Re: [PATCH] target/i386: raise FERR interrupt with iothread locked

[Peter Maydell]

On Tue, 29 Aug 2023 at 17:59, Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> On Tue, Aug 29, 2023 at 5:46 PM Philippe Mathieu-Daudé
> <philmd@linaro.org> wrote:
> >
> > On 29/8/23 17:25, Paolo Bonzini wrote:
> > > Otherwise tcg_handle_interrupt() triggers an assertion failure:
> > >
> > >    #5  0x0000555555c97369 in tcg_handle_interrupt (cpu=0x555557434cb0, 
> > > mask=2) at ../accel/tcg/tcg-accel-ops.c:83
> > >    #6  tcg_handle_interrupt (cpu=0x555557434cb0, mask=2) at 
> > > ../accel/tcg/tcg-accel-ops.c:81
> > >    #7  0x0000555555b4d58b in pic_irq_request (opaque=<optimized out>, 
> > > irq=<optimized out>, level=1) at ../hw/i386/x86.c:555
> > >    #8  0x0000555555b4f218 in gsi_handler (opaque=0x5555579423d0, n=13, 
> > > level=1) at ../hw/i386/x86.c:611
> > >    #9  0x00007fffa42bde14 in code_gen_buffer ()
> > >    #10 0x0000555555c724bb in cpu_tb_exec (cpu=cpu@entry=0x555557434cb0, 
> > > itb=<optimized out>, tb_exit=tb_exit@entry=0x7fffe9bfd658) at 
> > > ../accel/tcg/cpu-exec.c:457
> > >
> > > Cc: qemu-stable@nongnu.org
> > > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1808
> > > Reported-by: NyanCatTW1 <https://gitlab.com/a0939712328>
> > > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> > > ---
> > >   target/i386/tcg/sysemu/fpu_helper.c | 2 ++
> > >   1 file changed, 2 insertions(+)
> > >
> > > diff --git a/target/i386/tcg/sysemu/fpu_helper.c 
> > > b/target/i386/tcg/sysemu/fpu_helper.c
> > > index 1c3610da3b9..fd8cc72a026 100644
> > > --- a/target/i386/tcg/sysemu/fpu_helper.c
> > > +++ b/target/i386/tcg/sysemu/fpu_helper.c
> > > @@ -31,7 +31,9 @@ void x86_register_ferr_irq(qemu_irq irq)
> > >   void fpu_check_raise_ferr_irq(CPUX86State *env)
> > >   {
> > >       if (ferr_irq && !(env->hflags2 & HF2_IGNNE_MASK)) {
> > > +        qemu_mutex_lock_iothread();
> > >           qemu_irq_raise(ferr_irq);
> > > +        qemu_mutex_unlock_iothread();
> > >           return;
> > >       }
> > >   }
> >
> > OK, so:
> >
> > Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
>
> Actually Richard has a better (though also slightly incomplete) patch
> in the bug, so I'll send v2.
>
> >   void cpu_set_ignne(void)
> >   {
> >       CPUX86State *env = &X86_CPU(first_cpu)->env;
> > +
> > +    g_assert(qemu_mutex_iothread_locked());
>
> qemu_irq_lower() is fine because it doesn't result in a call to
> tcg_handle_interrupt().

It does potentially result in calling code in a device model
that assumes that it is protected by the iothread lock,
though...

-- PMM