Re: [PATCH v2 7/7] RISC-V: KVM: Cleanup stale TLB entries when host CPU changes

[Atish Patra <atishp@atishpatra.org>]

On Wed, Apr 20, 2022 at 4:25 AM Anup Patel <apatel@ventanamicro.com> wrote:
>
> On RISC-V platforms with hardware VMID support, we share same
> VMID for all VCPUs of a particular Guest/VM. This means we might
> have stale G-stage TLB entries on the current Host CPU due to
> some other VCPU of the same Guest which ran previously on the
> current Host CPU.
>
> To cleanup stale TLB entries, we simply flush all G-stage TLB
> entries by VMID whenever underlying Host CPU changes for a VCPU.
>
> Signed-off-by: Anup Patel <apatel@ventanamicro.com>
> ---
>  arch/riscv/include/asm/kvm_host.h |  5 +++++
>  arch/riscv/kvm/tlb.c              | 23 +++++++++++++++++++++++
>  arch/riscv/kvm/vcpu.c             | 11 +++++++++++
>  3 files changed, 39 insertions(+)
>
> diff --git a/arch/riscv/include/asm/kvm_host.h b/arch/riscv/include/asm/kvm_host.h
> index a40e88a9481c..94349a5ffd34 100644
> --- a/arch/riscv/include/asm/kvm_host.h
> +++ b/arch/riscv/include/asm/kvm_host.h
> @@ -166,6 +166,9 @@ struct kvm_vcpu_arch {
>         /* VCPU ran at least once */
>         bool ran_atleast_once;
>
> +       /* Last Host CPU on which Guest VCPU exited */
> +       int last_exit_cpu;
> +
>         /* ISA feature bits (similar to MISA) */
>         unsigned long isa;
>
> @@ -256,6 +259,8 @@ void kvm_riscv_local_hfence_vvma_gva(unsigned long vmid,
>                                      unsigned long order);
>  void kvm_riscv_local_hfence_vvma_all(unsigned long vmid);
>
> +void kvm_riscv_local_tlb_sanitize(struct kvm_vcpu *vcpu);
> +
>  void kvm_riscv_fence_i_process(struct kvm_vcpu *vcpu);
>  void kvm_riscv_hfence_gvma_vmid_all_process(struct kvm_vcpu *vcpu);
>  void kvm_riscv_hfence_vvma_all_process(struct kvm_vcpu *vcpu);
> diff --git a/arch/riscv/kvm/tlb.c b/arch/riscv/kvm/tlb.c
> index c0f86d09c41d..1a76d0b1907d 100644
> --- a/arch/riscv/kvm/tlb.c
> +++ b/arch/riscv/kvm/tlb.c
> @@ -215,6 +215,29 @@ void kvm_riscv_local_hfence_vvma_all(unsigned long vmid)
>         csr_write(CSR_HGATP, hgatp);
>  }
>
> +void kvm_riscv_local_tlb_sanitize(struct kvm_vcpu *vcpu)
> +{
> +       unsigned long vmid;
> +
> +       if (!kvm_riscv_gstage_vmid_bits() ||
> +           vcpu->arch.last_exit_cpu == vcpu->cpu)
> +               return;
> +
> +       /*
> +        * On RISC-V platforms with hardware VMID support, we share same
> +        * VMID for all VCPUs of a particular Guest/VM. This means we might
> +        * have stale G-stage TLB entries on the current Host CPU due to
> +        * some other VCPU of the same Guest which ran previously on the
> +        * current Host CPU.
> +        *
> +        * To cleanup stale TLB entries, we simply flush all G-stage TLB
> +        * entries by VMID whenever underlying Host CPU changes for a VCPU.
> +        */
> +
> +       vmid = READ_ONCE(vcpu->kvm->arch.vmid.vmid);
> +       kvm_riscv_local_hfence_gvma_vmid_all(vmid);
> +}
> +
>  void kvm_riscv_fence_i_process(struct kvm_vcpu *vcpu)
>  {
>         local_flush_icache_all();
> diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
> index 9cd8f6e91c98..a86710fcd2e0 100644
> --- a/arch/riscv/kvm/vcpu.c
> +++ b/arch/riscv/kvm/vcpu.c
> @@ -67,6 +67,8 @@ static void kvm_riscv_reset_vcpu(struct kvm_vcpu *vcpu)
>         if (loaded)
>                 kvm_arch_vcpu_put(vcpu);
>
> +       vcpu->arch.last_exit_cpu = -1;
> +
>         memcpy(csr, reset_csr, sizeof(*csr));
>
>         memcpy(cntx, reset_cntx, sizeof(*cntx));
> @@ -735,6 +737,7 @@ static void noinstr kvm_riscv_vcpu_enter_exit(struct kvm_vcpu *vcpu)
>  {
>         guest_state_enter_irqoff();
>         __kvm_riscv_switch_to(&vcpu->arch);
> +       vcpu->arch.last_exit_cpu = vcpu->cpu;
>         guest_state_exit_irqoff();
>  }
>
> @@ -829,6 +832,14 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
>                         continue;
>                 }
>
> +               /*
> +                * Cleanup stale TLB enteries
> +                *
> +                * Note: This should be done after G-stage VMID has been
> +                * updated using kvm_riscv_gstage_vmid_ver_changed()
> +                */
> +               kvm_riscv_local_tlb_sanitize(vcpu);
> +
>                 guest_timing_enter_irqoff();
>
>                 kvm_riscv_vcpu_enter_exit(vcpu);
> --
> 2.25.1
>


Reviewed-by: Atish Patra <atishp@rivosinc.com>
-- 
Regards,
Atish