Il 08/09/2013 13:40, Gleb Natapov ha scritto:
> On Thu, Sep 05, 2013 at 03:06:21PM +0200, Paolo Bonzini wrote:
>> On KVM, the KVM_SET_XSAVE would be executed with a 0 xstate_bv,
>> and not restore anything.
>>
> XRSTOR restores FP/SSE state to reset state if no bits are set in
> xstate_bv. This is what should happen on reset, no?
Yes. The problem happens on the migration destination when XSAVE data is
not transmitted. FP/SSE data is transmitted and must be restored, but
xstate_bv is zero and KVM_SET_XSAVE restores FP/SSE state to reset
state. The vcpu then loses the values that were set in the migration data.
>> Since FP and SSE data are always valid, set them in xstate_bv at reset
>> time. In fact, that value is the same that KVM_GET_XSAVE returns on
>> pre-XSAVE hosts.
> It is needed for migration between non xsave host to xsave host.
Yes, and this patch does the same for migration between non-XSAVE QEMU
and XSAVE QEMU.
In fact, another bug is that kvm_vcpu_ioctl_x86_set_xsave ignores
xstate_bv when XSAVE is not available. Instead, it should reset the
FXSAVE data to processor-reset values (except for MXCSR which always
comes from XRSTOR data), i.e. to all-zeros except for the x87 control
and tag words. It should also check reserved bits of MXCSR.
>>
>> Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
>> ---
>> target-i386/cpu.c | 1 +
>> target-i386/cpu.h | 5 +++++
>> 2 files changed, 6 insertions(+)
>>
>> diff --git a/target-i386/cpu.c b/target-i386/cpu.c
>> index c36345e..ac83106 100644
>> --- a/target-i386/cpu.c
>> +++ b/target-i386/cpu.c
>> @@ -2386,6 +2386,7 @@ static void x86_cpu_reset(CPUState *s)
>> env->fpuc = 0x37f;
>>
>> env->mxcsr = 0x1f80;
>> + env->xstate_bv = XSTATE_FP | XSTATE_SSE;
>>
>> env->pat = 0x0007040600070406ULL;
>> env->msr_ia32_misc_enable = MSR_IA32_MISC_ENABLE_DEFAULT;
>> diff --git a/target-i386/cpu.h b/target-i386/cpu.h
>> index 5723eff..a153078 100644
>> --- a/target-i386/cpu.h
>> +++ b/target-i386/cpu.h
>> @@ -380,6 +380,11 @@
>>
>> #define MSR_VM_HSAVE_PA 0xc0010117
>>
>> +#define XSTATE_SUPPORTED (XSTATE_FP|XSTATE_SSE|XSTATE_YMM)
> Supported by whom? By QEMU? We should filer unsupported bits from CPUID.0D
> then too.
Yes. QEMU unmarshals information from the XSAVE region and back, so it
cannot support MPX or AVX-512 yet (even if KVM were). Separate bug, though.
Paolo
>
>> +#define XSTATE_FP 1
>> +#define XSTATE_SSE 2
>> +#define XSTATE_YMM 4
>> +
>> /* CPUID feature words */
>> typedef enum FeatureWord {
>> FEAT_1_EDX, /* CPUID[1].EDX */
>> --
>> 1.8.3.1
>>
>
> --
> Gleb.
> --
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