Re: [Qemu-devel] [PATCH 2/2] Expose tsc deadline timer cpuid to guest

[Liu, Jinsong]

Rik van Riel wrote:
> On 03/09/2012 01:27 PM, Liu, Jinsong wrote:
> 
>> As for 'tsc deadline' feature exposing, my patch (as attached) just
>> obey qemu general cpuid exposing method, and also satisfied your
>> target I think.  
> 
> One question.
> 
> Why is TSC_DEADLINE not exposed in the cpuid allowed feature
> bits in do_cpuid_ent() in arch/x86/kvm/x86.c ?
> 
>          /* cpuid 1.ecx */
>          const u32 kvm_supported_word4_x86_features =
>                  F(XMM3) | F(PCLMULQDQ) | 0 /* DTES64, MONITOR */ |
>                  0 /* DS-CPL, VMX, SMX, EST */ |
>                  0 /* TM2 */ | F(SSSE3) | 0 /* CNXT-ID */ | 0 /*
> Reserved */ |
>                  F(FMA) | F(CX16) | 0 /* xTPR Update, PDCM */ |
>                  0 /* Reserved, DCA */ | F(XMM4_1) |
>                  F(XMM4_2) | F(X2APIC) | F(MOVBE) | F(POPCNT) |
>                  0 /* Reserved*/ | F(AES) | F(XSAVE) | 0 /* OSXSAVE
> */ | F(AVX) |
>                  F(F16C) | F(RDRAND);
> 
> Would it make sense to expose F(TSC_DEADLINE) above?
> 
> Or is there something truly special about tsc deadline
> that means it should be different from everything else?

Because the feature depends on KVM_CREATE_IRQCHIP, which we cannot guarantee 
will be called, we expose it via a KVM_CAP_TSC_DEADLINE_TIMER and not 
KVM_GET_SUPPORTED_CPUID.
Refer changeset 4d25a066b69fb749a39d0d4c610689dd765a0b0e.

BTW, your question remind me qemu-kvm side patch, and I update it a little 
(would be sent out later).

Thanks,
Jinsong