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Re: [Xen-devel] [PATCH v2 00/13] "Non-shared" IOMMU support on ARM

On 01/08/17 04:06, Tian, Kevin wrote:
From: Oleksandr Tyshchenko [mailto:olekstysh@xxxxxxxxx]
Sent: Monday, July 31, 2017 7:58 PM

Hi, Kevin

On Mon, Jul 31, 2017 at 8:57 AM, Tian, Kevin <kevin.tian@xxxxxxxxx> wrote:
From: Oleksandr Tyshchenko
Sent: Wednesday, July 26, 2017 1:27 AM

From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>

Hi, all.

The purpose of this patch series is to create a base for porting
any "Non-shared" IOMMUs to Xen on ARM. Saying "Non-shared" IOMMU
the IOMMU that can't share the page table with the CPU.

Is "non-shared" IOMMU a standard terminology in ARM side? I quickly
searched to find it mostly used in this thread...
I don't think that it is a standard terminology.

On the other hand, all IOMMUs support a basic DMA remapping
mechanism with page table not shared with CPU. Then some IOMMUs
may optional support Shared Virtual Memory (SVM) through page
sharing with CPU. Then I'm not sure why need to highlight the
"non-shared" manner in this thread, instead of just saying
IPMMU-VMSA support...
I wouldn't use "IPMMU-VMSA support" in this thread since it may be any
other IOMMUs which can't share page table
with CPU because of format incompatibilities.

As I commented you can assume all IOMMUs cannot share page
table with CPU as the starting point. It's not good to name an IOMMU
driver based on such fact.

As said in a previous reply. This is a wrong assumption, you can share page-tables with the IOMMU if the format is the same. You may still need to do TLB flush manually on the IOMMU, but you still save memory.

x86 is already supporting that and also call "sharing" and is done by default (see iommu_hap_pt_share). If the naming is wrong, then feel free to send a patch.

But I don't think you should complain about Oleksandr use this name.


Julien Grall

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