2015-11-19 19:05 GMT+08:00 Paolo Bonzini <pbonzini@xxxxxxxxxx>:
>
>
> On 19/11/2015 11:45, Wanpeng li wrote:
>> Intel cpu doesn't support syscall/sysret in non 64-bit mode which
>> is different from AMD. Expose syscall/sysret to intel 32-bit guest
>> just makes no sense and leads to #UD which will confuse the users.
>>
>> This patch disable expose syscall/sysret to intel 32-bit guest.
>>
>> Signed-off-by: Wanpeng li <wanpeng.li@xxxxxxxxxxx>
>> ---
>> arch/x86/kvm/cpuid.c | 16 ++++++++++++++++
>> arch/x86/kvm/x86.c | 1 +
>> 2 files changed, 17 insertions(+)
>>
>> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
>> index 6525e92..f8ddca6 100644
>> --- a/arch/x86/kvm/cpuid.c
>> +++ b/arch/x86/kvm/cpuid.c
>> @@ -62,6 +62,7 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu)
>> {
>> struct kvm_cpuid_entry2 *best;
>> struct kvm_lapic *apic = vcpu->arch.apic;
>> + bool vendor_intel = false;
>>
>> best = kvm_find_cpuid_entry(vcpu, 1, 0);
>> if (!best)
>> @@ -114,6 +115,21 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu)
>> vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu);
>>
>> kvm_pmu_refresh(vcpu);
>> +
>> + /* Don't expose syscall/sysret to intel non 64-bit mode guest */
>> + best = kvm_find_cpuid_entry(vcpu, 0x00000000, 0x00000000);
>> + if (best && best->ebx == 0x756e6547 && best->ecx == 0x6c65746e &&
>> + best->edx == 0x49656e69)
>> + vendor_intel = true;
>
> You can use X86EMUL_CPUID_VENDOR_GenuineIntel_ebx/ecx/edx instead here.
Ok.
>
>> + best = kvm_find_cpuid_entry(vcpu, 0x80000001, 0);
>> + if (best && vendor_intel) {
>> + if (!is_long_mode(vcpu))
>> + best->edx &= ~F(SYSCALL);
>> + else
>> + best->edx |= F(SYSCALL);
>
> This is not correct. As far as I know, the SYSCALL bit is always
> present in CPUID, even if the machine is running in 32-bit mode; CPUID
> documentation (SDM Volume 2) explicitly documents bit 11 as "Bit 11:
> SYSCALL/SYSRET available in 64-bit mode".
No, I try a 32-bit linux host kernel, cpuid tool shows that SYSCALL
bit is not set.
>
> So there are two possibilities here:
>
> 1) Clear F(SYSCALL) in kvm_update_cpuid, like you are doing here but
> only if F(LM) is already clear (in addition to the vendor being Intel).
Good point. :-)
>
> 2) do nothing, declare this a userspace bug. Linux knows that only AMD
> machines support SYSCALL in 32-bit mode (there is a separate feature bit
> X86_FEATURE_SYSCALL32 that is only set by arch/x86/kernel/cpu/amd.c).
> Are you fixing an issue with Windows? If so, with what QEMU command
No.
> line? But if it's not an issue with a real guest, doing nothing would
> be my favorite option...
>
> In any case, set_efer doesn't need to call kvm_update_cpuid.
Btw, I also try a 32-bit linux guest in vmware on my macbook, it also
doesn't expose
syscall/sysret.
Regards,
Wanpeng Li
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