Re: [PATCH] svm: Do not intercept RDTCS(P) when TSC scaling is supported by hardware

[Keir Fraser <keir@xen.org>]

On 20/04/2012 09:05, "Keir Fraser" <keir.xen@gmail.com> wrote:

> On 20/04/2012 03:21, "Boris Ostrovsky" <boris.ostrovsky@amd.com> wrote:
> 
>> # HG changeset patch
>> # User Boris Ostrovsky <boris.ostrovsky@amd.com>
>> # Date 1334875170 14400
>> # Node ID 55bf11ebce87ceb73fb2c372dcef170ec0bb4a18
>> # Parent  7c777cb8f705411b77c551f34ba88bdc09e38ab8
>> svm: Do not intercept RDTCS(P) when TSC scaling is supported by hardware
>> 
>> When running in TSC_MODE_ALWAYS_EMULATE mode on processors that support
>> TSC scaling we don't need to intercept RDTSC/RDTSCP instructions.
>> 
>> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@amd.com>
>> Acked-by: Wei Huang <wei.huang2@amd.com>
>> Tested-by: Wei Huang <wei.huang2@amd.com>
> 
> Worth an ack/nack from Dan M I'd say. He'll probably have some comment about
> possible cross-CPU TSC skew.

Oh, and apart from that, we're also in feature freeze for 4.2, and this
isn't a bug fix. Similarly, it's not really a candidate for the stable 4.1
branch either, at any time.

 -- Keir

>  -- Keir
> 
>> diff -r 7c777cb8f705 -r 55bf11ebce87 xen/arch/x86/hvm/svm/svm.c
>> --- a/xen/arch/x86/hvm/svm/svm.c Wed Apr 18 16:49:55 2012 +0100
>> +++ b/xen/arch/x86/hvm/svm/svm.c Thu Apr 19 18:39:30 2012 -0400
>> @@ -724,12 +724,18 @@ static void svm_set_rdtsc_exiting(struct
>>  {
>>      struct vmcb_struct *vmcb = v->arch.hvm_svm.vmcb;
>>      u32 general1_intercepts = vmcb_get_general1_intercepts(vmcb);
>> +    u32 general2_intercepts = vmcb_get_general2_intercepts(vmcb);
>>  
>>      general1_intercepts &= ~GENERAL1_INTERCEPT_RDTSC;
>> -    if ( enable )
>> +    general2_intercepts &= ~GENERAL2_INTERCEPT_RDTSCP;
>> +
>> +    if ( enable && !cpu_has_tsc_ratio ) {
>>          general1_intercepts |= GENERAL1_INTERCEPT_RDTSC;
>> +        general2_intercepts |= GENERAL2_INTERCEPT_RDTSCP;
>> +    }
>>  
>>      vmcb_set_general1_intercepts(vmcb, general1_intercepts);
>> +    vmcb_set_general2_intercepts(vmcb, general2_intercepts);
>>  }
>>  
>>  static unsigned int svm_get_insn_bytes(struct vcpu *v, uint8_t *buf)
>> 
> 
>