Re: [PATCH v2] target/i386: Give IRQs a chance when resetting HF_INHIBIT_IRQ_MASK

[Philippe Mathieu-Daudé]

On 15/4/24 11:32, Paolo Bonzini wrote:

On Mon, Apr 15, 2024 at 8:50 AM Ruihan Li <lrh2...@pku.edu.cn> 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.

Thanks, interesting bug!

What do you think about writing this:

      /* 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;
      }

in a slightly simpler manner:

     inhibit_reset = false;
     if (s->flags & HF_INHIBIT_IRQ_MASK) {
         gen_reset_hflag(s, HF_INHIBIT_IRQ_MASK);
         inhibit_reset = true;
     } else if (inhibit) {
         gen_set_hflag(s, HF_INHIBIT_IRQ_MASK);
     }

No need to submit v3, I can do the change myself when applying.

Cc: qemu-sta...@nongnu.org