Re: [Qemu-arm] [Qemu-devel] [PATCH for-3.0] target/arm: Correctly handle overlapping small MPU regions

[Richard Henderson]

On 07/16/2018 06:33 AM, Peter Maydell wrote:
> @@ -9963,6 +9994,21 @@ static bool pmsav8_mpu_lookup(CPUARMState *env, 
> uint32_t address,
>              }
>  
>              if (address < base || address > limit) {> +                /*> + 
>                 * Address not in this region. We must
check whether the> +                 * region covers addresses in the same page
as our address.> +                 * In that case we must not report a size
that covers the> +                 * whole page for a subsequent hit against a
different MPU> +                 * region or the background region, because it
would result in> +                 * incorrect TLB hits for subsequent accesses
to addresses that> +                 * are in this MPU region.> +
  */> +                if (limit >= base &&> +
ranges_overlap(base, limit - base + 1,> +
addr_page_base,> +                                   TARGET_PAGE_SIZE)) {> +
                *is_subpage = true;> +                }
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).

Because of the non-fault for region overlap in v7m, I can see that the test is
required in get_phys_addr_pmsav7, but AFAICS only there.


r~