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[PATCH v3 6/6] arm/mpu: Enable read/write to protection regions for arm32


  • To: <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • From: Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>
  • Date: Wed, 11 Jun 2025 15:35:44 +0100
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  • Cc: Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, "Volodymyr Babchuk" <Volodymyr_Babchuk@xxxxxxxx>
  • Delivery-date: Wed, 11 Jun 2025 14:40:55 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

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 255.

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

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

v1 - 1. Enable write_protection_region() for aarch32.

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

 xen/arch/arm/include/asm/mpu.h  |   2 -
 xen/arch/arm/mpu/arm32/Makefile |   1 +
 xen/arch/arm/mpu/arm32/mm.c     | 165 ++++++++++++++++++++++++++++++++
 xen/arch/arm/mpu/mm.c           |   2 -
 4 files changed, 166 insertions(+), 4 deletions(-)
 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/arm32/Makefile b/xen/arch/arm/mpu/arm32/Makefile
index e15ce2f7be..3da872322e 100644
--- a/xen/arch/arm/mpu/arm32/Makefile
+++ b/xen/arch/arm/mpu/arm32/Makefile
@@ -1 +1,2 @@
 obj-y += domain-page.o
+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..5d3cb6dff7
--- /dev/null
+++ b/xen/arch/arm/mpu/arm32/mm.c
@@ -0,0 +1,165 @@
+/* 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 PRBAR_EL2_(n)   HPRBAR##n
+#define PRLAR_EL2_(n)   HPRLAR##n
+
+#define GENERATE_WRITE_PR_REG_CASE(num, pr)                                 \
+    case num:                                                               \
+    {                                                                       \
+        WRITE_SYSREG(pr->prbar.bits & ~MPU_REGION_RES0, PRBAR_EL2_(num));   \
+        WRITE_SYSREG(pr->prlar.bits & ~MPU_REGION_RES0, PRLAR_EL2_(num));   \
+        break;                                                              \
+    }
+
+#define GENERATE_WRITE_PR_REG_OTHERS(num, pr)                               \
+    case num:                                                               \
+    {                                                                       \
+        WRITE_SYSREG(pr->prbar.bits & ~MPU_REGION_RES0, HPRBAR);            \
+        WRITE_SYSREG(pr->prlar.bits & ~MPU_REGION_RES0, HPRLAR);            \
+        break;                                                              \
+    }
+
+#define GENERATE_READ_PR_REG_CASE(num, pr)                                  \
+    case num:                                                               \
+    {                                                                       \
+        pr->prbar.bits = READ_SYSREG(PRBAR_EL2_(num));                      \
+        pr->prlar.bits = READ_SYSREG(PRLAR_EL2_(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 PR{B,L}AR<n>_ELx (for n=0..31) are used for direct access to 
the
+ * first 32 MPU regions.
+ * For MPU region numbered 32..255, one need to set the region number in 
PRSELR_ELx,
+ * followed by configuring PR{B,L}AR_ELx.
+ */
+inline void prepare_selector(uint8_t *sel)
+{
+    uint8_t cur_sel = *sel;
+
+    if ( cur_sel > 0x1FU )
+    {
+        WRITE_SYSREG(cur_sel, PRSELR_EL2);
+        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 ... 255, 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 ... 255, 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)
 {
-- 
2.25.1




 


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