linux-kernel - Re: [PATCH] mm, virt: merge AS_UNMOVABLE and AS

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: <f435d056-a611-41a8-a58f-7603f6475b1d@redhat.com>
Date: Thu, 11 Jul 2024 20:40:24 +0200
From: David Hildenbrand <david@...hat.com>
To: Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
 kvm@...r.kernel.org
Cc: vbabka@...e.cz, seanjc@...gle.com, michael.roth@....com,
 linux-mm@...ck.org
Subject: Re: [PATCH] mm, virt: merge AS_UNMOVABLE and AS_INACCESSIBLE

On 11.07.24 20:03, Paolo Bonzini wrote:
> The flags AS_UNMOVABLE and AS_INACCESSIBLE were both added just for guest_memfd;
> AS_UNMOVABLE is already in existing versions of Linux, while AS_INACCESSIBLE was
> acked for inclusion in 6.11.
> 
> But really, they are the same thing: only guest_memfd uses them, at least for
> now, and guest_memfd pages are unmovable because they should not be
> accessed by the CPU.
> 
> So merge them into one; use the AS_INACCESSIBLE name which is more comprehensive.
> At the same time, this fixes an embarrassing bug where AS_INACCESSIBLE was used
> as a bit mask, despite it being just a bit index.
> 
> The bug was mostly benign, becaus AS_INACCESSIBLE's bit representation (1010)
> corresponded to setting AS_UNEVICTABLE (which is already set) and AS_ENOSPC
> (except no async writes can happen on the guest_memfd).  So the AS_INACCESSIBLE
> flag simply had no effect.
> 
> Fixes: 1d23040caa8b ("KVM: guest_memfd: Use AS_INACCESSIBLE when creating guest_memfd inode")
> Fixes: c72ceafbd12c ("mm: Introduce AS_INACCESSIBLE for encrypted/confidential memory")
> Cc: linux-mm@...ck.org

Yeah, if we have to bring back the separation in the future, we can 
revisit that.

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb