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

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Message-ID: <Z6-djlOXYTDU12mc@casper.infradead.org>
Date: Fri, 14 Feb 2025 19:46:22 +0000
From: Matthew Wilcox <willy@...radead.org>
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:
> +			if (is_invalid_reserved_pfn(*pfn)) {
> +				unsigned long epfn;
> +
> +				epfn = (((*pfn << PAGE_SHIFT) + ~pgmask + 1)
> +					& pgmask) >> PAGE_SHIFT;
> +				ret = min_t(int, npages, epfn - *pfn);

You've really made life hard for yourself by passing around a page mask
instead of an order (ie 0/PMD_ORDER/PUD_ORDER).  Why not:

				epfn = round_up(*pfn + 1, 1 << order);

Although if you insist on passing around a mask, this could be:

				unsigned long sz = (~pgmask >> PAGE_SHIFT) + 1;
				unsigned long epfn = round_up(*pfn + 1, sz)