Re: [PATCH] KVM: arm64: nv: Skip vCPUs without a pseudo-TLB in invalidate_vncr_va()

[Hyunwoo Kim <imv4bel@gmail.com>]

On Sun, Jun 07, 2026 at 02:05:02PM +0100, Marc Zyngier wrote:
> On Sun, 07 Jun 2026 09:43:53 +0100,
> Hyunwoo Kim <imv4bel@gmail.com> wrote:
> > 
> > vncr_tlb is not allocated before a vCPU runs for the first time, so
> > vcpu->arch.vncr_tlb is NULL for a vCPU that has been created but not yet
> > run. Code that iterates over every vCPU's pseudo-TLB must skip those.
> > 
> > invalidate_vncr_va() iterates over the vCPUs with kvm_for_each_vcpu() and
> > dereferences vt->valid without checking whether vncr_tlb is NULL.
> > 
> > While iterating, skip vCPUs whose pseudo-TLB has not been allocated.
> >
> > Fixes: 4ffa72ad8f37 ("KVM: arm64: nv: Add S1 TLB invalidation primitive for VNCR_EL2")
> > Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
> > ---
> >  arch/arm64/kvm/nested.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
> > index 6f7bc9a9992e..063e079d1d1a 100644
> > --- a/arch/arm64/kvm/nested.c
> > +++ b/arch/arm64/kvm/nested.c
> > @@ -969,6 +969,10 @@ static void invalidate_vncr_va(struct kvm *kvm,
> >  		struct vncr_tlb *vt = vcpu->arch.vncr_tlb;
> >  		u64 va_start, va_end, va_size;
> >  
> > +		/* Skip vCPUs whose pseudo-TLB hasn't been allocated yet */
> > +		if (!vt)
> > +			continue;
> > +
> >  		if (!vt->valid)
> >  			continue;
> >  
> 
> This looks correct and matches what we already have for
> invalidate_vncr_ipa().
> 
> But I think this misses the opportunity to squash a whole class of
> similar bugs, should we ever have the need for another function that
> iterates over all *valid* VNCR pseudo-TLBs.
> 
> Since I'm on a train and have nothing better to do, I've written the
> following hack.
> 
> Thoughts?

Looks like a good direction to me. I confirmed it fixes the issue (as
expected).

How about you submit this patch yourself?

> 
> 	M.
> 
> diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
> index 38f672e940878..f0a9f81a08302 100644
> --- a/arch/arm64/kvm/nested.c
> +++ b/arch/arm64/kvm/nested.c
> @@ -897,9 +897,21 @@ static void invalidate_vncr(struct vncr_tlb *vt)
>  		clear_fixmap(vncr_fixmap(vt->cpu));
>  }
>  
> +/*
> + * VNCR TLB invalidation occurs from MMU notifiers or TLBI instructions, and
> + * either can race against a vcpu not being onlined yet (no pseudo-TLB
> + * allocated). Similarly, the TLB might be invalid.  Skip those, as they
> + * obviously don't participate in the invalidation at this stage.
> + */
> +#define kvm_for_each_vncr_tlb(idx, vcpup, tlbp, kvm)	\
> +	kvm_for_each_vcpu(idx, vcpu, kvm)		\

Maybe vcpu -> vcpup?

> +		if (((tlbp) = vcpu->arch.vncr_tlb) &&	\
> +		    (tlbp)->valid)
> +
>  static void kvm_invalidate_vncr_ipa(struct kvm *kvm, u64 start, u64 end)
>  {
>  	struct kvm_vcpu *vcpu;
> +	struct vncr_tlb *vt;
>  	unsigned long i;
>  
>  	lockdep_assert_held_write(&kvm->mmu_lock);
> @@ -907,24 +919,9 @@ static void kvm_invalidate_vncr_ipa(struct kvm *kvm, u64 start, u64 end)
>  	if (!kvm_has_feat(kvm, ID_AA64MMFR4_EL1, NV_frac, NV2_ONLY))
>  		return;
>  
> -	kvm_for_each_vcpu(i, vcpu, kvm) {
> -		struct vncr_tlb *vt = vcpu->arch.vncr_tlb;
> +	kvm_for_each_vncr_tlb(i, vcpu, vt, kvm) {
>  		u64 ipa_start, ipa_end, ipa_size;
>  
> -		/*
> -		 * Careful here: We end-up here from an MMU notifier,
> -		 * and this can race against a vcpu not being onlined
> -		 * yet, without the pseudo-TLB being allocated.
> -		 *
> -		 * Skip those, as they obviously don't participate in
> -		 * the invalidation at this stage.
> -		 */
> -		if (!vt)
> -			continue;
> -
> -		if (!vt->valid)
> -			continue;
> -
>  		ipa_size = ttl_to_size(pgshift_level_to_ttl(vt->wi.pgshift,
>  							    vt->wr.level));
>  		ipa_start = vt->wr.pa & ~(ipa_size - 1);
> @@ -954,17 +951,14 @@ static void invalidate_vncr_va(struct kvm *kvm,
>  			       struct s1e2_tlbi_scope *scope)
>  {
>  	struct kvm_vcpu *vcpu;
> +	struct vncr_tlb *vt;
>  	unsigned long i;
>  
>  	lockdep_assert_held_write(&kvm->mmu_lock);
>  
> -	kvm_for_each_vcpu(i, vcpu, kvm) {
> -		struct vncr_tlb *vt = vcpu->arch.vncr_tlb;
> +	kvm_for_each_vncr_tlb(i, vcpu, vt, kvm) {
>  		u64 va_start, va_end, va_size;
>  
> -		if (!vt->valid)
> -			continue;
> -
>  		va_size = ttl_to_size(pgshift_level_to_ttl(vt->wi.pgshift,
>  							   vt->wr.level));
>  		va_start = vt->gva & ~(va_size - 1);
> 
> -- 
> Jazz isn't dead. It just smells funny.


Best regards,
Hyunwoo Kim