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SubjectRe: [PATCH v2 5/6] kvm: allocate vcpu pointer array separately
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On 03.09.21 16:41, Marc Zyngier wrote:
> On Fri, 03 Sep 2021 14:08:06 +0100,
> Juergen Gross <jgross@suse.com> wrote:
>>
>> Prepare support of very large vcpu numbers per guest by moving the
>> vcpu pointer array out of struct kvm.
>>
>> Signed-off-by: Juergen Gross <jgross@suse.com>
>> ---
>> V2:
>> - rebase to new kvm_arch_free_vm() implementation
>> ---
>> arch/arm64/kvm/arm.c | 21 +++++++++++++++++++--
>> arch/x86/include/asm/kvm_host.h | 5 +----
>> arch/x86/kvm/x86.c | 18 ++++++++++++++++++
>> include/linux/kvm_host.h | 17 +++++++++++++++--
>> 4 files changed, 53 insertions(+), 8 deletions(-)
>>
>> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
>> index 38fff5963d9f..8bb5caeba007 100644
>> --- a/arch/arm64/kvm/arm.c
>> +++ b/arch/arm64/kvm/arm.c
>> @@ -293,10 +293,27 @@ long kvm_arch_dev_ioctl(struct file *filp,
>>
>> struct kvm *kvm_arch_alloc_vm(void)
>> {
>> + struct kvm *kvm;
>> +
>> + if (!has_vhe())
>> + kvm = kzalloc(sizeof(struct kvm), GFP_KERNEL);
>> + else
>> + kvm = vzalloc(sizeof(struct kvm));
>> +
>> + if (!kvm)
>> + return NULL;
>> +
>> if (!has_vhe())
>> - return kzalloc(sizeof(struct kvm), GFP_KERNEL);
>> + kvm->vcpus = kcalloc(KVM_MAX_VCPUS, sizeof(void *), GFP_KERNEL);
>> + else
>> + kvm->vcpus = vzalloc(KVM_MAX_VCPUS * sizeof(void *));
>> +
>> + if (!kvm->vcpus) {
>> + kvm_arch_free_vm(kvm);
>> + kvm = NULL;
>> + }
>>
>> - return vzalloc(sizeof(struct kvm));
>> + return kvm;
>> }
>>
>> int kvm_arch_vcpu_precreate(struct kvm *kvm, unsigned int id)
>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>> index f16fadfc030a..6c28d0800208 100644
>> --- a/arch/x86/include/asm/kvm_host.h
>> +++ b/arch/x86/include/asm/kvm_host.h
>> @@ -1517,10 +1517,7 @@ static inline void kvm_ops_static_call_update(void)
>> }
>>
>> #define __KVM_HAVE_ARCH_VM_ALLOC
>> -static inline struct kvm *kvm_arch_alloc_vm(void)
>> -{
>> - return __vmalloc(kvm_x86_ops.vm_size, GFP_KERNEL_ACCOUNT | __GFP_ZERO);
>> -}
>> +struct kvm *kvm_arch_alloc_vm(void);
>>
>> #define __KVM_HAVE_ARCH_VM_FREE
>> void kvm_arch_free_vm(struct kvm *kvm);
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index cc552763f0e4..ff142b6dd00c 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -11126,6 +11126,24 @@ void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu)
>> static_call(kvm_x86_sched_in)(vcpu, cpu);
>> }
>>
>> +struct kvm *kvm_arch_alloc_vm(void)
>> +{
>> + struct kvm *kvm;
>> +
>> + kvm = __vmalloc(kvm_x86_ops.vm_size, GFP_KERNEL_ACCOUNT | __GFP_ZERO);
>> + if (!kvm)
>> + return NULL;
>> +
>> + kvm->vcpus = __vmalloc(KVM_MAX_VCPUS * sizeof(void *),
>> + GFP_KERNEL_ACCOUNT | __GFP_ZERO);
>> + if (!kvm->vcpus) {
>> + vfree(kvm);
>> + kvm = NULL;
>> + }
>> +
>> + return kvm;
>> +}
>> +
>> void kvm_arch_free_vm(struct kvm *kvm)
>> {
>> kfree(to_kvm_hv(kvm)->hv_pa_pg);
>> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
>> index d75e9c2a00b1..9e2a5f1c6f54 100644
>> --- a/include/linux/kvm_host.h
>> +++ b/include/linux/kvm_host.h
>> @@ -536,7 +536,7 @@ struct kvm {
>> struct mutex slots_arch_lock;
>> struct mm_struct *mm; /* userspace tied to this vm */
>> struct kvm_memslots __rcu *memslots[KVM_ADDRESS_SPACE_NUM];
>> - struct kvm_vcpu *vcpus[KVM_MAX_VCPUS];
>> + struct kvm_vcpu **vcpus;
>
> At this stage, I really wonder why we are not using an xarray instead.
>
> I wrote this [1] a while ago, and nothing caught fire. It was also a
> net deletion of code...

Indeed, I'd prefer that solution!

Are you fine with me swapping my patch with yours in the series?


Juergen

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