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Re: [Xen-devel] [PATCH V3 8/8] iommu/arm: Add Renesas IPMMU-VMSA support

On 29.08.19 11:37, Yoshihiro Shimoda wrote:
Hi Oleksandr-san,

Hi Shimoda-san.

From: Oleksandr Tyshchenko, Sent: Wednesday, August 21, 2019 3:10 AM

From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>

The IPMMU-VMSA is VMSA-compatible I/O Memory Management Unit (IOMMU)
which provides address translation and access protection functionalities
to processing units and interconnect networks.

Please note, current driver is supposed to work only with newest
Gen3 SoCs revisions which IPMMU hardware supports stage 2 translation
This is still "Gen3", so that please replace it with "R-Car Gen3"...

Will do.

table format and is able to use CPU's P2M table as is if one is
3-level page table (up to 40 bit IPA).

The major differences compare to the Linux driver are:

1. Stage 1/Stage 2 translation. Linux driver supports Stage 1
translation only (with Stage 1 translation table format). It manages
page table by itself. But Xen driver supports Stage 2 translation
(with Stage 2 translation table format) to be able to share the P2M
with the CPU. Stage 1 translation is always bypassed in Xen driver.

So, Xen driver is supposed to be used with newest R-Car Gen3 SoC revisions
only (H3 ES3.0, M3-W+, etc.) which IPMMU H/W supports stage 2 translation
table format.

2. AArch64 support. Linux driver uses VMSAv8-32 mode, while Xen driver
enables Armv8 VMSAv8-64 mode to cover up to 40 bit input address.

3. Context bank (sets of page table) usage. In Xen, each context bank is
mapped to one Xen domain. So, all devices being pass throughed to the
same Xen domain share the same context bank.

4. IPMMU device tracking. In Xen, all IOMMU devices are managed
by single driver instance. So, driver uses global list to keep track
of registered IPMMU devices.

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
CC: Julien Grall <julien.grall@xxxxxxx>
CC: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>
About this hardware handling, this patch seems good to me. But, since
I'm not familiar about Xen passthrough framework, I think I cannot
add my Reviewed-by tag into this patch. What do you think?

I am not completely sure regarding that, but I have seen cases when the people give their R-b not for the entire patch, but for a part of it.

Especially, when patch touches many sub-systems/archs. Would you mind if I specify what your R-b covers? -> [for the IPMMU H/W bits]

Thank you for the review.

Best regards,
Yoshihiro Shimoda


Oleksandr Tyshchenko

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