Re: [PATCH v2 3/9] KVM: arm64: Add a range to __pkvm_host_unshare_guest()

[Vincent Donnefort]

On Thu, Apr 03, 2025 at 03:31:47PM +0000, Quentin Perret wrote:
> On Thursday 06 Mar 2025 at 11:00:32 (+0000), Vincent Donnefort wrote:
> > @@ -1012,51 +1011,52 @@ static int __check_host_shared_guest(struct pkvm_hyp_vm *vm, u64 *__phys, u64 ip
> >  		return ret;
> >  	if (!kvm_pte_valid(pte))
> >  		return -ENOENT;
> > -	if (level != KVM_PGTABLE_LAST_LEVEL)
> > +	if (kvm_granule_size(level) != size)
> >  		return -E2BIG;
> >  
> > -	state = guest_get_page_state(pte, ipa);
> > -	if (state != PKVM_PAGE_SHARED_BORROWED)
> > -		return -EPERM;
> > +	ret = __guest_check_page_state_range(vm, ipa, size, PKVM_PAGE_SHARED_BORROWED);
> > +	if (ret)
> > +		return ret;
> 
> Given that hard rely on kvm_granule_size(level) == size above, we should
> be guaranteed that the PTE covers the entire range we're interested in.
> So is there a point in starting a new page-table walk here? Could we
> just keep guest_get_page_state() directly?

Ha yes, the walk wouldn't do anything more than what we can with that PTE!

> 
> >  
> >  	phys = kvm_pte_to_phys(pte);
> > -	ret = check_range_allowed_memory(phys, phys + PAGE_SIZE);
> > +	ret = check_range_allowed_memory(phys, phys + size);
> >  	if (WARN_ON(ret))
> >  		return ret;
> >  
> > -	page = hyp_phys_to_page(phys);
> > -	if (page->host_state != PKVM_PAGE_SHARED_OWNED)
> > -		return -EPERM;
> > -	if (WARN_ON(!page->host_share_guest_count))
> > -		return -EINVAL;
> > +	for_each_hyp_page(phys, size, page) {
> > +		if (page->host_state != PKVM_PAGE_SHARED_OWNED)
> > +			return -EPERM;
> > +		if (WARN_ON(!page->host_share_guest_count))
> > +			return -EINVAL;
> > +	}
> >  
> >  	*__phys = phys;
> >  
> >  	return 0;
> >  }