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Date: Wed, 29 Jan 2020 18:07:14 +0100
From: Christian Borntraeger <>
To: Christopher Lameter <>, Kees Cook <>
Cc: Jiri Slaby <>, Julian Wiedmann <>,
        Ursula Braun <>,
        Alexander Viro
 <>,, David Windsor <>,
        Pekka Enberg <>,
        David Rientjes <>,
        Joonsoo Kim <>,
        Andrew Morton <>,,,
        Linus Torvalds <>,
        Andy Lutomirski <>,
        Christoph Hellwig <>,
        "David S. Miller" <>,
        Laura Abbott <>, Mark Rutland <>,
        "Martin K. Petersen" <>,
        Paolo Bonzini <>,
        Christoffer Dall <>,
        Dave Kleikamp <>, Jan Kara <>,
        Luis de Bethencourt <>,
        Marc Zyngier
 <>, Rik van Riel <>,
        Matthew Garrett <>,,,,, Vlastimil Babka <>,
        Michal Kubecek <>
Subject: Re: [PATCH 09/38] usercopy: Mark kmalloc caches as
 usercopy caches

On 29.01.20 17:43, Christopher Lameter wrote:
> On Tue, 28 Jan 2020, Kees Cook wrote:
>>> On the other hand not marking the DMA caches still seems questionable.
>> My understanding is that exposing DMA memory to userspace copies can
>> lead to unexpected results, especially for misbehaving hardware, so I'm
>> not convinced this is a generically bad hardening choice.
> "DMA" memory (and thus DMA caches) have nothing to do with DMA. Its a
> legacy term. "DMA Memory" is memory limited to a certain
> physical address boundary (old restrictions on certain devices only
> supporting a limited number of address bits).
> DMA can be done to NORMAL memory as well.

I think iucv uses GFP_DMA because z/VM needs those buffers to reside below 2GB (which is ZONA_DMA for s390).

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