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Re: [Xen-devel] [PATCH v5 09/12] arm/mem_access: Add software guest-page-table walk

Hi Julien,

>>> In this case, you need a bit more rationale to explain why setting to
>>> GV2M_READ by default is fine... If it is just a random value, then
>>> say it.
>> I will add a comment in the change log stating that we set perms to
>> GV2M_READ (that equals to 0) by default to avoid having potentially
>> random values returned on errors.
> Beware that you are re-using GV2M_READ for different purpose. In the
> current code it is used to check whether a guest VA is readable.
> Here, you are using both GV2M_* to return the permissions of a
> mapping. What matters is whether it is fine to consider a page will
> always have the read permission.
> At the moment, you consider you will always translate the VA -> IPA
> with EL1 permission (see D4-29 in ARM DDI 0487B.a). So the resulting
> permission in stage-1 will always contain read.
> I am ok if you make this assumption, but this needs to be explained in
> a comment in the code. So we are not surprised in the future why you
> always set read permission.

Alright. I will state in a comment in code and change-log that since the
current implementation considers a valid mapping as readable at least by
EL1 because the current implementation does not consider further
attributes responsible for distinguishing between EL0 and EL1. Thank you.

>> Shall I remove your ack for this patch in the next version?
> Yes please.
> Cheers,


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