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Re: [PATCH v3 3/5] arm/mpu: Implement transient mapping
Hi,
On 28/08/2025 12:12, 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>
Reviewed-by: Michal Orzel <michal.orzel@xxxxxxx>
---
Changes from v2:
- Define offsets programmatically, rather than hard-coding these
- Add Michal's R-b
Changes from v1:
- Improve commit message
- Mark parameter in read helper as const
---
xen/arch/arm/arm32/asm-offsets.c | 3 ++-
xen/arch/arm/arm64/asm-offsets.c | 2 ++
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 | 17 +++++++++++++----
xen/arch/arm/mpu/mm.c | 23 ++++++++++++++---------
7 files changed, 48 insertions(+), 15 deletions(-)
diff --git a/xen/arch/arm/arm32/asm-offsets.c b/xen/arch/arm/arm32/asm-offsets.c
index c203ce269d..f354bf374d 100644
--- a/xen/arch/arm/arm32/asm-offsets.c
+++ b/xen/arch/arm/arm32/asm-offsets.c
@@ -43,7 +43,6 @@ void __dummy__(void)
OFFSET(UREGS_SP_und, struct cpu_user_regs, sp_und);
OFFSET(UREGS_LR_und, struct cpu_user_regs, lr_und);
OFFSET(UREGS_SPSR_und, struct cpu_user_regs, spsr_und);
-
Spurious change?
OFFSET(UREGS_SP_irq, struct cpu_user_regs, sp_irq);
OFFSET(UREGS_LR_irq, struct cpu_user_regs, lr_irq);
OFFSET(UREGS_SPSR_irq, struct cpu_user_regs, spsr_irq);
@@ -79,6 +78,8 @@ void __dummy__(void)
#ifdef CONFIG_MPU
DEFINE(XEN_MPUMAP_MASK_sizeof, sizeof(xen_mpumap_mask));
DEFINE(XEN_MPUMAP_sizeof, sizeof(xen_mpumap));
+ DEFINE(XEN_MPUMAP_ENTRY_SHIFT, ilog2(sizeof(pr_t)));
+ DEFINE(XEN_MPUMAP_ENTRY_ZERO_OFFSET, sizeof(prbar_t) + sizeof(prlar_t));
BLANK();
#endif
}
diff --git a/xen/arch/arm/arm64/asm-offsets.c b/xen/arch/arm/arm64/asm-offsets.c
index 320289b281..38a3894a3b 100644
--- a/xen/arch/arm/arm64/asm-offsets.c
+++ b/xen/arch/arm/arm64/asm-offsets.c
@@ -73,6 +73,8 @@ void __dummy__(void)
#ifdef CONFIG_MPU
DEFINE(XEN_MPUMAP_MASK_sizeof, sizeof(xen_mpumap_mask));
DEFINE(XEN_MPUMAP_sizeof, sizeof(xen_mpumap));
+ DEFINE(XEN_MPUMAP_ENTRY_SHIFT, ilog2(sizeof(pr_t)));
+ DEFINE(XEN_MPUMAP_ENTRY_ZERO_OFFSET, sizeof(prbar_t) + sizeof(prlar_t));
BLANK();
#endif
}
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 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.
Why can't this be part of the flags?
* @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..09e1dcf03f 100644
--- a/xen/arch/arm/include/asm/mpu/regions.inc
+++ b/xen/arch/arm/include/asm/mpu/regions.inc
@@ -14,19 +14,25 @@
#define PRLAR_ELx_EN 0x1
#ifdef CONFIG_ARM_64
-#define XEN_MPUMAP_ENTRY_SHIFT 0x4 /* 16 byte structure */
-
.macro store_pair reg1, reg2, dst
stp \reg1, \reg2, [\dst]
.endm
-#else
-#define XEN_MPUMAP_ENTRY_SHIFT 0x3 /* 8 byte structure */
+.macro zero_pair dst, offset, tmp1, tmp2
> + stp xzr, xzr, [\dst, \offset]> +.endm
+#else
.macro store_pair reg1, reg2, dst
strd \reg1, \reg2, [\dst]
.endm
+.macro zero_pair dst, offset, tmp1, tmp2
+ mov \tmp1, #0
+ mov \tmp2, #0
+ strd \tmp1, \tmp2, [\dst, \offset]
+.endm
> +
TBH the addition of zero_pair feels a bit overkill when there is one
user. Why can't we open-code the use case below and use ``store_pair``?
This would also avoid the "tmp1" and "tmp2" which are not used by arm64.
Cheers,
--
Julien Grall
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