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Re: [PATCH v5 13/13] xen/arm: mmu: enable SMMU subsystem only in MMU
- To: Julien Grall <julien@xxxxxxx>
- From: Henry Wang <Henry.Wang@xxxxxxx>
- Date: Tue, 22 Aug 2023 02:11:33 +0000
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- Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Penny Zheng <Penny.Zheng@xxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Paul Durrant <paul@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Wei Chen <Wei.Chen@xxxxxxx>
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- Thread-topic: [PATCH v5 13/13] xen/arm: mmu: enable SMMU subsystem only in MMU
Hi Julien,
> On Aug 22, 2023, at 05:34, Julien Grall <julien@xxxxxxx> wrote:
>
> Hi,
>
> On 14/08/2023 05:25, Henry Wang wrote:
>> From: Penny Zheng <Penny.Zheng@xxxxxxx>
>> SMMU subsystem is only supported in MMU system, so we make it dependent
>> on CONFIG_HAS_MMU.
>
> "only supported" as in it doesn't work with Xen or the HW is not supporting
> it?
I think currently there are no hardware combination of MPU + SMMU, but
theoretically I think this is a valid combination since SMMU supports the linear
mapping. So would below reword looks good to you:
“Currently the hardware use case of connecting SMMU to MPU system is rarely
seen, so we make CONFIG_ARM_SMMU and CONFIG_ARM_SMMU_V3
dependent on CONFIG_MMU."
>
> Also, I am not entirely convinced that anything in passthrough would properly
> work with MPU. At least none of the IOMMU drivers are. So I would consider to
> completely disable HAS_PASSTHROUGH.
I agree, do you think adding below addition diff to this patch makes sense to
you?
If so I guess would also need to mention this in commit message.
```
diff --git a/xen/arch/arm/Kconfig b/xen/arch/arm/Kconfig
index 8a7b79b4b5..fd29d14ed6 100644
--- a/xen/arch/arm/Kconfig
+++ b/xen/arch/arm/Kconfig
@@ -13,7 +13,7 @@ config ARM
def_bool y
select HAS_ALTERNATIVE
select HAS_DEVICE_TREE
- select HAS_PASSTHROUGH
+ select HAS_PASSTHROUGH if MMU
select HAS_PDX
select HAS_UBSAN
select IOMMU_FORCE_PT_SHARE
```
Kind regards,
Henry
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