Re: [PATCH v2 4/8] KVM: arm64: Correctly handle end of VA space TLBI invalidation

Hi Marc,

On Thu, Aug 06, 2026 at 10:10:22AM +0100, Marc Zyngier wrote:
> Our TLB invalidation by VA code is based on comparing two ranges,
> one defined by the TLB, and one defined by the TLBI instruction.
> 
> Each range is defined by a start and a size. However, the way the
> comparison is done doesn't account for address rollover, as it
> compares an address with (base + size). This works nicely until
> this expression represent the last page/block in the TTBR1 VA space,
> as the result is a big fat 0. And a failed TLB invalidation.
> 
> Rewrite the comparison in a way that is immune to the address
> rollover (making the end address inclusive instead of exclusive),
> and move this into a common helper that is used by both VA and IPA
> invalidations, as suggested by Hyunwoo Kim (although the IPA version
> didn't suffer from this particular problem, obviously).
> 
> Fixes: 4ffa72ad8f37e ("KVM: arm64: nv: Add S1 TLB invalidation primitive for VNCR_EL2")
> Reviewed-by: Yuan Yao <[email protected]>
> Signed-off-by: Marc Zyngier <[email protected]>
> Cc: [email protected]
> ---
>  arch/arm64/kvm/nested.c | 43 ++++++++++++++++++-----------------------
>  1 file changed, 19 insertions(+), 24 deletions(-)
> 
> diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
> index 27bc7ee4b3382..8a602d074dbb4 100644
> --- a/arch/arm64/kvm/nested.c
> +++ b/arch/arm64/kvm/nested.c
> @@ -999,6 +999,20 @@ static void invalidate_vncr(struct vncr_tlb *vt)
>  		clear_fixmap(vncr_fixmap(vt->cpu));
>  }
>  
> +static bool vncr_tlb_intersects(struct vncr_tlb *vt, u64 addr,
> +				u64 scope_start, u64 scope_size)
> +{
> +	u64 tlb_size, tlb_start, tlb_end, scope_end;
> +
> +	tlb_size = ttl_to_size(pgshift_level_to_ttl(vt->wi.pgshift, vt->wr.level));
> +
> +	tlb_start = addr & ~(tlb_size - 1);
> +	tlb_end = tlb_start + tlb_size - 1;
> +	scope_end = scope_start + scope_size - 1;

I think if scope_end overflows,

> +
> +	return !(tlb_end < scope_start || tlb_start > scope_end);

tlb_start > scope_end can evaluate to true and we return false even when
there is overlap near the end of the TTBR1 address space.

Therefore I think we need to saturate scope_end to ULONG_MAX when overflow
happens. This is also what the architecture does when looking at the
pseudocode J1.2.3.442 TLBIRange (M.c).

Thanks,
Wei-Lin Chang

> +}
> +
>  /*
>   * VNCR TLB invalidation occurs from MMU notifiers or TLBI instructions, and
>   * either can race against a vcpu not being onlined yet (no pseudo-TLB
> @@ -1021,19 +1035,9 @@ 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_vncr_tlb(i, vcpu, vt, kvm) {
> -		u64 ipa_start, ipa_end, ipa_size;
> -
> -		ipa_size = ttl_to_size(pgshift_level_to_ttl(vt->wi.pgshift,
> -							    vt->wr.level));
> -		ipa_start = vt->wr.pa & ~(ipa_size - 1);
> -		ipa_end = ipa_start + ipa_size;
> -
> -		if (ipa_end <= start || ipa_start >= end)
> -			continue;
> -
> -		invalidate_vncr(vt);
> -	}
> +	kvm_for_each_vncr_tlb(i, vcpu, vt, kvm)
> +		if (vncr_tlb_intersects(vt, vt->wr.pa, start, end - start))
> +			invalidate_vncr(vt);
>  }
>  
>  struct s1e2_tlbi_scope {
> @@ -1059,28 +1063,19 @@ static void invalidate_vncr_va(struct kvm *kvm,
>  	lockdep_assert_held_write(&kvm->mmu_lock);
>  
>  	kvm_for_each_vncr_tlb(i, vcpu, vt, kvm) {
> -		u64 va_start, va_end, va_size;
> -
> -		va_size = ttl_to_size(pgshift_level_to_ttl(vt->wi.pgshift,
> -							   vt->wr.level));
> -		va_start = vt->gva & ~(va_size - 1);
> -		va_end = va_start + va_size;
> -
>  		switch (scope->type) {
>  		case TLBI_ALL:
>  			break;
>  
>  		case TLBI_VA:
> -			if (va_end <= scope->va ||
> -			    va_start >= (scope->va + scope->size))
> +			if (!vncr_tlb_intersects(vt, vt->gva, scope->va, scope->size))
>  				continue;
>  			if (vt->wr.nG && vt->wr.asid != scope->asid)
>  				continue;
>  			break;
>  
>  		case TLBI_VAA:
> -			if (va_end <= scope->va ||
> -			    va_start >= (scope->va + scope->size))
> +			if (!vncr_tlb_intersects(vt, vt->gva, scope->va, scope->size))
>  				continue;
>  			break;
>  
> -- 
> 2.47.3
>