Re: [PATCH v2 3/5] arm/mpu: Implement transient mapping

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

On 27/08/2025 18:35, 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. This is needed
> for the functions which transiently map and unmap memory ranges on
> demand which will be introduced in a future commit.
> 
> Signed-off-by: Luca Fancellu <luca.fancellu@xxxxxxx>
> Signed-off-by: Hari Limaye <hari.limaye@xxxxxxx>
> ---
> Changes from v1:
> - Improve commit message
> - Mark parameter in read helper as const
> ---
>  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;
Do we expect to have any other flags? If so, it could make sense to use a
bitfield right away.

> +    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 e1ded6521d..566d338986 100644
> --- a/xen/arch/arm/include/asm/mpu/mm.h
> +++ b/xen/arch/arm/include/asm/mpu/mm.h
> @@ -55,6 +55,16 @@ static inline void context_sync_mpu(void)
>      isb();
>  }
>  
> +static inline bool region_is_transient(const pr_t *pr)
> +{
> +    return pr->transient;
> +}
> +
> +static inline void region_set_transient(pr_t *pr, bool transient)
> +{
> +    pr->transient = transient;
> +}
> +
>  /*
>   * The following API requires context_sync_mpu() after being used to modify 
> MPU
>   * regions:
> @@ -75,9 +85,11 @@ void write_protection_region(const pr_t *pr_write, uint8_t 
> sel);
>   * @param base      Base address of the range to map (inclusive).
>   * @param limit     Limit address of the range to map (exclusive).
>   * @param flags     Flags for the memory range to map.
> + * @param transient True for a transient mapping, otherwise False.
>   * @return          0 on success, negative on error.
>   */
> -int xen_mpumap_update(paddr_t base, paddr_t limit, unsigned int flags);
> +int xen_mpumap_update(paddr_t base, paddr_t limit, unsigned int flags,
> +                      bool transient);
>  
>  /*
>   * Creates a pr_t structure describing a protection region.
> diff --git a/xen/arch/arm/include/asm/mpu/regions.inc 
> b/xen/arch/arm/include/asm/mpu/regions.inc
> index 23fead3b21..f9892fe3d8 100644
> --- a/xen/arch/arm/include/asm/mpu/regions.inc
> +++ b/xen/arch/arm/include/asm/mpu/regions.inc
> @@ -14,19 +14,31 @@
>  #define PRLAR_ELx_EN            0x1
>  
>  #ifdef CONFIG_ARM_64
> -#define XEN_MPUMAP_ENTRY_SHIFT  0x4     /* 16 byte structure */
> +#define XEN_MPUMAP_ENTRY_SHIFT        0x5   /* 32 byte structure */
> +#define XEN_MPUMAP_ENTRY_ZERO_OFFSET  0x10  /* {PRBAR, PRLAR} is 16 bytes  */
To avoid having to update this over and over again, maybe define a macro using
OFFSET?

Other than that:
Reviewed-by: Michal Orzel <michal.orzel@xxxxxxx>

~Michal