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

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Message-ID: <20250214192704.GD3696814@ziepe.ca>
Date: Fri, 14 Feb 2025 15:27:04 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: Alex Williamson <alex.williamson@...hat.com>
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 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;

?

> +				ret = min_t(int, npages, epfn - *pfn);

It is nitty but the int's here should be long, and npages should be
unsigned long..

Jason