[PATCH v3] RISC-V: KVM: flush VS-stage TLB after VCPU migration to prevent stale entries

[Anup Patel]

On Thu, Oct 23, 2025 at 8:59 AM Hui Min Mina Chou
<minachou at andestech.com> wrote:
>
> From: Hui Min Mina Chou <minachou at andestech.com>
>
> If multiple VCPUs of the same Guest/VM run on the same Host CPU,
> hfence.vvma only flushes that Host CPU’s VS-stage TLB. Other Host CPUs
> may retain stale VS-stage entries. When a VCPU later migrates to a
> different Host CPU, it can hit these stale GVA to GPA mappings, causing
> unexpected faults in the Guest.
>
> To fix this, kvm_riscv_gstage_vmid_sanitize() is extended to flush both
> G-stage and VS-stage TLBs whenever a VCPU migrates to a different Host CPU.
> This ensures that no stale VS-stage mappings remain after VCPU migration.
>
> Fixes: 92e450507d56 ("RISC-V: KVM: Cleanup stale TLB entries when host CPU changes")
> Signed-off-by: Hui Min Mina Chou <minachou at andestech.com>
> Signed-off-by: Ben Zong-You Xie <ben717 at andestech.com>
> Reviewed-by: Radim Krčmář <rkrcmar at ventanamicro.com>

My comments on v2 are not addressed.

Regards,
Anup

> ---
> v3:
> - Resolved build warning; updated header declaration and call side to
>   kvm_riscv_local_tlb_sanitize
>
> v2:
> - Updated Fixes commit to 92e450507d56
> - Renamed function to kvm_riscv_local_tlb_sanitize
>
>  arch/riscv/include/asm/kvm_vmid.h | 2 +-
>  arch/riscv/kvm/vcpu.c             | 2 +-
>  arch/riscv/kvm/vmid.c             | 8 +++++++-
>  3 files changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/arch/riscv/include/asm/kvm_vmid.h b/arch/riscv/include/asm/kvm_vmid.h
> index ab98e1434fb7..75fb6e872ccd 100644
> --- a/arch/riscv/include/asm/kvm_vmid.h
> +++ b/arch/riscv/include/asm/kvm_vmid.h
> @@ -22,6 +22,6 @@ unsigned long kvm_riscv_gstage_vmid_bits(void);
>  int kvm_riscv_gstage_vmid_init(struct kvm *kvm);
>  bool kvm_riscv_gstage_vmid_ver_changed(struct kvm_vmid *vmid);
>  void kvm_riscv_gstage_vmid_update(struct kvm_vcpu *vcpu);
> -void kvm_riscv_gstage_vmid_sanitize(struct kvm_vcpu *vcpu);
> +void kvm_riscv_local_tlb_sanitize(struct kvm_vcpu *vcpu);
>
>  #endif
> diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
> index 3ebcfffaa978..796218e4a462 100644
> --- a/arch/riscv/kvm/vcpu.c
> +++ b/arch/riscv/kvm/vcpu.c
> @@ -968,7 +968,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
>                  * Note: This should be done after G-stage VMID has been
>                  * updated using kvm_riscv_gstage_vmid_ver_changed()
>                  */
> -               kvm_riscv_gstage_vmid_sanitize(vcpu);
> +               kvm_riscv_local_tlb_sanitize(vcpu);
>
>                 trace_kvm_entry(vcpu);
>
> diff --git a/arch/riscv/kvm/vmid.c b/arch/riscv/kvm/vmid.c
> index 3b426c800480..6323f5383d36 100644
> --- a/arch/riscv/kvm/vmid.c
> +++ b/arch/riscv/kvm/vmid.c
> @@ -125,7 +125,7 @@ void kvm_riscv_gstage_vmid_update(struct kvm_vcpu *vcpu)
>                 kvm_make_request(KVM_REQ_UPDATE_HGATP, v);
>  }
>
> -void kvm_riscv_gstage_vmid_sanitize(struct kvm_vcpu *vcpu)
> +void kvm_riscv_local_tlb_sanitize(struct kvm_vcpu *vcpu)
>  {
>         unsigned long vmid;
>
> @@ -146,4 +146,10 @@ void kvm_riscv_gstage_vmid_sanitize(struct kvm_vcpu *vcpu)
>
>         vmid = READ_ONCE(vcpu->kvm->arch.vmid.vmid);
>         kvm_riscv_local_hfence_gvma_vmid_all(vmid);
> +
> +       /*
> +        * Flush VS-stage TLBs entry after VCPU migration to avoid using
> +        * stale entries.
> +        */
> +       kvm_riscv_local_hfence_vvma_all(vmid);
>  }
> --
> 2.34.1
>