| Message ID | 20241025175857.2554252-2-pierrick.bouvier@linaro.org |
|---|---|
| State | New |
| Headers | show |
| Series | target/i386: fix hang when using slow path for ptw_setl | expand |
On 10/25/24 18:58, Pierrick Bouvier wrote: > 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 > [3]https://gitlab.com/qemu-project/qemu/-/issues/279 > > Fixes:https://gitlab.com/qemu-project/qemu/-/issues/2566 > Signed-off-by: Pierrick Bouvier<pierrick.bouvier@linaro.org> > --- > target/i386/tcg/sysemu/excp_helper.c | 5 +++++ > 1 file changed, 5 insertions(+) Reviewed-by: Richard Henderson <richard.henderson@linaro.org> r~
diff --git a/target/i386/tcg/sysemu/excp_helper.c b/target/i386/tcg/sysemu/excp_helper.c index da187c8792a..ddc51e3e0b8 100644 --- a/target/i386/tcg/sysemu/excp_helper.c +++ b/target/i386/tcg/sysemu/excp_helper.c @@ -107,6 +107,10 @@ 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); @@ -114,6 +118,7 @@ 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; }
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 [3] https://gitlab.com/qemu-project/qemu/-/issues/279 Fixes: https://gitlab.com/qemu-project/qemu/-/issues/2566 Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org> --- target/i386/tcg/sysemu/excp_helper.c | 5 +++++ 1 file changed, 5 insertions(+)