Re: [Qemu-devel] [PATCH 2/2] target-i386: Fix default Hypervisor level for hypervisor-vendor=kvm.

[Don Slutz <Don@CloudSwitch.Com>]

On 09/18/12 13:00, Eduardo Habkost wrote:
> On Tue, Sep 18, 2012 at 10:49:53AM -0400, Don Slutz wrote:
>>  From http://lkml.indiana.edu/hypermail/linux/kernel/1205.0/00100.html
>> EAX should be KVM_CPUID_FEATURES (0x40000001) not 0.
>>
>> If kvm is not configured, the additional option of hypervisor-level=1
>> (or hypervisor-level=0x40000001) needs to be specified to get this.
>> ---
>>   target-i386/cpu.c |   12 +++++++++++-
>>   1 files changed, 11 insertions(+), 1 deletions(-)
>>
>> diff --git a/target-i386/cpu.c b/target-i386/cpu.c
>> index 6e43eff..d73b0a8 100644
>> --- a/target-i386/cpu.c
>> +++ b/target-i386/cpu.c
>> @@ -1248,7 +1248,12 @@ static char *x86_cpuid_get_hv_vendor(Object *obj, Error **errp)
>>                  env->cpuid_hv_level == CPUID_HV_LEVEL_XEN) {
>>           pstrcpy(value, sizeof(value), "xen");
>>       } else if (!strcmp(value, CPUID_HV_VENDOR_KVM) &&
>> -               env->cpuid_hv_level == 0) {
>> +#if defined(CONFIG_KVM)
>> +               env->cpuid_hv_level == KVM_CPUID_FEATURES
>> +#else
>> +               env->cpuid_hv_level == 0
>> +#endif
>> +	    ) {
>>           pstrcpy(value, sizeof(value), "kvm");
>>       }
>>       return value;
>> @@ -1281,6 +1286,11 @@ static void x86_cpuid_set_hv_vendor(Object *obj, const char *value,
>>           }
>>           pstrcpy(adj_value, sizeof(adj_value), CPUID_HV_VENDOR_XEN);
>>       } else if (!strcmp(value, "kvm")) {
>> +#if defined(CONFIG_KVM)
>> +        if (env->cpuid_hv_level == 0) {
>> +            env->cpuid_hv_level = KVM_CPUID_FEATURES;
>> +        }
>> +#endif
> If CPUID[0x40000000].EAX set to 0 is documented as equivalent to having
> it set to 0x40000001 (KVM_CPUID_FEATURES), why the confusing checks for
> CONFIG_KVM? Why not always set it to KVM_CPUID_FEATURES?
>
At line 36 of the file:

#if defined(CONFIG_KVM)
#include <linux/kvm_para.h>
#endif

So without the check you get compile failures (i386-linux-user).

I have no issue with removing the check(s) for 0.  Currently 
hypervisor-level=0 will not force the old values; I can make a change so 
that works.
      -Don Slutz