linux-kernel - Re: [PATCH 5/5] vfio/type1: Use mapping page mask for pfnmaps

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Message-ID: <20250217145221.20f17b7a.alex.williamson@redhat.com>
Date: Mon, 17 Feb 2025 14:52:21 -0700
From: Alex Williamson <alex.williamson@...hat.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, peterx@...hat.com,
 mitchell.augustin@...onical.com, clg@...hat.com, akpm@...ux-foundation.org,
 linux-mm@...ck.org
Subject: Re: [PATCH 5/5] vfio/type1: Use mapping page mask for pfnmaps

On Fri, 14 Feb 2025 15:27:04 -0400
Jason Gunthorpe <jgg@...pe.ca> wrote:

> On Wed, Feb 05, 2025 at 04:17:21PM -0700, Alex Williamson wrote:
> > @@ -590,15 +592,23 @@ static int vaddr_get_pfns(struct mm_struct *mm, unsigned long vaddr,
> >  	vma = vma_lookup(mm, vaddr);
> >  
> >  	if (vma && vma->vm_flags & VM_PFNMAP) {
> > -		ret = follow_fault_pfn(vma, mm, vaddr, pfn, prot & IOMMU_WRITE);
> > +		unsigned long pgmask;
> > +
> > +		ret = follow_fault_pfn(vma, mm, vaddr, pfn, &pgmask,
> > +				       prot & IOMMU_WRITE);
> >  		if (ret == -EAGAIN)
> >  			goto retry;
> >  
> >  		if (!ret) {
> > -			if (is_invalid_reserved_pfn(*pfn))
> > -				ret = 1;
> > -			else
> > +			if (is_invalid_reserved_pfn(*pfn)) {
> > +				unsigned long epfn;
> > +
> > +				epfn = (((*pfn << PAGE_SHIFT) + ~pgmask + 1)
> > +					& pgmask) >> PAGE_SHIFT;  
> 
> That seems a bit indirect
> 
>  epfn = ((*pfn) | (~pgmask >> PAGE_SHIFT)) + 1;
> 
> ?

That is simpler, for sure.  Thanks!

> > +				ret = min_t(int, npages, epfn - *pfn);  
> 
> It is nitty but the int's here should be long, and npages should be
> unsigned long..

Added a new patch that uses unsigned long consistently for passed page
counts and long for returns.  Now we just need a system with a 16TiB
huge page size.  Thanks,

Alex