Hi all, On Mon, Dec 11, 2023 at 03:01:48AM +0800, Ruihan Li wrote: > When emulated with QEMU, interrupts will never come in the following > loop. However, if the NOP instruction is uncommented, interrupts will > fire as normal. > > loop: > cli > call do_sti > jmp loop > > do_sti: > sti > # nop > ret > > This behavior is different from that of a real processor. For example, > if KVM is enabled, interrupts will always fire regardless of whether the > NOP instruction is commented or not. Also, the Intel Software Developer > Manual states that after the STI instruction is executed, the interrupt > inhibit should end as soon as the next instruction (e.g., the RET > instruction if the NOP instruction is commented) is executed. > > This problem is caused because the previous code may choose not to end > the TB even if the HF_INHIBIT_IRQ_MASK has just been reset (e.g., in the > case where the RET instruction is immediately followed by the STI > instruction), so that IRQs may not have a change to trigger. This commit > fixes the problem by always terminating the current TB to give IRQs a > chance to trigger when HF_INHIBIT_IRQ_MASK is reset. > > Signed-off-by: Ruihan Li <lrh2...@pku.edu.cn> > --- > The same problem was discovered two years ago, see [StackOverflow][so]. > > [so]: > https://stackoverflow.com/questions/68135305/executing-ret-after-sti-doesnt-start-interrupts > > target/i386/tcg/translate.c | 12 ++++++++++-- > 1 file changed, 10 insertions(+), 2 deletions(-) > > diff --git a/target/i386/tcg/translate.c b/target/i386/tcg/translate.c > index 587d886..6b7deb5 100644 > --- a/target/i386/tcg/translate.c > +++ b/target/i386/tcg/translate.c > @@ -2767,13 +2767,19 @@ static void gen_bnd_jmp(DisasContext *s) > static void > do_gen_eob_worker(DisasContext *s, bool inhibit, bool recheck_tf, bool jr) > { > + bool inhibit_reset; > + > gen_update_cc_op(s); > > /* If several instructions disable interrupts, only the first does it. > */ > if (inhibit && !(s->flags & HF_INHIBIT_IRQ_MASK)) { > gen_set_hflag(s, HF_INHIBIT_IRQ_MASK); > - } else { > + inhibit_reset = false; > + } else if (!inhibit && (s->flags & HF_INHIBIT_IRQ_MASK)) { > gen_reset_hflag(s, HF_INHIBIT_IRQ_MASK); > + inhibit_reset = true; > + } else { > + inhibit_reset = false; > } > > if (s->base.tb->flags & HF_RF_MASK) { > @@ -2784,7 +2790,9 @@ do_gen_eob_worker(DisasContext *s, bool inhibit, bool > recheck_tf, bool jr) > tcg_gen_exit_tb(NULL, 0); > } else if (s->flags & HF_TF_MASK) { > gen_helper_single_step(tcg_env); > - } else if (jr) { > + } else if (jr && > + /* give irqs a chance to happen */ > + !inhibit_reset) { > tcg_gen_lookup_and_goto_ptr(); > } else { > tcg_gen_exit_tb(NULL, 0); > -- > 2.43.0
A friendly ping. Anyone here to confirm this BUG and/or comment on the patch? Thanks, Ruihan Li
