linux-kernel - Re: [PATCH 5/5] vfio-pci: Best-effort huge pfnmaps with !MAP

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250616230011.GS1174925@nvidia.com>
Date: Mon, 16 Jun 2025 20:00:11 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Peter Xu <peterx@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, kvm@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alex Williamson <alex.williamson@...hat.com>,
	Zi Yan <ziy@...dia.com>, Alex Mastro <amastro@...com>,
	David Hildenbrand <david@...hat.com>,
	Nico Pache <npache@...hat.com>
Subject: Re: [PATCH 5/5] vfio-pci: Best-effort huge pfnmaps with !MAP_FIXED
 mappings

On Mon, Jun 16, 2025 at 06:06:23PM -0400, Peter Xu wrote:

> Can I understand it as a suggestion to pass in a bitmask into the core mm
> API (e.g. keep the name of mm_get_unmapped_area_aligned()), instead of a
> constant "align", so that core mm would try to allocate from the largest
> size to smaller until it finds some working VA to use?

I don't think you need a bitmask.

Split the concerns, the caller knows what is inside it's FD. It only
needs to provide the highest pgoff aligned folio/pfn within the FD.

The mm knows what leaf page tables options exist. It should try to
align to the closest leaf page table size that is <= the FD's max
aligned folio.

Higher alignment would be wasteful of address space.

Lower alignment misses an opportunity to create large leaf PTEs.

Jason