Re: [Qemu-devel] [PATCH] x86: Fix Opteron xlevels

[Alexander Graf <agraf@suse.de>]

On 04/22/2015 04:23 PM, Eduardo Habkost wrote:
> On Tue, Apr 21, 2015 at 04:15:14PM +0200, Alexander Graf wrote:
>> On 04/21/2015 04:16 PM, Eduardo Habkost wrote:
>>> On Tue, Apr 21, 2015 at 04:04:21PM +0200, Alexander Graf wrote:
>>>> The AMD Opteron family has different xlevel levels depending on the
>>>> generation. I looked up Gen1, Gen2 and Gen3 hardware and adapted the
>>>> levels according to real silicon.
>>>>
>>>> The reason this came up is that there is a sanity check in KVM making
>>>> sure that SVM is only used when xlevel is high enough. Using real
>>>> hardware levels, they now are.
>>>>
>>>> Reported-by: Bernhard M. Wiedemann <bwiedemann@suse.de>
>>>> Signed-off-by: Alexander Graf <agraf@suse.de>
>>> It needs compatibility properties in HW_COMPAT_2_1.  See commit
>>> 6b11322e0f724eb0649fdc324a44288b783023ad for reference.
>> Ah, sure, will do.
>>
>>>> ---
>>>>   target-i386/cpu.c | 6 +++---
>>>>   1 file changed, 3 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/target-i386/cpu.c b/target-i386/cpu.c
>>>> index 03b33cf..d1b1b8c 100644
>>>> --- a/target-i386/cpu.c
>>>> +++ b/target-i386/cpu.c
>>>> @@ -1234,7 +1234,7 @@ static X86CPUDefinition builtin_x86_defs[] = {
>>>>               CPUID_EXT2_MTRR | CPUID_EXT2_SYSCALL | CPUID_EXT2_APIC |
>>>>               CPUID_EXT2_CX8 | CPUID_EXT2_MCE | CPUID_EXT2_PAE | CPUID_EXT2_MSR |
>>>>               CPUID_EXT2_TSC | CPUID_EXT2_PSE | CPUID_EXT2_DE | CPUID_EXT2_FPU,
>>>> -        .xlevel = 0x80000008,
>>>> +        .xlevel = 0x80000018,
>>> Why did you choose 0x80000018? The highest 0x80000000 leaf we implement
>>> today is 0x8000000A. SVM info is at 0x8000000A.
>> Because it's what real hardware exposes ;).
> Real hardware exposes 0x80000018 because it does return useful
> information in some of the 0x8000000B-0x80000018 leaves.
>
> We don't return anything useful in CPUID leaves above 0x8000000a[1], so
> what exactly are you trying to do by reporting leaves
> 0x8000000B-0x80000018 as available?

Considering that the G4 Opteron exposes 0x1a I'd say we have that 
problem already. So if we want to fix the unpopulated leafs, we need to 
do that regardless.


Alex

>
> [1] I don't even know what's present in those leaves. I will check the
>      Intel and AMD docs right now.
>