Date: Wed, 11 Nov 2026 13:48:48 +0200
From: Doru =?iso-8859-1?Q?Bl=E2nzeanu?= <dblanzeanu@linux.microsoft.com>
To: Magnus Kulke <magnuskulke@linux.microsoft.com>
Cc: qemu-devel@nongnu.org, Magnus Kulke <magnuskulke@microsoft.com>,
 Wei Liu <wei.liu@kernel.org>,
 Doru =?iso-8859-1?Q?Bl=E2nzeanu?= <doru.blanzeanu@microsoft.com>
Subject: Re: [PATCH] target/i386/mshv: fix vCPU run result contract
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References: <20261015121911.279817-1-magnuskulke@linux.microsoft.com>
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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>