target/arm: Implement helper_mte_checkN

Fill out the stub that was added earlier.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20200626033144.790098-27-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

target/arm/internals.h

@@ -1321,6 +1321,8 @@ FIELD(MTEDESC, TSIZE, 14, 10)  /* mte_checkN only */
 bool mte_probe1(CPUARMState *env, uint32_t desc, uint64_t ptr);
 uint64_t mte_check1(CPUARMState *env, uint32_t desc,
                     uint64_t ptr, uintptr_t ra);
+uint64_t mte_checkN(CPUARMState *env, uint32_t desc,
+                    uint64_t ptr, uintptr_t ra);
 
 static inline int allocation_tag_from_addr(uint64_t ptr)
 {

target/arm/mte_helper.c

@@ -500,7 +500,170 @@ uint64_t HELPER(mte_check1)(CPUARMState *env, uint32_t desc, uint64_t ptr)
 /*
  * Perform an MTE checked access for multiple logical accesses.
  */
+
+/**
+ * checkN:
+ * @tag: tag memory to test
+ * @odd: true to begin testing at tags at odd nibble
+ * @cmp: the tag to compare against
+ * @count: number of tags to test
+ *
+ * Return the number of successful tests.
+ * Thus a return value < @count indicates a failure.
+ *
+ * A note about sizes: count is expected to be small.
+ *
+ * The most common use will be LDP/STP of two integer registers,
+ * which means 16 bytes of memory touching at most 2 tags, but
+ * often the access is aligned and thus just 1 tag.
+ *
+ * Using AdvSIMD LD/ST (multiple), one can access 64 bytes of memory,
+ * touching at most 5 tags.  SVE LDR/STR (vector) with the default
+ * vector length is also 64 bytes; the maximum architectural length
+ * is 256 bytes touching at most 9 tags.
+ *
+ * The loop below uses 7 logical operations and 1 memory operation
+ * per tag pair.  An implementation that loads an aligned word and
+ * uses masking to ignore adjacent tags requires 18 logical operations
+ * and thus does not begin to pay off until 6 tags.
+ * Which, according to the survey above, is unlikely to be common.
+ */
+static int checkN(uint8_t *mem, int odd, int cmp, int count)
+{
+    int n = 0, diff;
+
+    /* Replicate the test tag and compare.  */
+    cmp *= 0x11;
+    diff = *mem++ ^ cmp;
+
+    if (odd) {
+        goto start_odd;
+    }
+
+    while (1) {
+        /* Test even tag. */
+        if (unlikely((diff) & 0x0f)) {
+            break;
+        }
+        if (++n == count) {
+            break;
+        }
+
+    start_odd:
+        /* Test odd tag. */
+        if (unlikely((diff) & 0xf0)) {
+            break;
+        }
+        if (++n == count) {
+            break;
+        }
+
+        diff = *mem++ ^ cmp;
+    }
+    return n;
+}
+
+uint64_t mte_checkN(CPUARMState *env, uint32_t desc,
+                    uint64_t ptr, uintptr_t ra)
+{
+    int mmu_idx, ptr_tag, bit55;
+    uint64_t ptr_last, ptr_end, prev_page, next_page;
+    uint64_t tag_first, tag_end;
+    uint64_t tag_byte_first, tag_byte_end;
+    uint32_t esize, total, tag_count, tag_size, n, c;
+    uint8_t *mem1, *mem2;
+    MMUAccessType type;
+
+    bit55 = extract64(ptr, 55, 1);
+
+    /* If TBI is disabled, the access is unchecked, and ptr is not dirty. */
+    if (unlikely(!tbi_check(desc, bit55))) {
+        return ptr;
+    }
+
+    ptr_tag = allocation_tag_from_addr(ptr);
+
+    if (tcma_check(desc, bit55, ptr_tag)) {
+        goto done;
+    }
+
+    mmu_idx = FIELD_EX32(desc, MTEDESC, MIDX);
+    type = FIELD_EX32(desc, MTEDESC, WRITE) ? MMU_DATA_STORE : MMU_DATA_LOAD;
+    esize = FIELD_EX32(desc, MTEDESC, ESIZE);
+    total = FIELD_EX32(desc, MTEDESC, TSIZE);
+
+    /* Find the addr of the end of the access, and of the last element. */
+    ptr_end = ptr + total;
+    ptr_last = ptr_end - esize;
+
+    /* Round the bounds to the tag granule, and compute the number of tags. */
+    tag_first = QEMU_ALIGN_DOWN(ptr, TAG_GRANULE);
+    tag_end = QEMU_ALIGN_UP(ptr_last, TAG_GRANULE);
+    tag_count = (tag_end - tag_first) / TAG_GRANULE;
+
+    /* Round the bounds to twice the tag granule, and compute the bytes. */
+    tag_byte_first = QEMU_ALIGN_DOWN(ptr, 2 * TAG_GRANULE);
+    tag_byte_end = QEMU_ALIGN_UP(ptr_last, 2 * TAG_GRANULE);
+
+    /* Locate the page boundaries. */
+    prev_page = ptr & TARGET_PAGE_MASK;
+    next_page = prev_page + TARGET_PAGE_SIZE;
+
+    if (likely(tag_end - prev_page <= TARGET_PAGE_SIZE)) {
+        /* Memory access stays on one page. */
+        tag_size = (tag_byte_end - tag_byte_first) / (2 * TAG_GRANULE);
+        mem1 = allocation_tag_mem(env, mmu_idx, ptr, type, total,
+                                  MMU_DATA_LOAD, tag_size, ra);
+        if (!mem1) {
+            goto done;
+        }
+        /* Perform all of the comparisons. */
+        n = checkN(mem1, ptr & TAG_GRANULE, ptr_tag, tag_count);
+    } else {
+        /* Memory access crosses to next page. */
+        tag_size = (next_page - tag_byte_first) / (2 * TAG_GRANULE);
+        mem1 = allocation_tag_mem(env, mmu_idx, ptr, type, next_page - ptr,
+                                  MMU_DATA_LOAD, tag_size, ra);
+
+        tag_size = (tag_byte_end - next_page) / (2 * TAG_GRANULE);
+        mem2 = allocation_tag_mem(env, mmu_idx, next_page, type,
+                                  ptr_end - next_page,
+                                  MMU_DATA_LOAD, tag_size, ra);
+
+        /*
+         * Perform all of the comparisons.
+         * Note the possible but unlikely case of the operation spanning
+         * two pages that do not both have tagging enabled.
+         */
+        n = c = (next_page - tag_first) / TAG_GRANULE;
+        if (mem1) {
+            n = checkN(mem1, ptr & TAG_GRANULE, ptr_tag, c);
+        }
+        if (n == c) {
+            if (!mem2) {
+                goto done;
+            }
+            n += checkN(mem2, 0, ptr_tag, tag_count - c);
+        }
+    }
+
+    /*
+     * If we failed, we know which granule.  Compute the element that
+     * is first in that granule, and signal failure on that element.
+     */
+    if (unlikely(n < tag_count)) {
+        uint64_t fail_ofs;
+
+        fail_ofs = tag_first + n * TAG_GRANULE - ptr;
+        fail_ofs = ROUND_UP(fail_ofs, esize);
+        mte_check_fail(env, mmu_idx, ptr + fail_ofs, ra);
+    }
+
+ done:
+    return useronly_clean_ptr(ptr);
+}
+
 uint64_t HELPER(mte_checkN)(CPUARMState *env, uint32_t desc, uint64_t ptr)
 {
-    return ptr;
+    return mte_checkN(env, desc, ptr, GETPC());
 }