linux-kernel - RE: [PATCH] Revert "vfio/type1: Unpin zero pages"

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Date: Mon, 4 Mar 2024 08:06:02 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Alex Williamson <alex.williamson@...hat.com>
CC: "david@...hat.com" <david@...hat.com>, "kvm@...r.kernel.org"
	<kvm@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] Revert "vfio/type1: Unpin zero pages"

> From: Alex Williamson <alex.williamson@...hat.com>
> Sent: Friday, March 1, 2024 6:36 AM
> 
> This reverts commit 873aefb376bbc0ed1dd2381ea1d6ec88106fdbd4.
> 
> This was a heinous workaround and it turns out it's been fixed in mm
> twice since it was introduced.  Most recently, commit c8070b787519
> ("mm: Don't pin ZERO_PAGE in pin_user_pages()") would have prevented
> running up the zeropage refcount, but even before that commit
> 84209e87c696 ("mm/gup: reliable R/O long-term pinning in COW mappings")
> avoids the vfio use case from pinning the zeropage at all, instead
> replacing it with exclusive anonymous pages.
> 
> Remove this now useless overhead.
> 
> Suggested-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: Alex Williamson <alex.williamson@...hat.com>

Reviewed-by: Kevin Tian <kevin.tian@...el.com>