linux-kernel - Re: [RFC PATCH 1/2] mm,drm/ttm: Block fast GUP to TTM huge pages

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 for Android: free password hash cracker in your pocket

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

Message-ID: <75423f64-adef-a2c4-8e7d-2cb814127b18@intel.com>
Date:   Wed, 24 Mar 2021 09:34:48 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Thomas Hellström (Intel) 
        <thomas_os@...pmail.org>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "christian.koenig@....com" <christian.koenig@....com>,
        "jgg@...dia.com" <jgg@...dia.com>,
        "airlied@...ux.ie" <airlied@...ux.ie>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH 1/2] mm,drm/ttm: Block fast GUP to TTM huge pages

On 3/24/21 3:05 AM, Thomas Hellström (Intel) wrote:
> Yes, I agree. Seems like the special (SW1) is available also for huge
> page table entries on x86 AFAICT, although just not implemented.
> Otherwise the SW bits appear completely used up.

Although the _PAGE_BIT_SOFTW* bits are used up, there's plenty of room
in the hardware PTEs.  Bits 52->58 are software-available, and we're
only using 58 at the moment.

We also have not been careful at *all* about how _PAGE_BIT_SOFTW* are
used.  It's quite possible we can encode another use even in the
existing bits.

Personally, I'd just try:

#define _PAGE_BIT_SOFTW5        57      /* available for programmer */