Commit 4fc096a9 authored by Vitaly Kuznetsov's avatar Vitaly Kuznetsov Committed by Paolo Bonzini
Browse files

KVM: Raise the maximum number of user memslots 



Current KVM_USER_MEM_SLOTS limits are arch specific (512 on Power, 509 on x86,
32 on s390, 16 on MIPS) but they don't really need to be. Memory slots are
allocated dynamically in KVM when added so the only real limitation is
'id_to_index' array which is 'short'. We don't have any other
KVM_MEM_SLOTS_NUM/KVM_USER_MEM_SLOTS-sized statically defined structures.

Low KVM_USER_MEM_SLOTS can be a limiting factor for some configurations.
In particular, when QEMU tries to start a Windows guest with Hyper-V SynIC
enabled and e.g. 256 vCPUs the limit is hit as SynIC requires two pages per
vCPU and the guest is free to pick any GFN for each of them, this fragments
memslots as QEMU wants to have a separate memslot for each of these pages
(which are supposed to act as 'overlay' pages).

Signed-off-by: default avatarVitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210127175731.2020089-3-vkuznets@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 281d9cd9

arch/arm64/include/asm/kvm_host.h

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@@ -30,7 +30,6 @@ 


#define __KVM_HAVE_ARCH_INTC_INITIALIZED



#define KVM_USER_MEM_SLOTS 512

#define KVM_HALT_POLL_NS_DEFAULT 500000



#include <kvm/arm_vgic.h>

arch/mips/include/asm/kvm_host.h

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@@ -83,7 +83,6 @@ 




#define KVM_MAX_VCPUS		16

#define KVM_USER_MEM_SLOTS	16

/* memory slots that does not exposed to userspace */

#define KVM_PRIVATE_MEM_SLOTS	0

arch/powerpc/include/asm/kvm_host.h

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@@ -28,7 +28,6 @@ 


#define KVM_MAX_VCPUS		NR_CPUS

#define KVM_MAX_VCORES		NR_CPUS

#define KVM_USER_MEM_SLOTS	512



#include <asm/cputhreads.h>

arch/s390/include/asm/kvm_host.h

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@@ -28,7 +28,6 @@ 
#define KVM_S390_BSCA_CPU_SLOTS 64

#define KVM_S390_ESCA_CPU_SLOTS 248

#define KVM_MAX_VCPUS 255

#define KVM_USER_MEM_SLOTS 32



/*

 * These seem to be used for allocating ->chip in the routing table, which we

arch/x86/include/asm/kvm_host.h

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@@ -40,10 +40,8 @@ 
#define KVM_MAX_VCPUS 288

#define KVM_SOFT_MAX_VCPUS 240

#define KVM_MAX_VCPU_ID 1023

#define KVM_USER_MEM_SLOTS 509

/* memory slots that are not exposed to userspace */

#define KVM_PRIVATE_MEM_SLOTS 3

#define KVM_MEM_SLOTS_NUM (KVM_USER_MEM_SLOTS + KVM_PRIVATE_MEM_SLOTS)



#define KVM_HALT_POLL_NS_DEFAULT 200000