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Re: [Qemu-devel] [PATCH for-3.0] target/arm: Correctly handle overlappin

From: Richard Henderson
Subject: Re: [Qemu-devel] [PATCH for-3.0] target/arm: Correctly handle overlapping small MPU regions
Date: Tue, 17 Jul 2018 21:02:37 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0

On 07/17/2018 12:40 PM, Peter Maydell wrote:
> On 17 July 2018 at 18:29, Richard Henderson
> <address@hidden> wrote:
>> I don't understand why this is necessary in the v8m case.
>>                AP                 APL
>>     <----B1----|----L1-B2-A-------|---L2--->
>> Your comment posits two regions [B1,L1] and [B2,L2], that A is not within
>> [B1,L1] but is within [B2,L2] (otherwise we would not report a hit at all).
>> Further, that [B1,L1] intersects [AP,APL] but does not intersect [B2,L2]
>> (otherwise we would report a fault for overlapping regions).
>> Surely this combination of ranges implies that [B2,L2] must itself set
>> IS_SUBPAGE (otherwise the first region would not overlap the page of A, or
>> would not overlap the second region).
> (a) the overlap fault is only for addresses which are actually in the
> overlap (ie "you asked about address X and it hits in R1 and R2"); it
> doesn't imply that other addresses which are only in R1 fault just
> because some part of R1 overlaps with R2.

Ah, that wasn't clear from the manual.

> So for instance:
>        AP                        APL
>    [B1                                L1]
>                  [B2       L2]
>              A1^     A2^

Thanks for the example,

Reviewed-by: Richard Henderson <address@hidden>


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