Re: [PATCH] target/i386/mshv: fix vCPU run result contract

[Magnus Kulke <magnuskulke@linux.microsoft.com>]

On Wed, Nov 11, 2026 at 01:48:48PM +0200, Doru Blânzeanu wrote:
> On Thu, Oct 15, 2026 at 02:19:11PM +0200, Magnus Kulke wrote:
> > Currently the return semantics of mshv_run_vcpu() are broken. They
> > return a mix of int and exit_reason, ignoring the out param *exit.
> > 
> > This change propagates errno's to the call site and sets the *exit value
> > accordingly. We also consider the case when an ioctl has return due to a
> > qemu-requested interruption of the call, this is a legitimate condition
> > that should not produce an error.
> > 
> > Fixes: 6dec60528c4 (target/i386/mshv: Implement mshv_vcpu_run())
> > Signed-off-by: Magnus Kulke <magnuskulke@linux.microsoft.com>
> > ---
> >  target/i386/mshv/mshv-cpu.c | 28 +++++++++++++++++-----------
> >  1 file changed, 17 insertions(+), 11 deletions(-)
> > 
> > diff --git a/target/i386/mshv/mshv-cpu.c b/target/i386/mshv/mshv-cpu.c
> > index 4df73bb497..e3c155da2e 100644
> > --- a/target/i386/mshv/mshv-cpu.c
> > +++ b/target/i386/mshv/mshv-cpu.c
> > @@ -2124,7 +2124,6 @@ static int arch_set_single_step(CPUState *cpu, bool enable)
> >  int mshv_run_vcpu(int vm_fd, CPUState *cpu, hv_message *msg, MshvVmExit *exit)
> >  {
> >      int ret;
> > -    enum MshvVmExit exit_reason;
> >      int cpu_fd = mshv_vcpufd(cpu);
> >      bool single_step;
> >  
> > @@ -2142,7 +2141,12 @@ int mshv_run_vcpu(int vm_fd, CPUState *cpu, hv_message *msg, MshvVmExit *exit)
> >  
> >      ret = ioctl(cpu_fd, MSHV_RUN_VP, msg);
> >      if (ret < 0) {
> > -        return MshvVmExitShutdown;
> > +        if (errno == EINTR) {
> > +            *exit = MshvVmExitSpecial;
> > +            return 0;
> > +        }
> > +        error_report("failed to run vCPU: %s", strerror(errno));
> > +        return -errno;
> >      }
> >  
> >      /* disable single stepping by flipping RFLAGS.TF */
> > @@ -2154,31 +2158,33 @@ int mshv_run_vcpu(int vm_fd, CPUState *cpu, hv_message *msg, MshvVmExit *exit)
> >  
> >      switch (msg->header.message_type) {
> >      case HVMSG_UNRECOVERABLE_EXCEPTION:
> > -        return MshvVmExitShutdown;
> > +        *exit = MshvVmExitShutdown;
> > +        return 0;
> >      case HVMSG_UNMAPPED_GPA:
> >      case HVMSG_GPA_INTERCEPT:
> > -        ret = handle_mmio(cpu, msg, &exit_reason);
> > +        ret = handle_mmio(cpu, msg, exit);
> >          if (ret < 0) {
> >              error_report("failed to handle mmio");
> > -            return -1;
> > +            return ret;
> >          }
> > -        return exit_reason;
> > +        return 0;
> >      case HVMSG_X64_IO_PORT_INTERCEPT:
> >          ret = handle_pio(cpu, msg);
> >          if (ret < 0) {
> > -            return MshvVmExitSpecial;
> > +            error_report("failed to handle PIO");
> > +            return ret;
> >          }
> > -        return MshvVmExitIgnore;
> > +        *exit = MshvVmExitIgnore;
> > +        return 0;
> >      case HVMSG_X64_EXCEPTION_INTERCEPT:
> >          bql_lock();
> > -        ret = handle_exception_interrupt(cpu, msg, &exit_reason);
> > +        ret = handle_exception_interrupt(cpu, msg, exit);
> >          bql_unlock();
> >          if (ret < 0) {
> >              error_report("failed to handle exception intercept");
> >              return -1;
> >          }
> > -        *exit = exit_reason;
> > -        return exit_reason;
> > +        return 0;
> >      default:
> >          break;
> >      }
> > -- 
> > 2.34.1
> 
> Reviewed-by: Doru Blânzeanu <dblanzeanu@linux.microsoft.com>

queued in pull-20261111