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On 13/03/18 21:03, Peng Hao wrote:
> Using a global per-CPU variable instead of per-VM's per-CPU variable.
> 
> Signed-off-by: Peng Hao <peng.h...@zte.com.cn>
> ---
>  arch/arm/include/asm/kvm_host.h   |  3 ---
>  arch/arm64/include/asm/kvm_host.h |  3 ---
>  virt/kvm/arm/arm.c                | 26 ++++++--------------------
>  3 files changed, 6 insertions(+), 26 deletions(-)
> 
> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> index 248b930..4224f3b 100644
> --- a/arch/arm/include/asm/kvm_host.h
> +++ b/arch/arm/include/asm/kvm_host.h
> @@ -59,9 +59,6 @@ struct kvm_arch {
>       /* VTTBR value associated with below pgd and vmid */
>       u64    vttbr;
>  
> -     /* The last vcpu id that ran on each physical CPU */
> -     int __percpu *last_vcpu_ran;
> -
>       /*
>        * Anything that is not used directly from assembly code goes
>        * here.
> diff --git a/arch/arm64/include/asm/kvm_host.h 
> b/arch/arm64/include/asm/kvm_host.h
> index 596f8e4..5035a08 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -67,9 +67,6 @@ struct kvm_arch {
>       /* VTTBR value associated with above pgd and vmid */
>       u64    vttbr;
>  
> -     /* The last vcpu id that ran on each physical CPU */
> -     int __percpu *last_vcpu_ran;
> -
>       /* The maximum number of vCPUs depends on the used GIC model */
>       int max_vcpus;
>  
> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index 86941f6..a67ffb0 100644
> --- a/virt/kvm/arm/arm.c
> +++ b/virt/kvm/arm/arm.c
> @@ -59,6 +59,8 @@
>  /* Per-CPU variable containing the currently running vcpu. */
>  static DEFINE_PER_CPU(struct kvm_vcpu *, kvm_arm_running_vcpu);
>  
> +static DEFINE_PER_CPU(struct kvm_vcpu *, kvm_last_ran_vcpu);
> +
>  /* The VMID used in the VTTBR */
>  static atomic64_t kvm_vmid_gen = ATOMIC64_INIT(1);
>  static u32 kvm_next_vmid;
> @@ -115,18 +117,11 @@ void kvm_arch_check_processor_compat(void *rtn)
>   */
>  int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>  {
> -     int ret, cpu;
> +     int ret;
>  
>       if (type)
>               return -EINVAL;
>  
> -     kvm->arch.last_vcpu_ran = 
> alloc_percpu(typeof(*kvm->arch.last_vcpu_ran));
> -     if (!kvm->arch.last_vcpu_ran)
> -             return -ENOMEM;
> -
> -     for_each_possible_cpu(cpu)
> -             *per_cpu_ptr(kvm->arch.last_vcpu_ran, cpu) = -1;
> -
>       ret = kvm_alloc_stage2_pgd(kvm);
>       if (ret)
>               goto out_fail_alloc;
> @@ -147,9 +142,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>       return ret;
>  out_free_stage2_pgd:
>       kvm_free_stage2_pgd(kvm);
> -out_fail_alloc:
> -     free_percpu(kvm->arch.last_vcpu_ran);
> -     kvm->arch.last_vcpu_ran = NULL;
> +out_fail_alloc:
>       return ret;
>  }
>  
> @@ -179,9 +172,6 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
>  
>       kvm_vgic_destroy(kvm);
>  
> -     free_percpu(kvm->arch.last_vcpu_ran);
> -     kvm->arch.last_vcpu_ran = NULL;
> -
>       for (i = 0; i < KVM_MAX_VCPUS; ++i) {
>               if (kvm->vcpus[i]) {
>                       kvm_arch_vcpu_free(kvm->vcpus[i]);
> @@ -343,17 +333,13 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
>  
>  void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
>  {
> -     int *last_ran;
> -
> -     last_ran = this_cpu_ptr(vcpu->kvm->arch.last_vcpu_ran);
> -
>       /*
>        * We might get preempted before the vCPU actually runs, but
>        * over-invalidation doesn't affect correctness.
>        */
> -     if (*last_ran != vcpu->vcpu_id) {
> +     if (per_cpu(kvm_last_ran_vcpu, cpu) != vcpu) {
>               kvm_call_hyp(__kvm_tlb_flush_local_vmid, vcpu);
> -             *last_ran = vcpu->vcpu_id;
> +             per_cpu(kvm_last_ran_vcpu, cpu) = vcpu;
>       }
>  
>       vcpu->cpu = cpu;
> 

Have you read and understood what this code is about? The whole point of
this code is to track physical CPUs on a per-VM basis. Making it global
completely defeats the point, and can result in guest memory corruption.
Please see commit 94d0e5980d67.

Thanks,

        M.
-- 
Jazz is not dead. It just smells funny...

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