This patch breaks record/replay. I run execution recording of the WindowsXP machine with the following script:
./bin/qemu-system-i386 -d in_asm,exec -D xp_save.log -global apic-common.vapic=off \ -icount shift=7,rr=record,rrfile=xp0.replay \ -drive file=./images/xp_sp2.qcow2,if=none,id=img-direct,snapshot \ -drive driver=blkreplay,if=none,image=img-direct,id=img-replay \ -device ide-hd,drive=img-replay -net none -m 512M QEMU fails at some moment. Here are the contents of the log: ---------------- IN: 0x806ee2d0: 33 c0 xorl %eax, %eax 0x806ee2d2: 8a c1 movb %cl, %al 0x806ee2d4: 33 c9 xorl %ecx, %ecx 0x806ee2d6: 8a 88 58 e2 6e 80 movb -0x7f911da8(%eax), %cl 0x806ee2dc: 89 0d 80 00 fe ff movl %ecx, 0xfffe0080 0x806ee2e2: a1 80 00 fe ff movl 0xfffe0080, %eax 0x806ee2e7: c3 retl Trace 0: 0x7fdc103b16a0 [00000000/806ee2d0/0x4000b0] qemu: fatal: cpu_io_recompile: could not find TB for pc=0x7fec24fde2de EAX=00000001 EBX=00006901 ECX=0000003d EDX=00000ffc ESI=040d78c0 EDI=0000031f EBP=f878fc60 ESP=f878fc54 EIP=806ee2d0 EFL=00000202 [-------] CPL=0 II=0 A20=1 SMM=0 HLT=0 .... Pavel Dovgalyuk > -----Original Message----- > From: Richard Henderson [mailto:richard.hender...@linaro.org] > Sent: Thursday, June 14, 2018 10:32 PM > To: qemu-devel@nongnu.org > Cc: peter.mayd...@linaro.org; Emilio G. Cota > Subject: [PULL, 14/18] translate-all: discard TB when tb_link_page returns an > existing > matching TB > > From: "Emilio G. Cota" <c...@braap.org> > > Use the recently-gained QHT feature of returning the matching TB if it > already exists. This allows us to get rid of the lookup we perform > right after acquiring tb_lock. > > Suggested-by: Richard Henderson <richard.hender...@linaro.org> > Reviewed-by: Richard Henderson <richard.hender...@linaro.org> > Signed-off-by: Emilio G. Cota <c...@braap.org> > Signed-off-by: Richard Henderson <richard.hender...@linaro.org> > --- > accel/tcg/cpu-exec.c | 14 ++------- > accel/tcg/translate-all.c | 50 +++++++++++++++++++++++++++------ > docs/devel/multi-thread-tcg.txt | 3 ++ > 3 files changed, 46 insertions(+), 21 deletions(-) > > diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c > index d75c35380a..45f6ebc65e 100644 > --- a/accel/tcg/cpu-exec.c > +++ b/accel/tcg/cpu-exec.c > @@ -245,10 +245,7 @@ void cpu_exec_step_atomic(CPUState *cpu) > if (tb == NULL) { > mmap_lock(); > tb_lock(); > - tb = tb_htable_lookup(cpu, pc, cs_base, flags, cf_mask); > - if (likely(tb == NULL)) { > - tb = tb_gen_code(cpu, pc, cs_base, flags, cflags); > - } > + tb = tb_gen_code(cpu, pc, cs_base, flags, cflags); > tb_unlock(); > mmap_unlock(); > } > @@ -398,14 +395,7 @@ static inline TranslationBlock *tb_find(CPUState *cpu, > tb_lock(); > acquired_tb_lock = true; > > - /* There's a chance that our desired tb has been translated while > - * taking the locks so we check again inside the lock. > - */ > - tb = tb_htable_lookup(cpu, pc, cs_base, flags, cf_mask); > - if (likely(tb == NULL)) { > - /* if no translated code available, then translate it now */ > - tb = tb_gen_code(cpu, pc, cs_base, flags, cf_mask); > - } > + tb = tb_gen_code(cpu, pc, cs_base, flags, cf_mask); > > mmap_unlock(); > /* We add the TB in the virtual pc hash table for the fast lookup */ > diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c > index c75298d08a..2585e6fd3e 100644 > --- a/accel/tcg/translate-all.c > +++ b/accel/tcg/translate-all.c > @@ -1581,18 +1581,30 @@ static inline void tb_page_add(PageDesc *p, > TranslationBlock *tb, > * (-1) to indicate that only one page contains the TB. > * > * Called with mmap_lock held for user-mode emulation. > + * > + * Returns a pointer @tb, or a pointer to an existing TB that matches @tb. > + * Note that in !user-mode, another thread might have already added a TB > + * for the same block of guest code that @tb corresponds to. In that case, > + * the caller should discard the original @tb, and use instead the returned > TB. > */ > -static void tb_link_page(TranslationBlock *tb, tb_page_addr_t phys_pc, > - tb_page_addr_t phys_page2) > +static TranslationBlock * > +tb_link_page(TranslationBlock *tb, tb_page_addr_t phys_pc, > + tb_page_addr_t phys_page2) > { > PageDesc *p; > PageDesc *p2 = NULL; > + void *existing_tb = NULL; > uint32_t h; > > assert_memory_lock(); > > /* > * Add the TB to the page list, acquiring first the pages's locks. > + * We keep the locks held until after inserting the TB in the hash table, > + * so that if the insertion fails we know for sure that the TBs are still > + * in the page descriptors. > + * Note that inserting into the hash table first isn't an option, since > + * we can only insert TBs that are fully initialized. > */ > page_lock_pair(&p, phys_pc, &p2, phys_page2, 1); > tb_page_add(p, tb, 0, phys_pc & TARGET_PAGE_MASK); > @@ -1602,21 +1614,33 @@ static void tb_link_page(TranslationBlock *tb, > tb_page_addr_t phys_pc, > tb->page_addr[1] = -1; > } > > + /* add in the hash table */ > + h = tb_hash_func(phys_pc, tb->pc, tb->flags, tb->cflags & CF_HASH_MASK, > + tb->trace_vcpu_dstate); > + qht_insert(&tb_ctx.htable, tb, h, &existing_tb); > + > + /* remove TB from the page(s) if we couldn't insert it */ > + if (unlikely(existing_tb)) { > + tb_page_remove(p, tb); > + invalidate_page_bitmap(p); > + if (p2) { > + tb_page_remove(p2, tb); > + invalidate_page_bitmap(p2); > + } > + tb = existing_tb; > + } > + > if (p2) { > page_unlock(p2); > } > page_unlock(p); > > - /* add in the hash table */ > - h = tb_hash_func(phys_pc, tb->pc, tb->flags, tb->cflags & CF_HASH_MASK, > - tb->trace_vcpu_dstate); > - qht_insert(&tb_ctx.htable, tb, h, NULL); > - > #ifdef CONFIG_USER_ONLY > if (DEBUG_TB_CHECK_GATE) { > tb_page_check(); > } > #endif > + return tb; > } > > /* Called with mmap_lock held for user mode emulation. */ > @@ -1625,7 +1649,7 @@ TranslationBlock *tb_gen_code(CPUState *cpu, > uint32_t flags, int cflags) > { > CPUArchState *env = cpu->env_ptr; > - TranslationBlock *tb; > + TranslationBlock *tb, *existing_tb; > tb_page_addr_t phys_pc, phys_page2; > target_ulong virt_page2; > tcg_insn_unit *gen_code_buf; > @@ -1773,7 +1797,15 @@ TranslationBlock *tb_gen_code(CPUState *cpu, > * memory barrier is required before tb_link_page() makes the TB visible > * through the physical hash table and physical page list. > */ > - tb_link_page(tb, phys_pc, phys_page2); > + existing_tb = tb_link_page(tb, phys_pc, phys_page2); > + /* if the TB already exists, discard what we just translated */ > + if (unlikely(existing_tb != tb)) { > + uintptr_t orig_aligned = (uintptr_t)gen_code_buf; > + > + orig_aligned -= ROUND_UP(sizeof(*tb), qemu_icache_linesize); > + atomic_set(&tcg_ctx->code_gen_ptr, orig_aligned); > + return existing_tb; > + } > tcg_tb_insert(tb); > return tb; > } > diff --git a/docs/devel/multi-thread-tcg.txt b/docs/devel/multi-thread-tcg.txt > index faf8918b23..faf09c6069 100644 > --- a/docs/devel/multi-thread-tcg.txt > +++ b/docs/devel/multi-thread-tcg.txt > @@ -140,6 +140,9 @@ to atomically insert new elements. > The lookup caches are updated atomically and the lookup hash uses QHT > which is designed for concurrent safe lookup. > > +Parallel code generation is supported. QHT is used at insertion time > +as the synchronization point across threads, thereby ensuring that we only > +keep track of a single TranslationBlock for each guest code block. > > Memory maps and TLBs > --------------------