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Tue, 15 Apr 2025 01:03:06 -0700 (PDT) Received: from station.lan ([155.69.190.63]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-306dd12b5c5sm12640745a91.24.2025.04.15.01.03.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 15 Apr 2025 01:03:05 -0700 (PDT) From: Ziqiao Kong To: qemu-devel@nongnu.org Cc: ziqiaokong@gmail.com, qemu-trivial@nongnu.org, alistair.francis@wdc.com, richard.henderson@linaro.org, philmd@linaro.org, pbonzini@redhat.com Subject: [PATCH v3 1/1] target/riscv: fix endless translation loop on big endian systems Date: Tue, 15 Apr 2025 16:02:54 +0800 Message-Id: <20250415080254.3667878-2-ziqiaokong@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20250415080254.3667878-1-ziqiaokong@gmail.com> References: <20250415080254.3667878-1-ziqiaokong@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2607:f8b0:4864:20::532; envelope-from=ziqiaokong@gmail.com; helo=mail-pg1-x532.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FROM=0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org 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 --- target/riscv/cpu_helper.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c index 6c4391d96b..3233b66e7e 100644 --- a/target/riscv/cpu_helper.c +++ b/target/riscv/cpu_helper.c @@ -1662,9 +1662,11 @@ static int get_physical_address(CPURISCVState *env, hwaddr *physical, target_ulong *pte_pa = qemu_map_ram_ptr(mr->ram_block, addr1); 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; -- 2.34.1