Re: [PATCH v6 11/38] KVM: x86: hyper-v: Create a separate fifo for L2 TLB flush

[Maxim Levitsky <mlevitsk@redhat.com>]

On Mon, 2022-06-06 at 10:36 +0200, Vitaly Kuznetsov wrote:
> To handle L2 TLB flush requests, KVM needs to use a separate fifo from
> regular (L1) Hyper-V TLB flush requests: e.g. when a request to flush
> something in L2 is made, the target vCPU can transition from L2 to L1,
> receive a request to flush a GVA for L1 and then try to enter L2 back.
> The first request needs to be processed at this point. Similarly,
> requests to flush GVAs in L1 must wait until L2 exits to L1.
> 
> No functional change as KVM doesn't handle L2 TLB flush requests from
> L2 yet.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
>  arch/x86/include/asm/kvm_host.h |  8 +++++++-
>  arch/x86/kvm/hyperv.c           | 11 +++++++----
>  arch/x86/kvm/hyperv.h           | 17 ++++++++++++++---
>  3 files changed, 28 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index cf3748be236d..0e58ab00dff0 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -613,6 +613,12 @@ struct kvm_vcpu_hv_synic {
>   */
>  #define KVM_HV_TLB_FLUSHALL_ENTRY  ((u64)-1)
>  
> +enum hv_tlb_flush_fifos {
> +       HV_L1_TLB_FLUSH_FIFO,
> +       HV_L2_TLB_FLUSH_FIFO,
> +       HV_NR_TLB_FLUSH_FIFOS,
> +};
> +
>  struct kvm_vcpu_hv_tlb_flush_fifo {
>         spinlock_t write_lock;
>         DECLARE_KFIFO(entries, u64, KVM_HV_TLB_FLUSH_FIFO_SIZE);
> @@ -638,7 +644,7 @@ struct kvm_vcpu_hv {
>                 u32 syndbg_cap_eax; /* HYPERV_CPUID_SYNDBG_PLATFORM_CAPABILITIES.EAX */
>         } cpuid_cache;
>  
> -       struct kvm_vcpu_hv_tlb_flush_fifo tlb_flush_fifo;
> +       struct kvm_vcpu_hv_tlb_flush_fifo tlb_flush_fifo[HV_NR_TLB_FLUSH_FIFOS];
>  };
>  
>  /* Xen HVM per vcpu emulation context */
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index b347971b3924..32f223bbea6b 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -956,8 +956,10 @@ static int kvm_hv_vcpu_init(struct kvm_vcpu *vcpu)
>  
>         hv_vcpu->vp_index = vcpu->vcpu_idx;
>  
> -       INIT_KFIFO(hv_vcpu->tlb_flush_fifo.entries);
> -       spin_lock_init(&hv_vcpu->tlb_flush_fifo.write_lock);
> +       for (i = 0; i < HV_NR_TLB_FLUSH_FIFOS; i++) {
> +               INIT_KFIFO(hv_vcpu->tlb_flush_fifo[i].entries);
> +               spin_lock_init(&hv_vcpu->tlb_flush_fifo[i].write_lock);
> +       }
>  
>         return 0;
>  }
> @@ -1843,7 +1845,8 @@ static void hv_tlb_flush_enqueue(struct kvm_vcpu *vcpu, u64 *entries, int count)
>         if (!hv_vcpu)
>                 return;
>  
> -       tlb_flush_fifo = &hv_vcpu->tlb_flush_fifo;
> +       /* kvm_hv_flush_tlb() is not ready to handle requests for L2s yet */
> +       tlb_flush_fifo = &hv_vcpu->tlb_flush_fifo[HV_L1_TLB_FLUSH_FIFO];
Yes, as expected here the local var starts to make sense.
>  
>         spin_lock_irqsave(&tlb_flush_fifo->write_lock, flags);
>  
> @@ -1880,7 +1883,7 @@ void kvm_hv_vcpu_flush_tlb(struct kvm_vcpu *vcpu)
>                 return;
>         }
>  
> -       tlb_flush_fifo = &hv_vcpu->tlb_flush_fifo;
> +       tlb_flush_fifo = kvm_hv_get_tlb_flush_fifo(vcpu);
>  
>         count = kfifo_out(&tlb_flush_fifo->entries, entries, KVM_HV_TLB_FLUSH_FIFO_SIZE);
>  
> diff --git a/arch/x86/kvm/hyperv.h b/arch/x86/kvm/hyperv.h
> index e5b32266ff7d..207d24efdc5a 100644
> --- a/arch/x86/kvm/hyperv.h
> +++ b/arch/x86/kvm/hyperv.h
> @@ -22,6 +22,7 @@
>  #define __ARCH_X86_KVM_HYPERV_H__
>  
>  #include <linux/kvm_host.h>
> +#include "x86.h"
>  
>  /*
>   * The #defines related to the synthetic debugger are required by KDNet, but
> @@ -147,16 +148,26 @@ int kvm_vm_ioctl_hv_eventfd(struct kvm *kvm, struct kvm_hyperv_eventfd *args);
>  int kvm_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid,
>                      struct kvm_cpuid_entry2 __user *entries);
>  
> +static inline struct kvm_vcpu_hv_tlb_flush_fifo *kvm_hv_get_tlb_flush_fifo(struct kvm_vcpu *vcpu)
> +{
> +       struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
> +       int i = !is_guest_mode(vcpu) ? HV_L1_TLB_FLUSH_FIFO :
> +                                      HV_L2_TLB_FLUSH_FIFO;
> +
> +       /* KVM does not handle L2 TLB flush requests yet */
> +       WARN_ON_ONCE(i != HV_L1_TLB_FLUSH_FIFO);
> +
> +       return &hv_vcpu->tlb_flush_fifo[i];
> +}
>  
>  static inline void kvm_hv_vcpu_empty_flush_tlb(struct kvm_vcpu *vcpu)
>  {
>         struct kvm_vcpu_hv_tlb_flush_fifo *tlb_flush_fifo;
> -       struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
>  
> -       if (!hv_vcpu || !kvm_check_request(KVM_REQ_HV_TLB_FLUSH, vcpu))
> +       if (!to_hv_vcpu(vcpu) || !kvm_check_request(KVM_REQ_HV_TLB_FLUSH, vcpu))
>                 return;
>  
> -       tlb_flush_fifo = &hv_vcpu->tlb_flush_fifo;
> +       tlb_flush_fifo = kvm_hv_get_tlb_flush_fifo(vcpu);
>  
>         kfifo_reset_out(&tlb_flush_fifo->entries);
>  }


Looks great,

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>

Best regards,
	Maxim Levitsky