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Re: [PATCH v4 3/3] arm/mpu: Enable read/write to protection regions for arm32

Hi Ayan,

On 17/06/2025 12:12, Ayan Kumar Halder wrote:

Define prepare_selector(), read_protection_region() and
write_protection_region() for arm32. Also, define
GENERATE_{READ/WRITE}_PR_REG_OTHERS to access MPU regions from 32 to 254.

Enable pr_{get/set}_{base/limit}(), region_is_valid() for arm32.
Enable pr_of_addr() for arm32.

The maximum number of regions supported is 255 (which corresponds to the
maximum value in HMPUIR).

Signed-off-by: Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>


Acked-by: Julien Grall <jgrall@xxxxxxxxxx>

Cheers,


---
Changes from :-

v1 - 1. Enable write_protection_region() for aarch32.

v2 - 1. Enable access to protection regions from 0 - 255.

v3 - 1. The maximum number of regions is 255. Thus, regions numbered 0 - 254
are supported.

2. prepare_selector() is modified to ensure HPRSELR is written when accessing
any region beyond 31 and the current value differs from the region number to
be accessed.

  xen/arch/arm/include/asm/mpu.h  |   2 -
  xen/arch/arm/mpu/Makefile       |   1 +
  xen/arch/arm/mpu/arm32/Makefile |   1 +
  xen/arch/arm/mpu/arm32/mm.c     | 164 ++++++++++++++++++++++++++++++++
  xen/arch/arm/mpu/mm.c           |   2 -
  5 files changed, 166 insertions(+), 4 deletions(-)
  create mode 100644 xen/arch/arm/mpu/arm32/Makefile
  create mode 100644 xen/arch/arm/mpu/arm32/mm.c

diff --git a/xen/arch/arm/include/asm/mpu.h b/xen/arch/arm/include/asm/mpu.h
index 8f06ddac0f..63560c613b 100644
--- a/xen/arch/arm/include/asm/mpu.h
+++ b/xen/arch/arm/include/asm/mpu.h
@@ -25,7 +25,6 @@
#ifndef __ASSEMBLY__ -#ifdef CONFIG_ARM_64 
  /*
   * Set base address of MPU protection region.
   *
@@ -85,7 +84,6 @@ static inline bool region_is_valid(const pr_t *pr)
  {
      return pr->prlar.reg.en;
  }
-#endif /* CONFIG_ARM_64 */
#endif /* __ASSEMBLY__ */ diff --git a/xen/arch/arm/mpu/Makefile b/xen/arch/arm/mpu/Makefile 
index 5ad15e93be..58c9b5b4e8 100644
--- a/xen/arch/arm/mpu/Makefile
+++ b/xen/arch/arm/mpu/Makefile
@@ -1,4 +1,5 @@
  obj-$(CONFIG_ARM_32) += domain-page.o
+obj-$(CONFIG_ARM_32) += arm32/
  obj-$(CONFIG_ARM_64) += arm64/
  obj-y += mm.o
  obj-y += p2m.o
diff --git a/xen/arch/arm/mpu/arm32/Makefile b/xen/arch/arm/mpu/arm32/Makefile
new file mode 100644
index 0000000000..b18cec4836
--- /dev/null
+++ b/xen/arch/arm/mpu/arm32/Makefile
@@ -0,0 +1 @@
+obj-y += mm.o
diff --git a/xen/arch/arm/mpu/arm32/mm.c b/xen/arch/arm/mpu/arm32/mm.c
new file mode 100644
index 0000000000..c0317a4ada
--- /dev/null
+++ b/xen/arch/arm/mpu/arm32/mm.c
@@ -0,0 +1,164 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <xen/bug.h>
+#include <xen/types.h>
+#include <asm/mpu.h>
+#include <asm/sysregs.h>
+#include <asm/system.h>
+
+#define GENERATE_WRITE_PR_REG_CASE(num, pr)               \
+    case num:                                             \
+    {                                                     \
+        WRITE_SYSREG(pr->prbar.bits, HPRBAR##num);        \
+        WRITE_SYSREG(pr->prlar.bits, HPRLAR##num);        \
+        break;                                            \
+    }
+
+#define GENERATE_WRITE_PR_REG_OTHERS(num, pr)             \
+    case num:                                             \
+    {                                                     \
+        WRITE_SYSREG(pr->prbar.bits, HPRBAR);             \
+        WRITE_SYSREG(pr->prlar.bits, HPRLAR);             \
+        break;                                            \
+    }
+
+#define GENERATE_READ_PR_REG_CASE(num, pr)                \
+    case num:                                             \
+    {                                                     \
+        pr->prbar.bits = READ_SYSREG(HPRBAR##num);        \
+        pr->prlar.bits = READ_SYSREG(HPRLAR##num);        \
+        break;                                            \
+    }
+
+#define GENERATE_READ_PR_REG_OTHERS(num, pr)              \
+    case num:                                             \
+    {                                                     \
+        pr->prbar.bits = READ_SYSREG(HPRBAR);             \
+        pr->prlar.bits = READ_SYSREG(HPRLAR);             \
+        break;                                            \
+    }
+
+/*
+ * Armv8-R supports direct access and indirect access to the MPU regions 
through
+ * registers:
+ *  - indirect access involves changing the MPU region selector, issuing an isb
+ *    barrier and accessing the selected region through specific registers
+ *  - direct access involves accessing specific registers that point to
+ *    specific MPU regions, without changing the selector, avoiding the use of
+ *    a barrier.
+ * For Arm32 the HPR{B,L}AR<n> (for n=0..31) are used for direct access to the
+ * first 32 MPU regions.
+ * For MPU region numbered 32..254, one need to set the region number in 
HPRSELR,
+ * followed by configuring HPR{B,L}AR.
+ */
+static void prepare_selector(uint8_t *sel)
+{
+    uint8_t cur_sel = *sel;
+    /* The top 24 bits of HPRSELR are RES0. */
+    uint8_t val = READ_SYSREG(HPRSELR) & 0xff;
+
+    if ( (cur_sel > 31) && (cur_sel != val) )
+    {
+        WRITE_SYSREG(cur_sel, HPRSELR);
+        isb();
+    }
+}
+
+void read_protection_region(pr_t *pr_read, uint8_t sel)
+{
+    prepare_selector(&sel);
+
+    switch ( sel )
+    {
+        GENERATE_READ_PR_REG_CASE(0, pr_read);
+        GENERATE_READ_PR_REG_CASE(1, pr_read);
+        GENERATE_READ_PR_REG_CASE(2, pr_read);
+        GENERATE_READ_PR_REG_CASE(3, pr_read);
+        GENERATE_READ_PR_REG_CASE(4, pr_read);
+        GENERATE_READ_PR_REG_CASE(5, pr_read);
+        GENERATE_READ_PR_REG_CASE(6, pr_read);
+        GENERATE_READ_PR_REG_CASE(7, pr_read);
+        GENERATE_READ_PR_REG_CASE(8, pr_read);
+        GENERATE_READ_PR_REG_CASE(9, pr_read);
+        GENERATE_READ_PR_REG_CASE(10, pr_read);
+        GENERATE_READ_PR_REG_CASE(11, pr_read);
+        GENERATE_READ_PR_REG_CASE(12, pr_read);
+        GENERATE_READ_PR_REG_CASE(13, pr_read);
+        GENERATE_READ_PR_REG_CASE(14, pr_read);
+        GENERATE_READ_PR_REG_CASE(15, pr_read);
+        GENERATE_READ_PR_REG_CASE(16, pr_read);
+        GENERATE_READ_PR_REG_CASE(17, pr_read);
+        GENERATE_READ_PR_REG_CASE(18, pr_read);
+        GENERATE_READ_PR_REG_CASE(19, pr_read);
+        GENERATE_READ_PR_REG_CASE(20, pr_read);
+        GENERATE_READ_PR_REG_CASE(21, pr_read);
+        GENERATE_READ_PR_REG_CASE(22, pr_read);
+        GENERATE_READ_PR_REG_CASE(23, pr_read);
+        GENERATE_READ_PR_REG_CASE(24, pr_read);
+        GENERATE_READ_PR_REG_CASE(25, pr_read);
+        GENERATE_READ_PR_REG_CASE(26, pr_read);
+        GENERATE_READ_PR_REG_CASE(27, pr_read);
+        GENERATE_READ_PR_REG_CASE(28, pr_read);
+        GENERATE_READ_PR_REG_CASE(29, pr_read);
+        GENERATE_READ_PR_REG_CASE(30, pr_read);
+        GENERATE_READ_PR_REG_CASE(31, pr_read);
+        GENERATE_READ_PR_REG_OTHERS(32 ... 254, pr_read);
+    default:
+        BUG(); /* Can't happen */
+        break;
+    }
+}
+
+void write_protection_region(const pr_t *pr_write, uint8_t sel)
+{
+    prepare_selector(&sel);
+
+    switch ( sel )
+    {
+        GENERATE_WRITE_PR_REG_CASE(0, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(1, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(2, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(3, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(4, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(5, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(6, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(7, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(8, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(9, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(10, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(11, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(12, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(13, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(14, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(15, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(16, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(17, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(18, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(19, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(20, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(21, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(22, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(23, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(24, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(25, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(26, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(27, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(28, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(29, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(30, pr_write);
+        GENERATE_WRITE_PR_REG_CASE(31, pr_write);
+        GENERATE_WRITE_PR_REG_OTHERS(32 ... 254, pr_write);
+    default:
+        BUG(); /* Can't happen */
+        break;
+    }
+}
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
diff --git a/xen/arch/arm/mpu/mm.c b/xen/arch/arm/mpu/mm.c
index 7ab68fc8c7..ccfb37a67b 100644
--- a/xen/arch/arm/mpu/mm.c
+++ b/xen/arch/arm/mpu/mm.c
@@ -39,7 +39,6 @@ static void __init __maybe_unused build_assertions(void)
      BUILD_BUG_ON(PAGE_SIZE != SZ_4K);
  }
-#ifdef CONFIG_ARM_64 
  pr_t pr_of_addr(paddr_t base, paddr_t limit, unsigned int flags)
  {
      unsigned int attr_idx = PAGE_AI_MASK(flags);
@@ -110,7 +109,6 @@ pr_t pr_of_addr(paddr_t base, paddr_t limit, unsigned int 
flags)
return region; 
  }
-#endif /* CONFIG_ARM_64 */
void __init setup_mm(void) 
  {


--
Julien Grall

 

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