[PULL 36/42] target/arm: Move mte check for store-exclusive

From: Peter Maydell <peter.maydell@linaro.org>
To: qemu-devel@nongnu.org
Subject: [PULL 36/42] target/arm: Move mte check for store-exclusive
Date: Tue,  6 Jun 2023 10:48:08 +0100	[thread overview]
Message-ID: <20230606094814.3581397-37-peter.maydell@linaro.org> (raw)
In-Reply-To: <20230606094814.3581397-1-peter.maydell@linaro.org>

From: Richard Henderson <richard.henderson@linaro.org>

Push the mte check behind the exclusive_addr check.
Document the several ways that we are still out of spec
with this implementation.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20230530191438.411344-18-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 target/arm/tcg/translate-a64.c | 42 +++++++++++++++++++++++++++++-----
 1 file changed, 36 insertions(+), 6 deletions(-)

diff --git a/target/arm/tcg/translate-a64.c b/target/arm/tcg/translate-a64.c
index adedebd1c22..aa93f37e216 100644
--- a/target/arm/tcg/translate-a64.c
+++ b/target/arm/tcg/translate-a64.c
@@ -2512,17 +2512,47 @@ static void gen_store_exclusive(DisasContext *s, int rd, int rt, int rt2,
      */
     TCGLabel *fail_label = gen_new_label();
     TCGLabel *done_label = gen_new_label();
-    TCGv_i64 tmp, dirty_addr, clean_addr;
+    TCGv_i64 tmp, clean_addr;
     MemOp memop;
 
-    memop = (size + is_pair) | MO_ALIGN;
-    memop = finalize_memop(s, memop);
-
-    dirty_addr = cpu_reg_sp(s, rn);
-    clean_addr = gen_mte_check1(s, dirty_addr, true, rn != 31, memop);
+    /*
+     * FIXME: We are out of spec here.  We have recorded only the address
+     * from load_exclusive, not the entire range, and we assume that the
+     * size of the access on both sides match.  The architecture allows the
+     * store to be smaller than the load, so long as the stored bytes are
+     * within the range recorded by the load.
+     */
 
+    /* See AArch64.ExclusiveMonitorsPass() and AArch64.IsExclusiveVA(). */
+    clean_addr = clean_data_tbi(s, cpu_reg_sp(s, rn));
     tcg_gen_brcond_i64(TCG_COND_NE, clean_addr, cpu_exclusive_addr, fail_label);
 
+    /*
+     * The write, and any associated faults, only happen if the virtual
+     * and physical addresses pass the exclusive monitor check.  These
+     * faults are exceedingly unlikely, because normally the guest uses
+     * the exact same address register for the load_exclusive, and we
+     * would have recognized these faults there.
+     *
+     * It is possible to trigger an alignment fault pre-LSE2, e.g. with an
+     * unaligned 4-byte write within the range of an aligned 8-byte load.
+     * With LSE2, the store would need to cross a 16-byte boundary when the
+     * load did not, which would mean the store is outside the range
+     * recorded for the monitor, which would have failed a corrected monitor
+     * check above.  For now, we assume no size change and retain the
+     * MO_ALIGN to let tcg know what we checked in the load_exclusive.
+     *
+     * It is possible to trigger an MTE fault, by performing the load with
+     * a virtual address with a valid tag and performing the store with the
+     * same virtual address and a different invalid tag.
+     */
+    memop = size + is_pair;
+    if (memop == MO_128 || !dc_isar_feature(aa64_lse2, s)) {
+        memop |= MO_ALIGN;
+    }
+    memop = finalize_memop(s, memop);
+    gen_mte_check1(s, cpu_reg_sp(s, rn), true, rn != 31, memop);
+
     tmp = tcg_temp_new_i64();
     if (is_pair) {
         if (size == 2) {
-- 
2.34.1


