Re: [PATCH 3/5] arm/mpu: Implement transient mapping

["Orzel, Michal" <michal.orzel@xxxxxxx>]

On 30/07/2025 10:45, Hari Limaye wrote:
> From: Luca Fancellu <luca.fancellu@xxxxxxx>
> 
> Add a scheme to distinguish transient MPU regions, to identify MPU
> regions which will be mapped for a short period of time.
The commit msg lacks description why this is needed.

> 
> Signed-off-by: Luca Fancellu <luca.fancellu@xxxxxxx>
> Signed-off-by: Hari Limaye <hari.limaye@xxxxxxx>
> ---
>  xen/arch/arm/include/asm/arm32/mpu.h     |  2 ++
>  xen/arch/arm/include/asm/arm64/mpu.h     |  2 ++
>  xen/arch/arm/include/asm/mpu/mm.h        | 14 +++++++++++++-
>  xen/arch/arm/include/asm/mpu/regions.inc | 19 +++++++++++++++++--
>  xen/arch/arm/mpu/mm.c                    | 23 ++++++++++++++---------
>  5 files changed, 48 insertions(+), 12 deletions(-)
> 
> diff --git a/xen/arch/arm/include/asm/arm32/mpu.h 
> b/xen/arch/arm/include/asm/arm32/mpu.h
> index 0a6930b3a0..9906d98809 100644
> --- a/xen/arch/arm/include/asm/arm32/mpu.h
> +++ b/xen/arch/arm/include/asm/arm32/mpu.h
> @@ -39,6 +39,8 @@ typedef union {
>  typedef struct {
>      prbar_t prbar;
>      prlar_t prlar;
> +    bool transient;
> +    uint8_t pad[7]; /* Pad structure to 16 Bytes */
>  } pr_t;
>  
>  #endif /* __ASSEMBLY__ */
> diff --git a/xen/arch/arm/include/asm/arm64/mpu.h 
> b/xen/arch/arm/include/asm/arm64/mpu.h
> index f0ce344e78..1d1843eda0 100644
> --- a/xen/arch/arm/include/asm/arm64/mpu.h
> +++ b/xen/arch/arm/include/asm/arm64/mpu.h
> @@ -38,6 +38,8 @@ typedef union {
>  typedef struct {
>      prbar_t prbar;
>      prlar_t prlar;
> +    bool transient;
> +    uint8_t pad[15]; /* Pad structure to 32 Bytes */
>  } pr_t;
>  
>  #endif /* __ASSEMBLY__ */
> diff --git a/xen/arch/arm/include/asm/mpu/mm.h 
> b/xen/arch/arm/include/asm/mpu/mm.h
> index c32fac8905..56ca411af4 100644
> --- a/xen/arch/arm/include/asm/mpu/mm.h
> +++ b/xen/arch/arm/include/asm/mpu/mm.h
> @@ -60,6 +60,16 @@ static inline void context_sync_mpu(void)
>      isb();
>  }
>  
> +static inline bool region_is_transient(pr_t *pr)
As this is just a read helper, pr could be const?

~Michal