Patchwork [1/2] target-i386: Fix default Hypervisor level for accel=kvm.

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Submitter Don Slutz
Date Sept. 18, 2012, 2:49 p.m.
Message ID <1347979793-27045-2-git-send-email-Don@CloudSwitch.com>
Download mbox | patch
Permalink /patch/184749/
State New
Headers show

Comments

Don Slutz - Sept. 18, 2012, 2:49 p.m.
From http://lkml.indiana.edu/hypermail/linux/kernel/1205.0/00100.html
EAX should be KVM_CPUID_FEATURES (0x40000001) not 0.
---
 target-i386/kvm.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
Eduardo Habkost - Sept. 18, 2012, 3:05 p.m.
On Tue, Sep 18, 2012 at 10:49:52AM -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.
> ---
>  target-i386/kvm.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/target-i386/kvm.c b/target-i386/kvm.c
> index 761a9b1..0c9f5dd 100644
> --- a/target-i386/kvm.c
> +++ b/target-i386/kvm.c
> @@ -392,7 +392,7 @@ int kvm_arch_init_vcpu(CPUX86State *env)
>      c->function = KVM_CPUID_SIGNATURE;
>      if (env->cpuid_hv_level == 0) {
>          memcpy(signature, "KVMKVMKVM\0\0\0", 12);
> -        c->eax = 0;
> +        c->eax = KVM_CPUID_FEATURES;

This makes the CPUID bits to suddenly change, when live-migrating to a
newer QEMU version.

Strictly speaking, this is never supposed to happen, but... on both
cases the meaning of the bits are the same (0 is documented as
equivalent to KVM_CPUID_FEATURES) and probably the guest will look at
them only once on boot. Do we really want to add migration-compatibility
code for this?


>          c->ebx = signature[0];
>          c->ecx = signature[1];
>          c->edx = signature[2];
> -- 
> 1.7.1
>
Don Slutz - Sept. 18, 2012, 8:19 p.m.
On 09/18/12 11:05, Eduardo Habkost wrote:
> On Tue, Sep 18, 2012 at 10:49:52AM -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.
>> ---
>>   target-i386/kvm.c |    2 +-
>>   1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/target-i386/kvm.c b/target-i386/kvm.c
>> index 761a9b1..0c9f5dd 100644
>> --- a/target-i386/kvm.c
>> +++ b/target-i386/kvm.c
>> @@ -392,7 +392,7 @@ int kvm_arch_init_vcpu(CPUX86State *env)
>>       c->function = KVM_CPUID_SIGNATURE;
>>       if (env->cpuid_hv_level == 0) {
>>           memcpy(signature, "KVMKVMKVM\0\0\0", 12);
>> -        c->eax = 0;
>> +        c->eax = KVM_CPUID_FEATURES;
> This makes the CPUID bits to suddenly change, when live-migrating to a
> newer QEMU version.
>
> Strictly speaking, this is never supposed to happen, but... on both
> cases the meaning of the bits are the same (0 is documented as
> equivalent to KVM_CPUID_FEATURES) and probably the guest will look at
> them only once on boot. Do we really want to add migration-compatibility
> code for this?
>
My vote would be no; because this should be ok and the tests that I know 
of are all at boot time.  I will look into adding 
migration-compatibility.  I also do not have any direct need for this 
change, it just looked like the right thing to do.
>>           c->ebx = signature[0];
>>           c->ecx = signature[1];
>>           c->edx = signature[2];
>> -- 
>> 1.7.1
>>

Patch

diff --git a/target-i386/kvm.c b/target-i386/kvm.c
index 761a9b1..0c9f5dd 100644
--- a/target-i386/kvm.c
+++ b/target-i386/kvm.c
@@ -392,7 +392,7 @@  int kvm_arch_init_vcpu(CPUX86State *env)
     c->function = KVM_CPUID_SIGNATURE;
     if (env->cpuid_hv_level == 0) {
         memcpy(signature, "KVMKVMKVM\0\0\0", 12);
-        c->eax = 0;
+        c->eax = KVM_CPUID_FEATURES;
         c->ebx = signature[0];
         c->ecx = signature[1];
         c->edx = signature[2];