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

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Message-ID: <CAAhSdy0QxZ7kfh34DO_mPuCbXUM6Use7XT-TSpayR1B3BEU3tg@mail.gmail.com>
Date:   Mon, 9 May 2022 11:04:32 +0530
From:   Anup Patel <anup@...infault.org>
To:     Atish Patra <atishp@...shpatra.org>
Cc:     Anup Patel <apatel@...tanamicro.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Alistair Francis <Alistair.Francis@....com>,
        KVM General <kvm@...r.kernel.org>,
        "open list:KERNEL VIRTUAL MACHINE FOR RISC-V (KVM/riscv)" 
        <kvm-riscv@...ts.infradead.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 7/7] RISC-V: KVM: Cleanup stale TLB entries when host
 CPU changes

On Fri, May 6, 2022 at 1:23 PM Atish Patra <atishp@...shpatra.org> wrote:
>
> On Wed, Apr 20, 2022 at 4:25 AM Anup Patel <apatel@...tanamicro.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@...tanamicro.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@...osinc.com>

Queued this patch for 5.19

Thanks,
Anup

> --
> Regards,
> Atish