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Message-Id: <771c5511-c5ab-3dd1-d938-5dbc40396daa@de.ibm.com>
Date: Wed, 29 Jan 2020 18:19:56 +0100
From: Christian Borntraeger <borntraeger@...ibm.com>
To: Christoph Hellwig <hch@...radead.org>
Cc: Christopher Lameter <cl@...ux.com>, Kees Cook <keescook@...omium.org>,
Jiri Slaby <jslaby@...e.cz>, Julian Wiedmann <jwi@...ux.ibm.com>,
Ursula Braun <ubraun@...ux.ibm.com>,
Alexander Viro
<viro@...iv.linux.org.uk>,
linux-kernel@...r.kernel.org, David Windsor <dave@...lcore.net>,
Pekka Enberg <penberg@...nel.org>,
David Rientjes <rientjes@...gle.com>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
linux-xfs@...r.kernel.org,
Linus Torvalds <torvalds@...ux-foundation.org>,
Andy Lutomirski <luto@...nel.org>,
"David S. Miller" <davem@...emloft.net>,
Laura Abbott <labbott@...hat.com>, Mark Rutland <mark.rutland@....com>,
"Martin K. Petersen" <martin.petersen@...cle.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Christoffer Dall <christoffer.dall@...aro.org>,
Dave Kleikamp <dave.kleikamp@...cle.com>, Jan Kara <jack@...e.cz>,
Luis de Bethencourt <luisbg@...nel.org>,
Marc Zyngier
<marc.zyngier@....com>, Rik van Riel <riel@...hat.com>,
Matthew Garrett <mjg59@...gle.com>, linux-fsdevel@...r.kernel.org,
linux-arch@...r.kernel.org, netdev@...r.kernel.org,
kernel-hardening@...ts.openwall.com, Vlastimil Babka <vbabka@...e.cz>,
Michal Kubecek <mkubecek@...e.cz>
Subject: Re: [PATCH 09/38] usercopy: Mark kmalloc caches as
usercopy caches
On 29.01.20 18:09, Christoph Hellwig wrote:
> On Wed, Jan 29, 2020 at 06:07:14PM +0100, Christian Borntraeger wrote:
>>> DMA can be done to NORMAL memory as well.
>>
>> Exactly.
>> I think iucv uses GFP_DMA because z/VM needs those buffers to reside below 2GB (which is ZONA_DMA for s390).
>
> The normal way to allocate memory with addressing limits would be to
> use dma_alloc_coherent and friends. Any chance to switch iucv over to
> that? Or is there no device associated with it?
There is not necessarily a device for that. It is a hypervisor interface (an
instruction that is interpreted by z/VM). We do have the netiucv driver that
creates a virtual nic, but there is also AF_IUCV which works without a device.
But back to the original question: If we mark kmalloc caches as usercopy caches,
we should do the same for DMA kmalloc caches. As outlined by Christoph, this has
nothing to do with device DMA.
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