From: Pierrick Bouvier <pierrick.bouv...@linaro.org> When instrumenting memory accesses for plugin, we force memory accesses to use the slow path for mmu [1]. This create a situation where we end up calling ptw_setl_slow. This was fixed recently in [2] but the issue still could appear out of plugins use case.
Since this function gets called during a cpu_exec, start_exclusive then hangs. This exclusive section was introduced initially for security reasons [3]. I suspect this code path was never triggered, because ptw_setl_slow would always be called transitively from cpu_exec, resulting in a hang. [1] https://gitlab.com/qemu-project/qemu/-/commit/6d03226b42247b68ab2f0b3663e0f624335a4055 [2] https://gitlab.com/qemu-project/qemu/-/commit/115ade42d50144c15b74368d32dc734ea277d853 [2] https://gitlab.com/qemu-project/qemu/-/commit/88442869cf709f885a9c09fad00b96f802d58ffe in 9.0.x series [3] https://gitlab.com/qemu-project/qemu/-/issues/279 Fixes: https://gitlab.com/qemu-project/qemu/-/issues/2566 Signed-off-by: Pierrick Bouvier <pierrick.bouv...@linaro.org> Reviewed-by: Richard Henderson <richard.hender...@linaro.org> Message-ID: <20241025175857.2554252-2-pierrick.bouv...@linaro.org> Signed-off-by: Richard Henderson <richard.hender...@linaro.org> (cherry picked from commit 7ba055b49b74c4d2f4a338c5198485bdff373fb1) Signed-off-by: Michael Tokarev <m...@tls.msk.ru> (Mjt: mention [2] in 9.0.x series) diff --git a/target/i386/tcg/sysemu/excp_helper.c b/target/i386/tcg/sysemu/excp_helper.c index bdf7b0df42..44b1b2ded6 100644 --- a/target/i386/tcg/sysemu/excp_helper.c +++ b/target/i386/tcg/sysemu/excp_helper.c @@ -106,6 +106,10 @@ static bool ptw_setl_slow(const PTETranslate *in, uint32_t old, uint32_t new) { uint32_t cmp; + CPUState *cpu = env_cpu(in->env); + /* We are in cpu_exec, and start_exclusive can't be called directly.*/ + g_assert(cpu->running); + cpu_exec_end(cpu); /* Does x86 really perform a rmw cycle on mmio for ptw? */ start_exclusive(); cmp = cpu_ldl_mmuidx_ra(in->env, in->gaddr, in->ptw_idx, 0); @@ -113,6 +117,7 @@ static bool ptw_setl_slow(const PTETranslate *in, uint32_t old, uint32_t new) cpu_stl_mmuidx_ra(in->env, in->gaddr, new, in->ptw_idx, 0); } end_exclusive(); + cpu_exec_start(cpu); return cmp == old; } -- 2.39.5
