linux-kernel - Re: [GIT PULL] VFIO updates for v6.17-rc1

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Message-ID: <57582464-cfd5-47f5-877d-88918ffa2ec0@redhat.com>
Date: Tue, 5 Aug 2025 16:22:32 +0200
From: David Hildenbrand <david@...hat.com>
To: Jason Gunthorpe <jgg@...dia.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
 Alex Williamson <alex.williamson@...hat.com>,
 "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "lizhe.67@...edance.com" <lizhe.67@...edance.com>
Subject: Re: [GIT PULL] VFIO updates for v6.17-rc1

On 05.08.25 16:20, Jason Gunthorpe wrote:
> On Tue, Aug 05, 2025 at 04:10:45PM +0200, David Hildenbrand wrote:
>> There are some weird scenarios where you hotplug memory after boot memory,
>> and suddenly you can runtime-allocate a gigantic folio that spans both
>> ranges etc.
> 
> I was thinking we'd forbid this directly, but yes it is a another new
> check.
> 
>> So while related, the corner cases are all a bit nasty, and just forbidding
>> folios to span a memory section on these problematic configs (sparse
>> !vmemmap) sounds interesting.
> 
> Indeed, this just sounds like forcing MAX_ORDER to be no larger than
> the section size for this old mode?

MAX_ORDER is always limited to the section size already.

MAX_ORDER is only about buddy allocations. What hugetlb and dax do is 
independent of MAX_ORDER.

-- 
Cheers,

David / dhildenb