Implement reference counting to enable inclusive MPU regions. An
inclusive region is defined as a region encapsulated inside a
previously allocated region sharing the same permissions.
References are incremented and decremented in xen_mpumap_update_entry. A
region will be destroyed if the reference count is 0 upon calling
destroy_xen_mappings and if the full region range is specified.
Additionally XEN_MPUMAP_ENTRY_SHIFT and XEN_MPUMAP_ENTRY_SHIFT_ZERO are
no longer hardcoded and defined inside asm-offsets.c.
Signed-off-by: Harry Ramsey <harry.ramsey@arm.com>
---
Changes in v2:
- Improve clarity with regards to MPU inclusive regions
- Fix code format issues
---
xen/arch/arm/arm32/asm-offsets.c | 2 +
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/regions.inc | 11 +++-
xen/arch/arm/mpu/mm.c | 75 +++++++++++++++++++-----
6 files changed, 78 insertions(+), 16 deletions(-)
diff --git a/xen/arch/arm/arm32/asm-offsets.c b/xen/arch/arm/arm32/asm-offsets.c
index c203ce269d..951f8d03f3 100644
--- a/xen/arch/arm/arm32/asm-offsets.c
+++ b/xen/arch/arm/arm32/asm-offsets.c
@@ -79,6 +79,8 @@ 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..137022d922 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;
+ uint8_t refcount;
+ 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..17f62ccaf6 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;
+ uint8_t refcount;
+ uint8_t pad[15]; /* Pad structure to 32 Bytes */
} pr_t;
#endif /* __ASSEMBLY__ */
diff --git a/xen/arch/arm/include/asm/mpu/regions.inc b/xen/arch/arm/include/asm/mpu/regions.inc
index 23fead3b21..0cdbb17bc3 100644
--- a/xen/arch/arm/include/asm/mpu/regions.inc
+++ b/xen/arch/arm/include/asm/mpu/regions.inc
@@ -14,14 +14,12 @@
#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 store_pair reg1, reg2, dst
strd \reg1, \reg2, [\dst]
@@ -97,6 +95,15 @@
3:
+ /* Clear the rest of the xen_mpumap entry. */
+#ifdef CONFIG_ARM_64
+ stp xzr, xzr, [\base, #XEN_MPUMAP_ENTRY_ZERO_OFFSET]
+#else
+ mov \prbar, #0
+ mov \prlar, #0
+ strd \prbar, \prlar, [\base, #XEN_MPUMAP_ENTRY_ZERO_OFFSET]
+#endif
+
add \sel, \sel, #1
1:
diff --git a/xen/arch/arm/mpu/mm.c b/xen/arch/arm/mpu/mm.c
index b80edcf1ca..cd84f9e3c6 100644
--- a/xen/arch/arm/mpu/mm.c
+++ b/xen/arch/arm/mpu/mm.c
@@ -106,6 +106,7 @@ pr_t pr_of_addr(paddr_t base, paddr_t limit, unsigned int flags)
region = (pr_t) {
.prbar = prbar,
.prlar = prlar,
+ .refcount = 0,
};
/* Set base address and limit address. */
@@ -170,6 +171,37 @@ int mpumap_contains_region(pr_t *table, uint8_t nr_regions, paddr_t base,
return MPUMAP_REGION_NOTFOUND;
}
+static bool is_mm_attr_match(pr_t *region, unsigned int attributes)
+{
+ bool ret = true;
+
+ if ( region->prbar.reg.ro != PAGE_RO_MASK(attributes) )
+ {
+ printk(XENLOG_WARNING
+ "Mismatched Access Permission attributes (%#x instead of %#x)\n",
+ region->prbar.reg.ro, PAGE_RO_MASK(attributes));
+ ret = false;
+ }
+
+ if ( region->prbar.reg.xn != PAGE_XN_MASK(attributes) )
+ {
+ printk(XENLOG_WARNING
+ "Mismatched Execute Never attributes (%#x instead of %#x)\n",
+ region->prbar.reg.xn, PAGE_XN_MASK(attributes));
+ ret = false;
+ }
+
+ if ( region->prlar.reg.ai != PAGE_AI_MASK(attributes) )
+ {
+ printk(XENLOG_WARNING
+ "Mismatched Memory Attribute Index (%#x instead of %#x)\n",
+ region->prlar.reg.ai, PAGE_AI_MASK(attributes));
+ ret = false;
+ }
+
+ return ret;
+}
+
/* Map a frame table to cover physical addresses ps through pe */
void __init setup_frametable_mappings(paddr_t ps, paddr_t pe)
{
@@ -284,22 +316,26 @@ static int xen_mpumap_update_entry(paddr_t base, paddr_t limit,
flags_has_page_present = flags & _PAGE_PRESENT;
- /* Currently we don't support modifying an existing entry. */
+ /*
+ * Currently, we only support removing/modifying a *WHOLE* MPU memory
+ * region. Part-region removal/modification is not supported as in the worst
+ * case it will leave two/three fragments behind.
+ */
if ( flags_has_page_present && (rc >= MPUMAP_REGION_FOUND) )
{
- printk("Modifying an existing entry is not supported\n");
- return -EINVAL;
- }
+ if ( !is_mm_attr_match(&xen_mpumap[idx], flags) )
+ {
+ printk("Modifying an existing entry is not supported\n");
+ return -EINVAL;
+ }
- /*
- * Currently, we only support removing/modifying a *WHOLE* MPU memory
- * region. Part-region removal/modification is not supported as in the worst
- * case it will leave two/three fragments behind.
- */
- if ( rc == MPUMAP_REGION_INCLUSIVE )
- {
- printk("Part-region removal/modification is not supported\n");
- return -EINVAL;
+ /* Check for overflow of refcount before incrementing. */
+ if ( xen_mpumap[idx].refcount == 0xFF )
+ {
+ printk("Cannot allocate region as it would cause reference overflow\n");
+ return -ENOENT;
+ }
+ xen_mpumap[idx].refcount += 1;
}
/* We are inserting a mapping => Create new region. */
@@ -323,7 +359,18 @@ static int xen_mpumap_update_entry(paddr_t base, paddr_t limit,
return -EINVAL;
}
- disable_mpu_region_from_index(idx);
+ if ( xen_mpumap[idx].refcount == 0 )
+ {
+ if ( MPUMAP_REGION_FOUND == rc )
+ disable_mpu_region_from_index(idx);
+ else
+ {
+ printk("Cannot remove a partial region\n");
+ return -EINVAL;
+ }
+ }
+ else
+ xen_mpumap[idx].refcount -= 1;
}
return 0;
--
2.43.0
On 11/11/2025 11:16, Harry Ramsey wrote:
> Implement reference counting to enable inclusive MPU regions. An
> inclusive region is defined as a region encapsulated inside a
> previously allocated region sharing the same permissions.
>
> References are incremented and decremented in xen_mpumap_update_entry. A
> region will be destroyed if the reference count is 0 upon calling
> destroy_xen_mappings and if the full region range is specified.
>
> Additionally XEN_MPUMAP_ENTRY_SHIFT and XEN_MPUMAP_ENTRY_SHIFT_ZERO are
> no longer hardcoded and defined inside asm-offsets.c.
>
> Signed-off-by: Harry Ramsey <harry.ramsey@arm.com>
> ---
> Changes in v2:
> - Improve clarity with regards to MPU inclusive regions
> - Fix code format issues
> ---
> xen/arch/arm/arm32/asm-offsets.c | 2 +
> 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/regions.inc | 11 +++-
> xen/arch/arm/mpu/mm.c | 75 +++++++++++++++++++-----
> 6 files changed, 78 insertions(+), 16 deletions(-)
>
> diff --git a/xen/arch/arm/arm32/asm-offsets.c b/xen/arch/arm/arm32/asm-offsets.c
> index c203ce269d..951f8d03f3 100644
> --- a/xen/arch/arm/arm32/asm-offsets.c
> +++ b/xen/arch/arm/arm32/asm-offsets.c
> @@ -79,6 +79,8 @@ 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..137022d922 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;
> + uint8_t refcount;
> + 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..17f62ccaf6 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;
> + uint8_t refcount;
> + uint8_t pad[15]; /* Pad structure to 32 Bytes */
> } pr_t;
>
> #endif /* __ASSEMBLY__ */
> diff --git a/xen/arch/arm/include/asm/mpu/regions.inc b/xen/arch/arm/include/asm/mpu/regions.inc
> index 23fead3b21..0cdbb17bc3 100644
> --- a/xen/arch/arm/include/asm/mpu/regions.inc
> +++ b/xen/arch/arm/include/asm/mpu/regions.inc
> @@ -14,14 +14,12 @@
> #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 store_pair reg1, reg2, dst
> strd \reg1, \reg2, [\dst]
> @@ -97,6 +95,15 @@
>
> 3:
>
> + /* Clear the rest of the xen_mpumap entry. */
> +#ifdef CONFIG_ARM_64
> + stp xzr, xzr, [\base, #XEN_MPUMAP_ENTRY_ZERO_OFFSET]
> +#else
> + mov \prbar, #0
> + mov \prlar, #0
> + strd \prbar, \prlar, [\base, #XEN_MPUMAP_ENTRY_ZERO_OFFSET]
> +#endif
> +
> add \sel, \sel, #1
>
> 1:
> diff --git a/xen/arch/arm/mpu/mm.c b/xen/arch/arm/mpu/mm.c
> index b80edcf1ca..cd84f9e3c6 100644
> --- a/xen/arch/arm/mpu/mm.c
> +++ b/xen/arch/arm/mpu/mm.c
> @@ -106,6 +106,7 @@ pr_t pr_of_addr(paddr_t base, paddr_t limit, unsigned int flags)
> region = (pr_t) {
> .prbar = prbar,
> .prlar = prlar,
> + .refcount = 0,
> };
>
> /* Set base address and limit address. */
> @@ -170,6 +171,37 @@ int mpumap_contains_region(pr_t *table, uint8_t nr_regions, paddr_t base,
> return MPUMAP_REGION_NOTFOUND;
> }
>
> +static bool is_mm_attr_match(pr_t *region, unsigned int attributes)
> +{
> + bool ret = true;
> +
> + if ( region->prbar.reg.ro != PAGE_RO_MASK(attributes) )
> + {
> + printk(XENLOG_WARNING
> + "Mismatched Access Permission attributes (%#x instead of %#x)\n",
> + region->prbar.reg.ro, PAGE_RO_MASK(attributes));
> + ret = false;
NIT: I think it's more clear when you return false here. Otherwise after setting
ret to false, what's the point for checking additionally for below conditions?
> + }
> +
> + if ( region->prbar.reg.xn != PAGE_XN_MASK(attributes) )
> + {
> + printk(XENLOG_WARNING
> + "Mismatched Execute Never attributes (%#x instead of %#x)\n",
> + region->prbar.reg.xn, PAGE_XN_MASK(attributes));
> + ret = false;
> + }
> +
> + if ( region->prlar.reg.ai != PAGE_AI_MASK(attributes) )
> + {
> + printk(XENLOG_WARNING
> + "Mismatched Memory Attribute Index (%#x instead of %#x)\n",
> + region->prlar.reg.ai, PAGE_AI_MASK(attributes));
> + ret = false;
> + }
> +
> + return ret;
> +}
> +
> /* Map a frame table to cover physical addresses ps through pe */
> void __init setup_frametable_mappings(paddr_t ps, paddr_t pe)
> {
> @@ -284,22 +316,26 @@ static int xen_mpumap_update_entry(paddr_t base, paddr_t limit,
>
> flags_has_page_present = flags & _PAGE_PRESENT;
>
> - /* Currently we don't support modifying an existing entry. */
> + /*
> + * Currently, we only support removing/modifying a *WHOLE* MPU memory
> + * region. Part-region removal/modification is not supported as in the worst
> + * case it will leave two/three fragments behind.
> + */
> if ( flags_has_page_present && (rc >= MPUMAP_REGION_FOUND) )
> {
> - printk("Modifying an existing entry is not supported\n");
> - return -EINVAL;
> - }
> + if ( !is_mm_attr_match(&xen_mpumap[idx], flags) )
> + {
> + printk("Modifying an existing entry is not supported\n");
> + return -EINVAL;
> + }
>
> - /*
> - * Currently, we only support removing/modifying a *WHOLE* MPU memory
> - * region. Part-region removal/modification is not supported as in the worst
> - * case it will leave two/three fragments behind.
> - */
> - if ( rc == MPUMAP_REGION_INCLUSIVE )
> - {
> - printk("Part-region removal/modification is not supported\n");
> - return -EINVAL;
> + /* Check for overflow of refcount before incrementing. */
> + if ( xen_mpumap[idx].refcount == 0xFF )
> + {
> + printk("Cannot allocate region as it would cause reference overflow\n");
s/reference/reference count or refcount/
Reviewed-by: Michal Orzel <michal.orzel@amd.com>
~Michal
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