Re: [Qemu-devel] [PATCH] target/arm: v8M MPU should use background region as default, not always

[Richard Henderson <richard.henderson@linaro.org>]

On 2/14/19 3:34 AM, Peter Maydell wrote:
> The "background region" for a v8M MPU is a default which will be used
> (if enabled, and if the access is privileged) if the access does
> not match any specific MPU region. We were incorrectly using it
> always (by putting the condition at the wrong nesting level). This
> meant that we would always return the default background permissions
> rather than the correct permissions for a specific region, and also
> that we would not return the right information in response to a
> TT instruction.
> 
> Move the check for the background region to the same place in the
> logic as the equivalent v8M MPUCheck() pseudocode puts it.
> This in turn means we must adjust the condition we use to detect
> matches in multiple regions to avoid false-positives.
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> I found this because the incorrect TT response eventually resulted
> in the Zephyr RTOS writing an invalid region number back to the
> NVIC and tripping the guest_errors logging.
> ---
>  target/arm/helper.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~