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Re: [Xen-devel] [PATCH v3 3/3] xen/iommu: arm: Use p2m_ipa_bits as stage2 input size

Hi Edgar,

On 01/05/15 02:39, Edgar E. Iglesias wrote:
> On Thu, Apr 30, 2015 at 04:07:27PM +0100, Julien Grall wrote:
>> As this is a restriction of the driver we should print a error message
>> and return an appropriate error value.
>> The generic IOMMU driver can then decide if it's safe to continue
>> without the SMMU setup or panic.
>> FWIW, currently we use the later. I will send a patch to panic avoiding

Hmmm... I meant former not later here.

>> the user to think the SMMU is correctly setup.
> This is what it looks like in my new version when starting XEN and forcing
> a bad SMMU IPA size:
> (XEN) P2M: 40-bit IPA with 40-bit PA
> (XEN) P2M: 3 levels with order-1 root, VTCR 0x80023558
> (XEN) smmu: /amba/smmu0@0xFD800000: probing hardware configuration...
> (XEN) smmu: /amba/smmu0@0xFD800000: SMMUv2 with:
> (XEN) smmu: /amba/smmu0@0xFD800000:     stage 2 translation
> (XEN) smmu: /amba/smmu0@0xFD800000:     stream matching with 48 register 
> groups, mask 0x7fff
> (XEN) smmu: /amba/smmu0@0xFD800000:     16 context banks (0 stage-2 only)
> (XEN) smmu: /amba/smmu0@0xFD800000: P2M IPA size not supported (P2M=40 
> SMMU=36)!
> (XEN) I/O virtualisation disabled
> (XEN) *** LOADING DOMAIN 0 ***
> Dom0 boots fine but without IOMMU protections...

I was expected this behavior. IOMMU is only important for device
passthrough. In this case, the user won't be able to assign the device
protected by this SMMU to any guest.

We currently have the same behavior as x86. Xen will continue to boot
DOM0 unless "iommu=force/required" is passed on the command line.

I think we should keep the same behavior.


Julien Grall

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