VGIC_V3;
-	vgic->max_gic_vcpus = KVM_MAX_VCPUS;
+	vgic->max_gic_vcpus = VGIC_V3_MAX_CPUS;
 
 	kvm_info("%s@%llx IRQ%d\n", vgic_node->name,
 		 vcpu_res.start, vgic->maint_irq);