Re: [PATCH] riscv: kvm: mmu: fix unlocked gstage unmap in kvm_unmap_gfn_range

On Thu, Apr 16, 2026 at 2:49 PM cuitao <[email protected]> wrote:
>
> When spin_trylock fails in kvm_unmap_gfn_range(), the code still
> proceeds to call kvm_riscv_gstage_unmap_range() without holding
> kvm->mmu_lock, which races with concurrent page table modifications.
>
> Skip the unmap and return false on trylock failure so the MMU notifier
> will flush and retry, matching the pattern used by other architectures.
>
> Signed-off-by: cuitao <[email protected]>

We will be using mmu_lock as rwlock.
(Refer, https://patchwork.ozlabs.org/project/kvm-riscv/patch/[email protected]/)

Regards,
Anup

> ---
>  arch/riscv/kvm/mmu.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/riscv/kvm/mmu.c b/arch/riscv/kvm/mmu.c
> index 088d33ba90ed..d37cc717fdaf 100644
> --- a/arch/riscv/kvm/mmu.c
> +++ b/arch/riscv/kvm/mmu.c
> @@ -245,7 +245,6 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
>  bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
>  {
>         struct kvm_gstage gstage;
> -       bool mmu_locked;
>
>         if (!kvm->arch.pgd)
>                 return false;
> @@ -254,12 +253,13 @@ bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
>         gstage.flags = 0;
>         gstage.vmid = READ_ONCE(kvm->arch.vmid.vmid);
>         gstage.pgd = kvm->arch.pgd;
> -       mmu_locked = spin_trylock(&kvm->mmu_lock);
> +       if (!spin_trylock(&kvm->mmu_lock))
> +               return false;
> +
>         kvm_riscv_gstage_unmap_range(&gstage, range->start << PAGE_SHIFT,
>                                      (range->end - range->start) << PAGE_SHIFT,
>                                      range->may_block);
> -       if (mmu_locked)
> -               spin_unlock(&kvm->mmu_lock);
> +       spin_unlock(&kvm->mmu_lock);
>         return false;
>  }
>
> --
> 2.43.0
>

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