target/riscv: fix endless translation loop on big endian systems

On big endian systems, pte and updated_pte hold big endian host data
while pte_pa points to little endian target data. This means the branch
at cpu_helper.c:1669 will be always satisfied and restart translation,
causing an endless translation loop.

The correctness of this patch can be deduced by:

old_pte will hold value either from cpu_to_le32/64(pte) or
cpu_to_le32/64(updated_pte), both of wich is litte endian. After that,
an in-place conversion by le32/64_to_cpu(old_pte) ensures that old_pte
now is in native endian, same with pte. Therefore, the endianness of the
both side of if (old_pte != pte) is correct.

Signed-off-by: Ziqiao Kong <ziqiaokong@gmail.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <20250415080254.3667878-2-ziqiaokong@gmail.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Cc: qemu-stable@nongnu.org
(cherry picked from commit ad63158bdb33dab5704ea1cf740d2ea0387175df)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
index dfd6a9d14924e0310a1ae9b50df5d2accc666a30..803d87479c2a0880caeadbc1fbd3e62f60c496c2 100644 (file)
--- a/target/riscv/cpu_helper.c
+++ b/target/riscv/cpu_helper.c
@@ -1240,9 +1240,11 @@ restart:
 #else
             target_ulong old_pte;
             if (riscv_cpu_sxl(env) == MXL_RV32) {
-                old_pte = qatomic_cmpxchg((uint32_t *)pte_pa, pte, updated_pte);
+                old_pte = qatomic_cmpxchg((uint32_t *)pte_pa, cpu_to_le32(pte), cpu_to_le32(updated_pte));
+                old_pte = le32_to_cpu(old_pte);
             } else {
-                old_pte = qatomic_cmpxchg(pte_pa, pte, updated_pte);
+                old_pte = qatomic_cmpxchg(pte_pa, cpu_to_le64(pte), cpu_to_le64(updated_pte));
+                old_pte = le64_to_cpu(old_pte);
             }
             if (old_pte != pte) {
                 goto restart;