From: Christoph Hellwig <hch@lst.de>
To: Alexey Kardashevskiy <aik@ozlabs.ru>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Robin Murphy <robin.murphy@arm.com>,
linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org,
Michael Ellerman <mpe@ellerman.id.au>,
"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
linuxppc-dev@lists.ozlabs.org, Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH 1/2] dma-mapping: add a dma_ops_bypass flag to struct device
Date: Mon, 6 Apr 2020 13:50:16 +0200 [thread overview]
Message-ID: <20200406115016.GA10941@lst.de> (raw)
In-Reply-To: <213b0c7d-f908-b4f4-466d-6240c3622cd6@ozlabs.ru>
On Fri, Apr 03, 2020 at 07:38:11PM +1100, Alexey Kardashevskiy wrote:
>
>
> On 26/03/2020 12:26, Alexey Kardashevskiy wrote:
> >
> >
> > On 25/03/2020 19:37, Christoph Hellwig wrote:
> >> On Wed, Mar 25, 2020 at 03:51:36PM +1100, Alexey Kardashevskiy wrote:
> >>>>> This is for persistent memory which you can DMA to/from but yet it does
> >>>>> not appear in the system as a normal memory and therefore requires
> >>>>> special handling anyway (O_DIRECT or DAX, I do not know the exact
> >>>>> mechanics). All other devices in the system should just run as usual,
> >>>>> i.e. use 1:1 mapping if possible.
> >>>>
> >>>> On other systems (x86 and arm) pmem as long as it is page backed does
> >>>> not require any special handling. This must be some weird way powerpc
> >>>> fucked up again, and I suspect you'll have to suffer from it.
> >>>
> >>>
> >>> It does not matter if it is backed by pages or not, the problem may also
> >>> appear if we wanted for example p2p PCI via IOMMU (between PHBs) and
> >>> MMIO might be mapped way too high in the system address space and make
> >>> 1:1 impossible.
> >>
> >> How can it be mapped too high for a direct mapping with a 64-bit DMA
> >> mask?
> >
> > The window size is limited and often it is not even sparse. It requires
> > an 8 byte entry per an IOMMU page (which is most commonly is 64k max) so
> > 1TB limit (a guest RAM size) is a quite real thing. MMIO is mapped to
> > guest physical address space outside of this 1TB (on PPC).
> >
> >
>
> I am trying now this approach on top of yours "dma-bypass.3" (it is
> "wip", needs an upper boundary check):
>
> https://github.com/aik/linux/commit/49d73c7771e3f6054804f6cfa80b4e320111662d
>
> Do you see any serious problem with this approach? Thanks!
Do you have a link to the whole branch? The github UI is unfortunately
unusable for that (or I'm missing something).
_______________________________________________
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu
WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@lst.de>
To: Alexey Kardashevskiy <aik@ozlabs.ru>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Joerg Roedel <joro@8bytes.org>,
Robin Murphy <robin.murphy@arm.com>,
linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org,
"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
linuxppc-dev@lists.ozlabs.org, Christoph Hellwig <hch@lst.de>,
Lu Baolu <baolu.lu@linux.intel.com>
Subject: Re: [PATCH 1/2] dma-mapping: add a dma_ops_bypass flag to struct device
Date: Mon, 6 Apr 2020 13:50:16 +0200 [thread overview]
Message-ID: <20200406115016.GA10941@lst.de> (raw)
In-Reply-To: <213b0c7d-f908-b4f4-466d-6240c3622cd6@ozlabs.ru>
On Fri, Apr 03, 2020 at 07:38:11PM +1100, Alexey Kardashevskiy wrote:
>
>
> On 26/03/2020 12:26, Alexey Kardashevskiy wrote:
> >
> >
> > On 25/03/2020 19:37, Christoph Hellwig wrote:
> >> On Wed, Mar 25, 2020 at 03:51:36PM +1100, Alexey Kardashevskiy wrote:
> >>>>> This is for persistent memory which you can DMA to/from but yet it does
> >>>>> not appear in the system as a normal memory and therefore requires
> >>>>> special handling anyway (O_DIRECT or DAX, I do not know the exact
> >>>>> mechanics). All other devices in the system should just run as usual,
> >>>>> i.e. use 1:1 mapping if possible.
> >>>>
> >>>> On other systems (x86 and arm) pmem as long as it is page backed does
> >>>> not require any special handling. This must be some weird way powerpc
> >>>> fucked up again, and I suspect you'll have to suffer from it.
> >>>
> >>>
> >>> It does not matter if it is backed by pages or not, the problem may also
> >>> appear if we wanted for example p2p PCI via IOMMU (between PHBs) and
> >>> MMIO might be mapped way too high in the system address space and make
> >>> 1:1 impossible.
> >>
> >> How can it be mapped too high for a direct mapping with a 64-bit DMA
> >> mask?
> >
> > The window size is limited and often it is not even sparse. It requires
> > an 8 byte entry per an IOMMU page (which is most commonly is 64k max) so
> > 1TB limit (a guest RAM size) is a quite real thing. MMIO is mapped to
> > guest physical address space outside of this 1TB (on PPC).
> >
> >
>
> I am trying now this approach on top of yours "dma-bypass.3" (it is
> "wip", needs an upper boundary check):
>
> https://github.com/aik/linux/commit/49d73c7771e3f6054804f6cfa80b4e320111662d
>
> Do you see any serious problem with this approach? Thanks!
Do you have a link to the whole branch? The github UI is unfortunately
unusable for that (or I'm missing something).
WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@lst.de>
To: Alexey Kardashevskiy <aik@ozlabs.ru>
Cc: Christoph Hellwig <hch@lst.de>,
"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
iommu@lists.linux-foundation.org, linuxppc-dev@lists.ozlabs.org,
Lu Baolu <baolu.lu@linux.intel.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Joerg Roedel <joro@8bytes.org>,
Robin Murphy <robin.murphy@arm.com>,
linux-kernel@vger.kernel.org,
Michael Ellerman <mpe@ellerman.id.au>
Subject: Re: [PATCH 1/2] dma-mapping: add a dma_ops_bypass flag to struct device
Date: Mon, 6 Apr 2020 13:50:16 +0200 [thread overview]
Message-ID: <20200406115016.GA10941@lst.de> (raw)
In-Reply-To: <213b0c7d-f908-b4f4-466d-6240c3622cd6@ozlabs.ru>
On Fri, Apr 03, 2020 at 07:38:11PM +1100, Alexey Kardashevskiy wrote:
>
>
> On 26/03/2020 12:26, Alexey Kardashevskiy wrote:
> >
> >
> > On 25/03/2020 19:37, Christoph Hellwig wrote:
> >> On Wed, Mar 25, 2020 at 03:51:36PM +1100, Alexey Kardashevskiy wrote:
> >>>>> This is for persistent memory which you can DMA to/from but yet it does
> >>>>> not appear in the system as a normal memory and therefore requires
> >>>>> special handling anyway (O_DIRECT or DAX, I do not know the exact
> >>>>> mechanics). All other devices in the system should just run as usual,
> >>>>> i.e. use 1:1 mapping if possible.
> >>>>
> >>>> On other systems (x86 and arm) pmem as long as it is page backed does
> >>>> not require any special handling. This must be some weird way powerpc
> >>>> fucked up again, and I suspect you'll have to suffer from it.
> >>>
> >>>
> >>> It does not matter if it is backed by pages or not, the problem may also
> >>> appear if we wanted for example p2p PCI via IOMMU (between PHBs) and
> >>> MMIO might be mapped way too high in the system address space and make
> >>> 1:1 impossible.
> >>
> >> How can it be mapped too high for a direct mapping with a 64-bit DMA
> >> mask?
> >
> > The window size is limited and often it is not even sparse. It requires
> > an 8 byte entry per an IOMMU page (which is most commonly is 64k max) so
> > 1TB limit (a guest RAM size) is a quite real thing. MMIO is mapped to
> > guest physical address space outside of this 1TB (on PPC).
> >
> >
>
> I am trying now this approach on top of yours "dma-bypass.3" (it is
> "wip", needs an upper boundary check):
>
> https://github.com/aik/linux/commit/49d73c7771e3f6054804f6cfa80b4e320111662d
>
> Do you see any serious problem with this approach? Thanks!
Do you have a link to the whole branch? The github UI is unfortunately
unusable for that (or I'm missing something).
next prev parent reply other threads:[~2020-04-06 11:50 UTC|newest]
Thread overview: 94+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-20 14:16 generic DMA bypass flag v2 Christoph Hellwig
2020-03-20 14:16 ` Christoph Hellwig
2020-03-20 14:16 ` Christoph Hellwig
2020-03-20 14:16 ` [PATCH 1/2] dma-mapping: add a dma_ops_bypass flag to struct device Christoph Hellwig
2020-03-20 14:16 ` Christoph Hellwig
2020-03-20 14:16 ` Christoph Hellwig
2020-03-20 15:02 ` Greg Kroah-Hartman
2020-03-20 15:02 ` Greg Kroah-Hartman
2020-03-20 15:02 ` Greg Kroah-Hartman
2020-03-23 1:28 ` Alexey Kardashevskiy
2020-03-23 1:28 ` Alexey Kardashevskiy
2020-03-23 1:28 ` Alexey Kardashevskiy
2020-03-23 8:37 ` Christoph Hellwig
2020-03-23 8:37 ` Christoph Hellwig
2020-03-23 8:37 ` Christoph Hellwig
2020-03-23 8:50 ` Christoph Hellwig
2020-03-23 8:50 ` Christoph Hellwig
2020-03-23 8:50 ` Christoph Hellwig
2020-03-23 15:37 ` Aneesh Kumar K.V
2020-03-23 15:37 ` Aneesh Kumar K.V
2020-03-23 15:37 ` Aneesh Kumar K.V
2020-03-23 17:22 ` Christoph Hellwig
2020-03-23 17:22 ` Christoph Hellwig
2020-03-23 17:22 ` Christoph Hellwig
2020-03-24 3:05 ` Alexey Kardashevskiy
2020-03-24 3:05 ` Alexey Kardashevskiy
2020-03-24 3:05 ` Alexey Kardashevskiy
2020-03-24 6:30 ` Aneesh Kumar K.V
2020-03-24 6:30 ` Aneesh Kumar K.V
2020-03-24 6:30 ` Aneesh Kumar K.V
2020-03-24 7:55 ` Christoph Hellwig
2020-03-24 7:55 ` Christoph Hellwig
2020-03-24 7:55 ` Christoph Hellwig
2020-03-24 7:54 ` Christoph Hellwig
2020-03-24 7:54 ` Christoph Hellwig
2020-03-24 7:54 ` Christoph Hellwig
2020-03-25 4:51 ` Alexey Kardashevskiy
2020-03-25 4:51 ` Alexey Kardashevskiy
2020-03-25 4:51 ` Alexey Kardashevskiy
2020-03-25 8:37 ` Christoph Hellwig
2020-03-25 8:37 ` Christoph Hellwig
2020-03-25 8:37 ` Christoph Hellwig
2020-03-26 1:26 ` Alexey Kardashevskiy
2020-03-26 1:26 ` Alexey Kardashevskiy
2020-03-26 1:26 ` Alexey Kardashevskiy
2020-04-03 8:38 ` Alexey Kardashevskiy
2020-04-03 8:38 ` Alexey Kardashevskiy
2020-04-03 8:38 ` Alexey Kardashevskiy
2020-04-06 11:50 ` Christoph Hellwig [this message]
2020-04-06 11:50 ` Christoph Hellwig
2020-04-06 11:50 ` Christoph Hellwig
2020-04-06 13:25 ` Alexey Kardashevskiy
2020-04-06 13:25 ` Alexey Kardashevskiy
2020-04-06 13:25 ` Alexey Kardashevskiy
2020-04-06 17:17 ` Christoph Hellwig
2020-04-06 17:17 ` Christoph Hellwig
2020-04-06 17:17 ` Christoph Hellwig
2020-04-07 10:12 ` Alexey Kardashevskiy
2020-04-07 10:12 ` Alexey Kardashevskiy
2020-04-07 10:12 ` Alexey Kardashevskiy
2020-04-14 6:21 ` Alexey Kardashevskiy
2020-04-14 6:21 ` Alexey Kardashevskiy
2020-04-14 6:21 ` Alexey Kardashevskiy
2020-04-14 6:30 ` Christoph Hellwig
2020-04-14 6:30 ` Christoph Hellwig
2020-04-14 6:30 ` Christoph Hellwig
2020-03-23 8:58 ` Alexey Kardashevskiy
2020-03-23 8:58 ` Alexey Kardashevskiy
2020-03-23 8:58 ` Alexey Kardashevskiy
2020-03-23 17:20 ` Christoph Hellwig
2020-03-23 17:20 ` Christoph Hellwig
2020-03-23 17:20 ` Christoph Hellwig
2020-03-24 3:37 ` Alexey Kardashevskiy
2020-03-24 3:37 ` Alexey Kardashevskiy
2020-03-24 3:37 ` Alexey Kardashevskiy
2020-03-24 4:55 ` Alexey Kardashevskiy
2020-03-24 4:55 ` Alexey Kardashevskiy
2020-03-24 4:55 ` Alexey Kardashevskiy
2020-03-24 7:52 ` Christoph Hellwig
2020-03-24 7:52 ` Christoph Hellwig
2020-03-24 7:52 ` Christoph Hellwig
2020-03-23 12:14 ` Robin Murphy
2020-03-23 12:14 ` Robin Murphy
2020-03-23 12:14 ` Robin Murphy
2020-03-23 12:55 ` Christoph Hellwig
2020-03-23 12:55 ` Christoph Hellwig
2020-03-23 12:55 ` Christoph Hellwig
2020-03-20 14:16 ` [PATCH 2/2] powerpc: use the generic dma_ops_bypass mode Christoph Hellwig
2020-03-20 14:16 ` Christoph Hellwig
2020-03-20 14:16 ` Christoph Hellwig
-- strict thread matches above, loose matches on Subject: below --
2020-03-24 9:39 [PATCH 1/2] dma-mapping: add a dma_ops_bypass flag to, struct device Christian Zigotzky
2019-11-13 13:37 generic DMA bypass flag Christoph Hellwig
2019-11-13 13:37 ` [PATCH 1/2] dma-mapping: add a dma_ops_bypass flag to struct device Christoph Hellwig
2019-11-13 13:37 ` Christoph Hellwig
2019-11-13 13:37 ` Christoph Hellwig
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