On Mon, Jan 04, 2021 at 07:39:13PM +0100, Alexander Graf wrote: > > On 04.01.21 16:23, Alex Bennée wrote: > > Roman Bolshakov <r.bolsha...@yadro.com> writes: > > > > > Pages can't be both write and executable at the same time on Apple > > > Silicon. macOS provides public API to switch write protection [1] for > > > JIT applications, like TCG. > > > > > > 1. > > > https://developer.apple.com/documentation/apple_silicon/porting_just-in-time_compilers_to_apple_silicon > > > > > > Signed-off-by: Roman Bolshakov <r.bolsha...@yadro.com> > > > --- > > > v1: https://lists.gnu.org/archive/html/qemu-devel/2021-01/msg00073.html > > > Changes since v1: > > > > > > - Pruned not needed fiddling with W^X and dropped symmetry from write > > > lock/unlock and renamed related functions. > > > Similar approach is used in JavaScriptCore [1]. > > > > > > - Moved jit helper functions to util/osdep > > > > > > > > > As outlined in osdep.h, this matches to (2): > > > > > > > > > * In an > > > ideal world this header would contain only: > > > * (1) > > > things which everybody needs > > > * (2) > > > things without which code would work on most platforms but > > > * fail > > > to compile or misbehave on a minority of host OSes > > > > > > - Fixed a checkpatch error > > > > > > - Limit new behaviour only to macOS 11.0 and above, because of the > > > following declarations: > > > > > > __API_AVAILABLE(macos(11.0)) > > > __API_UNAVAILABLE(ios, tvos, watchos) > > > void pthread_jit_write_protect_np(int enabled); > > > > > > __API_AVAILABLE(macos(11.0)) > > > __API_UNAVAILABLE(ios, tvos, watchos) > > > int pthread_jit_write_protect_supported_np(void); > > > > > > 1. https://bugs.webkit.org/attachment.cgi?id=402515&action=prettypatch > > > > > > accel/tcg/cpu-exec.c | 2 ++ > > > accel/tcg/translate-all.c | 6 ++++++ > > > include/qemu/osdep.h | 3 +++ > > > tcg/tcg.c | 1 + > > > util/osdep.c | 22 ++++++++++++++++++++++ > > > 5 files changed, 34 insertions(+) > > > > > > diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c > > > index 8689c54499..374060eb45 100644 > > > --- a/accel/tcg/cpu-exec.c > > > +++ b/accel/tcg/cpu-exec.c > > > @@ -175,6 +175,7 @@ static inline tcg_target_ulong cpu_tb_exec(CPUState > > > *cpu, TranslationBlock *itb) > > > } > > > #endif /* DEBUG_DISAS */ > > > + qemu_thread_jit_execute(); > > > ret = tcg_qemu_tb_exec(env, tb_ptr); > > > cpu->can_do_io = 1; > > > last_tb = (TranslationBlock *)(ret & ~TB_EXIT_MASK); > > > @@ -382,6 +383,7 @@ static inline void tb_add_jump(TranslationBlock *tb, > > > int n, > > > { > > > uintptr_t old; > > > + qemu_thread_jit_write(); > > > assert(n < ARRAY_SIZE(tb->jmp_list_next)); > > > qemu_spin_lock(&tb_next->jmp_lock); > > > diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c > > > index b7d50a73d4..88ae5d35ef 100644 > > > --- a/accel/tcg/translate-all.c > > > +++ b/accel/tcg/translate-all.c > > > @@ -1072,6 +1072,9 @@ static inline void *alloc_code_gen_buffer(void) > > > size_t size = tcg_ctx->code_gen_buffer_size; > > > void *buf; > > > +#if defined(__APPLE__) && defined(MAC_OS_VERSION_11_0) > > > + flags |= MAP_JIT; > > > +#endif > > > buf = mmap(NULL, size, prot, flags, -1, 0); > > > if (buf == MAP_FAILED) { > > > return NULL; > > > @@ -1485,7 +1488,9 @@ static void do_tb_phys_invalidate(TranslationBlock > > > *tb, bool rm_from_page_list) > > > static void tb_phys_invalidate__locked(TranslationBlock *tb) > > > { > > > + qemu_thread_jit_write(); > > > do_tb_phys_invalidate(tb, true); > > > + qemu_thread_jit_execute(); > > > } > > > /* invalidate one TB > > > @@ -1687,6 +1692,7 @@ TranslationBlock *tb_gen_code(CPUState *cpu, > > > #endif > > > assert_memory_lock(); > > > + qemu_thread_jit_write(); > > > phys_pc = get_page_addr_code(env, pc); > > > diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h > > > index f9ec8c84e9..89abebcf5d 100644 > > > --- a/include/qemu/osdep.h > > > +++ b/include/qemu/osdep.h > > > @@ -686,4 +686,7 @@ char *qemu_get_host_name(Error **errp); > > > */ > > > size_t qemu_get_host_physmem(void); > > > +void qemu_thread_jit_write(void); > > > +void qemu_thread_jit_execute(void); > > > + > > > #endif > > > diff --git a/tcg/tcg.c b/tcg/tcg.c > > > index 43c6cf8f52..ab8488f5d5 100644 > > > --- a/tcg/tcg.c > > > +++ b/tcg/tcg.c > > > @@ -1065,6 +1065,7 @@ void tcg_prologue_init(TCGContext *s) > > > s->pool_labels = NULL; > > > #endif > > > + qemu_thread_jit_write(); > > > /* Generate the prologue. */ > > > tcg_target_qemu_prologue(s); > > > diff --git a/util/osdep.c b/util/osdep.c > > > index 66d01b9160..80ec7185da 100644 > > > --- a/util/osdep.c > > > +++ b/util/osdep.c > > > @@ -606,3 +606,25 @@ writev(int fd, const struct iovec *iov, int iov_cnt) > > > return readv_writev(fd, iov, iov_cnt, true); > > > } > > > #endif > > > + > > > +#if defined(__APPLE__) && defined(MAC_OS_VERSION_11_0) > > > Will this be defined in future versions? >
Yes, it will be. But we might explicitly specify upper and lower bounds: https://github.com/phracker/MacOSX-SDKs/blob/master/MacOSX10.15.sdk/usr/include/AvailabilityMacros.h > > > > +static inline void qemu_thread_jit_write_protect(bool enabled) > > > +{ > > > + if (pthread_jit_write_protect_supported_np()) { > > > Do we need this call? Sounds like extra overhead to me. > We don't need it on ARM, but Apple uses it for x86_64 in JavaScriptCore: https://bugs.webkit.org/attachment.cgi?id=402515&action=prettypatch > > > > + pthread_jit_write_protect_np(enabled); > > > + } > > > +} > > > + > > > +void qemu_thread_jit_execute(void) > > > +{ > > > + qemu_thread_jit_write_protect(true); > > > +} > > > + > > > +void qemu_thread_jit_write(void) > > > +{ > > > + qemu_thread_jit_write_protect(false); > > > +} > > What happens if you emulate a -smp 2 ARM guest? In this case MTTCG > > should be enabled (same guest ordering) but you run a risk of attempting > > to execute code while write is enabled. > > > > Is there any way to only change the mapping for the parts of the TB > > cache used by a thread? Otherwise we'll need additional logic in > > default_mttcg_enabled to ensure we don't accidentally enable it on Apple > > silicon. > > > The actual protection logic is per thread, so the MTTCG side thread won't be > affected by the flips. > That's correct. > Given this super specific semantic that is impossible to mimic on other > platforms, we should probably name the functions accordingly and make sure > people understand this is *only* for macos. > I intended to name them accordingly :) I'm sorry if it's not clear. What do you propose instead? > Also, is there anything this patch doesn't do that the one from Joelle does? > It seems a bit ... short. > I tried to minimize amount of W^X fiddling to the bare minimum required for correct operation of TCG. So if you remove any of qemu_thread_jit_*() calls in the patch, TCG won't work. Thanks, Roman
