[PATCH v3 2/3] target/arm: Add allocation tag storage for user mode

[Richard Henderson <richard.henderson@linaro.org>]

Control this with x-tagged-pages, which is off by default.

The limitation to non-shared pages is not part of a future kernel API,
but a limitation of linux-user not being able to map virtual pages back
to physical pages.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
v2: Add the x-tagged-pages cpu property
---
 target/arm/cpu.h        |  4 ++++
 target/arm/cpu64.c      | 20 ++++++++++++++++++++
 target/arm/mte_helper.c | 35 +++++++++++++++++++++++++++++++++--
 3 files changed, 57 insertions(+), 2 deletions(-)

diff --git a/target/arm/cpu.h b/target/arm/cpu.h
index c3609ef9d5..272df43d3c 100644
--- a/target/arm/cpu.h
+++ b/target/arm/cpu.h
@@ -912,6 +912,10 @@ struct ARMCPU {
      */
     bool cfgend;
 
+#ifdef CONFIG_USER_ONLY
+    bool tagged_pages;
+#endif
+
     QLIST_HEAD(, ARMELChangeHook) pre_el_change_hooks;
     QLIST_HEAD(, ARMELChangeHook) el_change_hooks;
 
diff --git a/target/arm/cpu64.c b/target/arm/cpu64.c
index ac1e2dc2c4..4bf498f778 100644
--- a/target/arm/cpu64.c
+++ b/target/arm/cpu64.c
@@ -279,6 +279,20 @@ static void cpu_max_set_sve_vq(Object *obj, Visitor *v, const char *name,
     error_propagate(errp, err);
 }
 
+#ifdef CONFIG_USER_ONLY
+static bool aarch64_cpu_get_tagged_pages(Object *obj, Error **errp)
+{
+    ARMCPU *cpu = ARM_CPU(obj);
+    return cpu->tagged_pages;
+}
+
+static void aarch64_cpu_set_tagged_pages(Object *obj, bool val, Error **errp)
+{
+    ARMCPU *cpu = ARM_CPU(obj);
+    cpu->tagged_pages = val;
+}
+#endif
+
 /* -cpu max: if KVM is enabled, like -cpu host (best possible with this host);
  * otherwise, a CPU with as many features enabled as our emulation supports.
  * The version of '-cpu max' for qemu-system-arm is defined in cpu.c;
@@ -389,6 +403,12 @@ static void aarch64_max_initfn(Object *obj)
          */
         cpu->ctr = 0x80038003; /* 32 byte I and D cacheline size, VIPT icache */
         cpu->dcz_blocksize = 7; /*  512 bytes */
+
+        object_property_add_bool(obj, "x-tagged-pages",
+                                 aarch64_cpu_get_tagged_pages,
+                                 aarch64_cpu_set_tagged_pages, NULL);
+        object_property_set_description(obj, "x-tagged-pages",
+            "Set on/off MemAttr Tagged for all pages", NULL);
 #endif
 
         cpu->sve_max_vq = ARM_MAX_VQ;
diff --git a/target/arm/mte_helper.c b/target/arm/mte_helper.c
index 657383ba0e..797c6229ab 100644
--- a/target/arm/mte_helper.c
+++ b/target/arm/mte_helper.c
@@ -29,8 +29,39 @@ static uint8_t *allocation_tag_mem(CPUARMState *env, uint64_t ptr,
                                    bool write, uintptr_t ra)
 {
 #ifdef CONFIG_USER_ONLY
-    /* Tag storage not implemented.  */
-    return NULL;
+    ARMCPU *cpu = env_archcpu(env);
+    uint8_t *tags;
+    uintptr_t index;
+    int flags;
+
+    flags = page_get_flags(ptr);
+
+    if (!(flags & PAGE_VALID) || !(flags & (write ? PAGE_WRITE : PAGE_READ))) {
+        /* SIGSEGV */
+        env->exception.vaddress = ptr;
+        cpu_restore_state(CPU(cpu), ra, true);
+        raise_exception(env, EXCP_DATA_ABORT, 0, 1);
+    }
+
+    if (!cpu->tagged_pages) {
+        /* Tag storage is disabled.  */
+        return NULL;
+    }
+    if (flags & PAGE_SHARED) {
+        /* There may be multiple mappings; pretend not implemented.  */
+        return NULL;
+    }
+
+    tags = page_get_target_data(ptr);
+    if (tags == NULL) {
+        size_t alloc_size = TARGET_PAGE_SIZE >> (LOG2_TAG_GRANULE + 1);
+        tags = page_alloc_target_data(ptr, alloc_size);
+        assert(tags != NULL);
+    }
+
+    index = extract32(ptr, LOG2_TAG_GRANULE + 1,
+                      TARGET_PAGE_BITS - LOG2_TAG_GRANULE - 1);
+    return tags + index;
 #else
     CPUState *cs = env_cpu(env);
     uintptr_t index;
-- 
2.17.1