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

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

[Mohammed Gamal]

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;
+}
 
 static inline void set_gsi(kvm_context_t kvm, unsigned int gsi)
 {
@@ -586,7 +600,7 @@ int kvm_run(CPUState *env)
             r = handle_unhandled(run->hw.hardware_exit_reason);
             break;
         case KVM_EXIT_FAIL_ENTRY:
-            r = handle_unhandled(run->fail_entry.hardware_entry_failure_reason);
+            r = handle_failed_vmentry(run->fail_entry.hardware_entry_failure_reason);
             break;
         case KVM_EXIT_EXCEPTION:
             fprintf(stderr, "exception %d (%x)\n", run->ex.exception,
-- 
1.7.0.4

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

[Anthony Liguori]

On 05/19/2010 04:16 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;
> +}
>
>    

Very nice.

Regards,

Anthony Liguori

>   static inline void set_gsi(kvm_context_t kvm, unsigned int gsi)
>   {
> @@ -586,7 +600,7 @@ int kvm_run(CPUState *env)
>               r = handle_unhandled(run->hw.hardware_exit_reason);
>               break;
>           case KVM_EXIT_FAIL_ENTRY:
> -            r = handle_unhandled(run->fail_entry.hardware_entry_failure_reason);
> +            r = handle_failed_vmentry(run->fail_entry.hardware_entry_failure_reason);
>               break;
>           case KVM_EXIT_EXCEPTION:
>               fprintf(stderr, "exception %d (%x)\n", run->ex.exception,
>    

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

[Ryan Harper]

* Mohammed Gamal <m.gamal005@gmail.com> [2010-05-19 16:17]:
> 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");

We might want to qualify this with certain cpu versions.  IIRC, the VMX
unrestricted mode should handle big real mode correctly, no?   Maybe, 

+    fprintf(stderr, "on some Intel processors. For example, the guest maybe running in big\n");
+    fprintf(stderr, "real mode which is not supported on most Intel processors.\n\n");

-- 
Ryan Harper
Software Engineer; Linux Technology Center
IBM Corp., Austin, Tx
ryanh@us.ibm.com

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

[Mohammed Gamal]

On Thu, May 20, 2010 at 4:28 AM, Ryan Harper <ryanh@us.ibm.com> wrote:
>
> * Mohammed Gamal <m.gamal005@gmail.com> [2010-05-19 16:17]:
> > 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");
>
> We might want to qualify this with certain cpu versions.  IIRC, the VMX
> unrestricted mode should handle big real mode correctly, no?   Maybe,
>
> +    fprintf(stderr, "on some Intel processors. For example, the guest maybe running in big\n");
> +    fprintf(stderr, "real mode which is not supported on most Intel processors.\n\n");
>
Good point. Will correct and resend.

> --
> Ryan Harper
> Software Engineer; Linux Technology Center
> IBM Corp., Austin, Tx
> ryanh@us.ibm.com

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

[Mohammed Gamal]

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 |   19 ++++++++++++++++++-
 1 files changed, 18 insertions(+), 1 deletions(-)

diff --git a/qemu-kvm.c b/qemu-kvm.c
index 35a4c8a..1fdb6fe 100644
--- a/qemu-kvm.c
+++ b/qemu-kvm.c
@@ -106,6 +106,23 @@ 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 without\n");
+    fprintf(stderr, "unrestricted mode support, the failure can be most likely\n");
+    fprintf(stderr, "due to the guest entering an invalid state for Intel VT.\n");
+    fprintf(stderr, "For example, the guest maybe running in big real mode\n");
+    fprintf(stderr, "which is not supported on less recent Intel processors.\n\n");
+    fprintf(stderr, "You may want to try enabling KVM real mode emulation. To\n");
+    fprintf(stderr, "enable it, you can 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\n");
+    fprintf(stderr, "WARNING: Real mode emulation is still work-in-progress\n");
+    fprintf(stderr, "and thus it is not always guaranteed to work.\n\n");
+    return -EINVAL;
+}
 
 static inline void set_gsi(kvm_context_t kvm, unsigned int gsi)
 {
@@ -586,7 +603,7 @@ int kvm_run(CPUState *env)
             r = handle_unhandled(run->hw.hardware_exit_reason);
             break;
         case KVM_EXIT_FAIL_ENTRY:
-            r = handle_unhandled(run->fail_entry.hardware_entry_failure_reason);
+            r = handle_failed_vmentry(run->fail_entry.hardware_entry_failure_reason);
             break;
         case KVM_EXIT_EXCEPTION:
             fprintf(stderr, "exception %d (%x)\n", run->ex.exception,
-- 
1.7.0.4

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

[Chris Lalancette]

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

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

[Anthony Liguori]

On 05/20/2010 09:37 AM, Chris Lalancette wrote:
> 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.
>    

We should probably only display this message if reason == 0x80000021.  
It may be worth looking at the cpu_state to verify that we're trying to 
enter 16-bit mode too.

Then the message can be much more definitive too.

Regards,

Anthony Liguori

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

[Mohammed Gamal]

On Thu, May 20, 2010 at 5:37 PM, Chris Lalancette <clalance@redhat.com> wrote:
> 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.
>
Your point is definitely valid, yet big real mode is usually the most
likely case, and that's why this message is shown. Note also that it
says it's _most likely_ a failure caused by an invalid guest state,
but it doesn't rule out all other reasons. And in any case, it'd be
better than just printing something along the lines of:
" kvm: unhandled exit 80000021
  kvm_run returned -22"

> --
> Chris Lalancette
>

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

[Avi Kivity]

On 05/20/2010 05:46 PM, Mohammed Gamal wrote:
> On Thu, May 20, 2010 at 5:37 PM, Chris Lalancette<clalance@redhat.com>  wrote:
>    
>> 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.
>>
>>      
> Your point is definitely valid, yet big real mode is usually the most
> likely case, and that's why this message is shown. Note also that it
> says it's _most likely_ a failure caused by an invalid guest state,
> but it doesn't rule out all other reasons. And in any case, it'd be
> better than just printing something along the lines of:
> " kvm: unhandled exit 80000021
>    kvm_run returned -22"
>    

However, we're still giving bad advice.  Currently 
emulate_invalid_guest_state=1 is not going to work well (right?).  Once 
it does, we'll simply make it the default and the message will never appear.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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

[Mohammed Gamal]

On Thu, May 20, 2010 at 6:53 PM, Avi Kivity <avi@redhat.com> wrote:
> On 05/20/2010 05:46 PM, Mohammed Gamal wrote:
>>
>> On Thu, May 20, 2010 at 5:37 PM, Chris Lalancette<clalance@redhat.com>
>>  wrote:
>>
>>>
>>> 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.
>>>
>>>
>>
>> Your point is definitely valid, yet big real mode is usually the most
>> likely case, and that's why this message is shown. Note also that it
>> says it's _most likely_ a failure caused by an invalid guest state,
>> but it doesn't rule out all other reasons. And in any case, it'd be
>> better than just printing something along the lines of:
>> " kvm: unhandled exit 80000021
>>   kvm_run returned -22"
>>
>
> However, we're still giving bad advice.  Currently
> emulate_invalid_guest_state=1 is not going to work well (right?).  Once it
> does, we'll simply make it the default and the message will never appear.
>
I already added a warning in the second patch I sent.

> --
> Do not meddle in the internals of kernels, for they are subtle and quick to
> panic.
>
>

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

[Mohammed Gamal]

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 |   27 ++++++++++++++++++++++++++-
 1 files changed, 26 insertions(+), 1 deletions(-)

diff --git a/qemu-kvm.c b/qemu-kvm.c
index 35a4c8a..3ef0565 100644
--- a/qemu-kvm.c
+++ b/qemu-kvm.c
@@ -106,6 +106,31 @@ static int handle_unhandled(uint64_t reason)
     return -EINVAL;
 }
 
+#define VMX_INVALID_GUEST_STATE 0x21
+
+static int handle_failed_vmentry(uint64_t reason)
+{
+    fprintf(stderr, "kvm: vm entry failed with error 0x%" PRIx64 "\n\n", reason);
+
+    /* Perhaps we will need to check if this machine is intel since exit reason 0x21 
+       has a different interpretation on SVM */
+    if (reason == VMX_INVALID_GUEST_STATE) {
+        fprintf(stderr, "If you're runnning a guest on an Intel machine without\n");
+        fprintf(stderr, "unrestricted mode support, the failure can be most likely\n");
+        fprintf(stderr, "due to the guest entering an invalid state for Intel VT.\n");
+        fprintf(stderr, "For example, the guest maybe running in big real mode\n");
+        fprintf(stderr, "which is not supported on less recent Intel processors.\n\n");
+        fprintf(stderr, "You may want to try enabling KVM real mode emulation. To\n");
+        fprintf(stderr, "enable it, you can 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\n");
+        fprintf(stderr, "WARNING: Real mode emulation is still work-in-progress\n");
+        fprintf(stderr, "and thus it is not always guaranteed to work.\n\n");
+    }
+
+    return -EINVAL;
+}
 
 static inline void set_gsi(kvm_context_t kvm, unsigned int gsi)
 {
@@ -586,7 +611,7 @@ int kvm_run(CPUState *env)
             r = handle_unhandled(run->hw.hardware_exit_reason);
             break;
         case KVM_EXIT_FAIL_ENTRY:
-            r = handle_unhandled(run->fail_entry.hardware_entry_failure_reason);
+            r = handle_failed_vmentry(run->fail_entry.hardware_entry_failure_reason);
             break;
         case KVM_EXIT_EXCEPTION:
             fprintf(stderr, "exception %d (%x)\n", run->ex.exception,
-- 
1.7.0.4

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

[Mohammed Gamal]

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 |   20 +++++++++++++++++++-
 1 files changed, 19 insertions(+), 1 deletions(-)

diff --git a/qemu-kvm.c b/qemu-kvm.c
index 9534b31..1a66f55 100644
--- a/qemu-kvm.c
+++ b/qemu-kvm.c
@@ -106,6 +106,24 @@ static int handle_unhandled(uint64_t reason)
     return -EINVAL;
 }
 
+#define VMX_INVALID_GUEST_STATE 0x80000021
+
+static int handle_failed_vmentry(uint64_t reason)
+{
+    fprintf(stderr, "kvm: vm entry failed with error 0x%" PRIx64 "\n\n", reason);
+
+    /* Perhaps we will need to check if this machine is intel since exit reason 0x21 
+       has a different interpretation on SVM */
+    if (reason == VMX_INVALID_GUEST_STATE) {
+        fprintf(stderr, "If you're runnning a guest on an Intel machine without\n");
+        fprintf(stderr, "unrestricted mode support, the failure can be most likely\n");
+        fprintf(stderr, "due to the guest entering an invalid state for Intel VT.\n");
+        fprintf(stderr, "For example, the guest maybe running in big real mode\n");
+        fprintf(stderr, "which is not supported on less recent Intel processors.\n\n");
+    }
+
+    return -EINVAL;
+}
 
 static inline void set_gsi(kvm_context_t kvm, unsigned int gsi)
 {
@@ -586,7 +604,7 @@ int kvm_run(CPUState *env)
             r = handle_unhandled(run->hw.hardware_exit_reason);
             break;
         case KVM_EXIT_FAIL_ENTRY:
-            r = handle_unhandled(run->fail_entry.hardware_entry_failure_reason);
+            r = handle_failed_vmentry(run->fail_entry.hardware_entry_failure_reason);
             break;
         case KVM_EXIT_EXCEPTION:
             fprintf(stderr, "exception %d (%x)\n", run->ex.exception,
-- 
1.7.0.4

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

[Avi Kivity]

On 06/06/2010 02:10 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.
>
>    

Applied, thanks.

-- 
error compiling committee.c: too many arguments to function