linux-kernel - Re: [PATCH v2 1/1] vfio/type1: Respect IOMMU reserved regions in vfio_test_domain

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Date:   Fri, 6 Jan 2023 14:03:42 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     Niklas Schnelle <schnelle@...ux.ibm.com>,
        Cornelia Huck <cohuck@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        Pierre Morel <pmorel@...ux.ibm.com>,
        Christian Bornträger <borntraeger@...ux.ibm.com>
Subject: Re: [PATCH v2 1/1] vfio/type1: Respect IOMMU reserved regions in
 vfio_test_domain_fgsp()

On Fri, Jan 06, 2023 at 10:24:50AM -0700, Alex Williamson wrote:

> > -	ret = iommu_map(domain->domain, 0, page_to_phys(pages), PAGE_SIZE * 2,
> > -			IOMMU_READ | IOMMU_WRITE | IOMMU_CACHE);
> > -	if (!ret) {
> > -		size_t unmapped = iommu_unmap(domain->domain, 0, PAGE_SIZE);
> > +	list_for_each_entry(region, regions, list) {
> > +		if (region->end - region->start < PAGE_SIZE * 2 ||
> > +				region->start % (PAGE_SIZE*2))
> 
> Maybe this falls into the noise, but we don't care if region->start is
> aligned to a double page, so long as we can map an aligned double page
> within the region.  Maybe something like:

> 	dma_addr_t start = ALIGN(region->start, PAGE_SIZE * 2);
> 
> 	if (start >= region->end || (region->end - start < PAGE_SIZE * 2))
> 		continue;

Yeah, that is more technically correct

Jason