Re: [PATCH v3 08/15] KVM: WARN and reject guest-based uaccess if VM is dying

[James Houghton]

On Tue, Oct 27, 2026 at 3:12 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
>
> WARN and reject user accesses to guest memory if the associated VM is dying
> even if the current address space happens to be the correct address space.
> Accessing guest memory after the last reference to the VM has been put may
> be "fine" from a safety perspective, but it's still a KVM bug.
>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>

Reviewed-by: James Houghton <jthoughton@xxxxxxxxxx>

> ---
>  include/linux/kvm_host.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index f3f59bdf7e18..ba8ea62b7304 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -1355,7 +1355,8 @@ int kvm_gfn_to_hva_cache_init(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
>
>  static __always_inline __must_check bool kvm_can_do_uaccess(struct kvm *kvm)
>  {
> -       return !WARN_ON_ONCE(current->mm != kvm->mm);
> +       return !WARN_ON_ONCE(current->mm != kvm->mm ||
> +                            !refcount_read(&kvm->users_count));
>  }
>
>  #define BUILD_KVM_COPY_USER_WRAPPER(fn, to_user, from_user)                            \
> --
> 2.56.0.307.g5fe7bd680c-goog
>