Re: [Xen-devel] [PATCH RFC 2/9] xen: Optimize introspection access to guest state

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

On 07/02/2014 06:31 PM, Andrew Cooper wrote:
> On 02/07/14 14:33, Razvan Cojocaru wrote:
>> diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
>> index 2caa04a..fed21b6 100644
>> --- a/xen/arch/x86/hvm/vmx/vmx.c
>> +++ b/xen/arch/x86/hvm/vmx/vmx.c
>> @@ -425,6 +425,7 @@ static void vmx_vmcs_save(struct vcpu *v, struct 
>> hvm_hw_cpu *c)
>>      c->cr4 = v->arch.hvm_vcpu.guest_cr[4];
>>  
>>      c->msr_efer = v->arch.hvm_vcpu.guest_efer;
>> +    c->guest_x86_mode = vmx_guest_x86_mode(v);
> 
> guest_x86_mode is a linear function of cr0, eflags and efer.  It can be
> calculated by userspace doesn't need to transmitted individually.

OK, but 1) I'm not sending eflags into userspace, and 2) I thought Xen's
vmx_guest_x86_mode() function is more trustworthy than an userspace
translation of it, with not much overhead for the HV.

1) also means that I'd replace guest_x86_mode in the mem_event with efer
and not gain more space in the ring buffer.

Hope I understood your comment correctly.


Thanks,
Razvan Cojocaru

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