Re: [Qemu-devel] [PATCH] target-i386: kvm: Don't enable MONITOR by default on any CPU model

[Paolo Bonzini]

Il 30/04/2014 03:11, Marcelo Tosatti ha scritto:
> On Tue, Apr 29, 2014 at 06:17:17PM -0300, Eduardo Habkost wrote:
>> KVM never supported the MONITOR flag so it doesn't make sense to have it
>> enabled by default when KVM is enabled.
>>
>> The rationale here is similar to the cases where it makes sense to have
>> a feature enabled by default on all CPU models when on KVM mode (e.g.
>> x2apic). In this case we are having a feature disabled by default for
>> the same reasons.
>>
>> In this case we don't need machine-type compat code because it is
>> currently impossible to run a KVM VM with the MONITOR flag set.
>>
>> Signed-off-by: Eduardo Habkost <address@hidden>
> 
> Why relying on the kernel filtering is not sufficient ? 

Because that would break "-cpu ...,enforce".  In fact many old models 
are currently broken because they were never tested with "-cpu 
...,enforce".  For example:

$ qemu-system-x86_64 -cpu core2duo,enforce --enable-kvm
warning: host doesn't support requested feature: CPUID.01H:EDX.ds [bit 21]
warning: host doesn't support requested feature: CPUID.01H:EDX.acpi [bit 22]
warning: host doesn't support requested feature: CPUID.01H:EDX.ht [bit 28]
warning: host doesn't support requested feature: CPUID.01H:EDX.tm [bit 29]
warning: host doesn't support requested feature: CPUID.01H:EDX.pbe [bit 31]
warning: host doesn't support requested feature: CPUID.01H:ECX.dtes64 [bit 2]
warning: host doesn't support requested feature: CPUID.01H:ECX.monitor [bit 3]
warning: host doesn't support requested feature: CPUID.01H:ECX.ds_cpl [bit 4]
warning: host doesn't support requested feature: CPUID.01H:ECX.vmx [bit 5]
warning: host doesn't support requested feature: CPUID.01H:ECX.est [bit 7]
warning: host doesn't support requested feature: CPUID.01H:ECX.tm2 [bit 8]
warning: host doesn't support requested feature: CPUID.01H:ECX.xtpr [bit 14]
warning: host doesn't support requested feature: CPUID.01H:ECX.pdcm [bit 15]
qemu-system-x86_64: Host's CPU doesn't support requested features


Paolo