Re: [PATCH] Print a user-friendly message on failed vmentry

[Chris Lalancette <clalance@redhat.com>]

On 05/19/2010 05:16 PM, Mohammed Gamal wrote:
> This patch address bug report in https://bugs.launchpad.net/qemu/+bug/530077.
> 
> Failed vmentries were handled with handle_unhandled() which prints a rather
> unfriendly message to the user. This patch separates handling vmentry failures
> from unknown exit reasons and prints a friendly message to the user.
> 
> Signed-off-by: Mohammed Gamal <m.gamal005@gmail.com>
> ---
>  qemu-kvm.c |   16 +++++++++++++++-
>  1 files changed, 15 insertions(+), 1 deletions(-)
> 
> diff --git a/qemu-kvm.c b/qemu-kvm.c
> index 35a4c8a..deb4df8 100644
> --- a/qemu-kvm.c
> +++ b/qemu-kvm.c
> @@ -106,6 +106,20 @@ static int handle_unhandled(uint64_t reason)
>      return -EINVAL;
>  }
>  
> +static int handle_failed_vmentry(uint64_t reason)
> +{
> +    fprintf(stderr, "kvm: vm entry failed with error 0x%" PRIx64 "\n\n", reason);
> +    fprintf(stderr, "If you're runnning a guest on an Intel machine, it can be\n");
> +    fprintf(stderr, "most-likely due to the guest going into an invalid state\n");
> +    fprintf(stderr, "for Intel VT. For example, the guest maybe running in big\n");
> +    fprintf(stderr, "real mode which is not supported by Intel VT.\n\n");
> +    fprintf(stderr, "You may want to try enabling real mode emulation in KVM.\n");
> +    fprintf(stderr, "To Enable it, you may run the following commands as root:\n");
> +    fprintf(stderr, "# rmmod kvm_intel\n");
> +    fprintf(stderr, "# rmmod kvm\n");
> +    fprintf(stderr, "# modprobe kvm_intel emulate_invalid_guest_state=1\n");
> +    return -EINVAL;
> +}

The thing is, there are other valid reasons for vmentry failure.  A while ago I tracked
down a bug in the Linux kernel that was causing us to vmenter with invalid segments;
this message would have been very misleading in that case.  I think you'd have to do
more complete analysis of the vmentry failure code to be more certain about the reason
for failure.

-- 
Chris Lalancette