From: tfiga@google.com (Tomasz Figa)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 2/5] iommu/mediatek: Add mt8173 IOMMU driver
Date: Wed, 15 Apr 2015 16:41:17 +0900 [thread overview]
Message-ID: <CAAFQd5A2FgsbusEbxVVqSeC7hY=Ewe-YbJ7bbvk-SjpSC==xDw@mail.gmail.com> (raw)
In-Reply-To: <1429081567.16400.16.camel@mhfsdcap03>
On Wed, Apr 15, 2015 at 4:06 PM, Yong Wu <yong.wu@mediatek.com> wrote:
> On Wed, 2015-04-15 at 11:20 +0900, Tomasz Figa wrote:
>> On Tue, Apr 14, 2015 at 3:31 PM, Yong Wu <yong.wu@mediatek.com> wrote:
>> >> >>
>> >> >> > +
>> >> >> > + piommu->protect_va = devm_kmalloc(piommu->dev, MTK_PROTECT_PA_ALIGN*2,
>> >> >>
>> >> >> style: Operators like * should have space on both sides.
>> >> >>
>> >> >> > + GFP_KERNEL);
>> >> >>
>> >> >> Shouldn't dma_alloc_coherent() be used for this?
>> >> > We don't care the data in it. I think they are the same. Could you
>> >> > help tell me why dma_alloc_coherent may be better.
>> >>
>> >> Can you guarantee that at the time you allocate the memory using
>> >> devm_kmalloc() the memory is not dirty (i.e. some write back data are
>> >> stored in CPU cache) and is not going to be written back in some time,
>> >> overwriting data put there by IOMMU hardware?
>> >>
>> > As I noted in the function "mtk_iommu_hw_init":
>> >
>> > /* protect memory,HW will write here while translation fault */
>> > protectpa = __virt_to_phys(piommu->protect_va);
>> >
>> > We don?t care the content of this buffer, It is ok even though its
>> > data is dirty.
>> > It seem to be a the protect memory. While a translation fault
>> > happened, The iommu HW will overwrite here instead of writing to the
>> > fault physical address which may be 0 or some random address.
>> >
>>
>> Do you mean that it's just a dummy page for hardware behind the IOMMU
>> to access when the mapping is not available? How would that work with
>> potential on demand paging when the hardware needs to be blocked until
>> the mapping is created?
>>
>> Best regards,
>> Tomasz
> 1. YES
> 2. Sorry. Our iommu HW can not support this right now. The HW can not
> be blocked until the mapping is created.
OK, that explains it. Well, then I guess this is necessary and
contents of that memory don't matter that much. (Although, this might
be a minor security issue, because the faulting hardware would get
access to some data previously stored by kernel code. Not sure how
much of a threat would that be, though.)
> If the page is not ready, we can not get the physical address, then
> How to fill the pagetable for that memory. I think the dma&iommu may
> guaranty it?
If your hardware can't block until the mapping is created then what
you do currently seems to be the only option. (+/- the missing cache
maintenance at initialization)
Best regards,
Tomasz
next prev parent reply other threads:[~2015-04-15 7:41 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-06 10:48 [RFC PATCH 0/5] MT8173 IOMMU support yong.wu at mediatek.com
2015-03-06 10:48 ` [PATCH 1/5] soc: mediatek: Add SMI driver yong.wu at mediatek.com
2015-03-06 11:30 ` Paul Bolle
2015-03-09 11:57 ` Yong Wu
2015-03-09 17:59 ` Paul Bolle
2015-03-09 21:54 ` Arnd Bergmann
2015-03-10 6:17 ` Yingjoe Chen
2015-03-09 3:26 ` Yingjoe Chen
2015-03-09 21:56 ` Arnd Bergmann
2015-03-10 6:27 ` Yingjoe Chen
2015-03-10 9:05 ` Arnd Bergmann
2015-03-10 9:24 ` Lucas Stach
2015-03-09 11:03 ` Sascha Hauer
2015-03-06 10:48 ` [PATCH 2/5] iommu/mediatek: Add mt8173 IOMMU driver yong.wu at mediatek.com
2015-03-06 10:58 ` Will Deacon
2015-03-09 12:11 ` Yong Wu
2015-03-17 15:14 ` Will Deacon
2015-03-06 17:15 ` Mitchel Humpherys
2015-03-09 12:16 ` Yong Wu
2015-03-09 16:57 ` Mitchel Humpherys
2015-03-08 4:12 ` Tomasz Figa
2015-03-12 14:16 ` Yong Wu
2015-03-09 8:24 ` Daniel Kurtz
2015-03-09 11:11 ` Tomasz Figa
2015-03-09 14:46 ` Yingjoe Chen
2015-03-09 17:00 ` Tomasz Figa
2015-03-10 3:41 ` Yingjoe Chen
2015-03-10 4:06 ` Tomasz Figa
2015-03-11 10:53 ` Tomasz Figa
2015-03-18 11:22 ` Yong Wu
2015-03-20 19:14 ` Robin Murphy
2015-04-14 6:50 ` Yong Wu
2015-03-27 9:41 ` Tomasz Figa
2015-04-14 6:31 ` Yong Wu
2015-04-15 2:20 ` Tomasz Figa
2015-04-15 7:06 ` Yong Wu
2015-04-15 7:41 ` Tomasz Figa [this message]
2015-04-29 6:23 ` Yong Wu
2015-03-06 10:48 ` [PATCH 3/5] dt-bindings: mediatek: Add smi dts binding yong.wu at mediatek.com
2015-03-06 11:13 ` Mark Rutland
2015-03-09 12:55 ` Yong Wu
2015-04-14 9:07 ` Yong Wu
2015-04-14 10:06 ` Mark Rutland
2015-04-14 13:49 ` Yong Wu
2015-04-14 13:55 ` Yong Wu
2015-04-14 13:56 ` Mark Rutland
2015-03-06 14:48 ` Sergei Shtylyov
2015-03-09 12:32 ` Yong Wu
2015-03-06 10:48 ` [PATCH 4/5] dt-bindings: iommu: Add binding for mediatek IOMMU yong.wu at mediatek.com
2015-03-06 11:21 ` Mark Rutland
2015-03-09 11:30 ` Yong Wu
2015-03-06 10:48 ` [PATCH 5/5] dts: mt8173: Add iommu/smi nodes for mt8173 yong.wu at mediatek.com
2015-03-07 15:20 ` Daniel Kurtz
2015-03-09 12:18 ` Yong Wu
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