Re: [PATCH 02/20] KVM: arm64: Propagate host stage-2 annotated entries on block split

[Vincent Donnefort <vdonnefort@google.com>]

On Mon, Sep 07, 2026 at 02:58:41PM +0100, Wei-Lin Chang wrote:
> On Mon, Aug 03, 2026 at 11:08:46AM +0100, Vincent Donnefort wrote:
> 
> [...]
> 
> >  static void stage2_map_prefault_idmap(const struct kvm_pgtable_visit_ctx *ctx, kvm_pte_t *ptep)
> >  {
> >  	kvm_pte_t block_pte = ctx->old;
> > +	bool counted, valid;
> >  	u64 pa;
> >  	int i;
> >  
> > -	if (!kvm_pte_valid(block_pte))
> > +	counted = stage2_pte_is_counted(block_pte);
> > +	valid = kvm_pte_valid(block_pte);
> > +
> > +	if (!valid && !counted)
> > +		return;
> > +
> > +	/*
> > +	 * Shared walks not supported: cannot rollback refcounts on break
> > +	 * failure.
> > +	 */
> > +	if (counted && WARN_ON_ONCE(kvm_pgtable_walk_shared(ctx)))
> 
> Doesn't patch 1 also need this shared walk check,

Only the host stage-2 has the IDMAP flag and will run this function.

For the host stage-2, only non valid PTEs and non-RWX PTEs are refcounted.
  * non-valid PTEs are skipped in PATCH 1.
  * non-RWX PTEs are forced PTE-level.

So there's no risk of hitting a refcounted PTE in this function until PATCH 2.

-- 
Vincent

> 
> >  		return;
> >  
> >  	pa = ALIGN_DOWN(ctx->addr, kvm_granule_size(ctx->level));
> >  	for (i = 0; i < PTRS_PER_PTE; ++i, ++ptep, pa += kvm_granule_size(ctx->level + 1)) {
> > -		kvm_pte_t pte = kvm_init_valid_leaf_pte(pa, block_pte, ctx->level + 1);
> > +		kvm_pte_t pte = valid ?
> > +			kvm_init_valid_leaf_pte(pa, block_pte, ctx->level + 1) :
> > +			block_pte;
> >  
> >  		/*
> >  		 * Skip ptes in the range being modified by the caller if we're
> > @@ -1053,8 +1066,11 @@ static void stage2_map_prefault_idmap(const struct kvm_pgtable_visit_ctx *ctx, k
> >  		 * that should happen very infrequently.
> >  		 */
> >  		if ((ctx->level < (KVM_PGTABLE_LAST_LEVEL - 1)) ||
> > -		    (pa < ctx->addr) || (pa >= ctx->end))
> > +		    (pa < ctx->addr) || (pa >= ctx->end)) {
> >  			*ptep = pte;
> > +			if (counted)
> > +				ctx->mm_ops->get_page(ptep);
> 
> and this get_page() ?
> 
> Thanks,
> Wei-Lin Chang
> 
> [...]