Re: [Xen-devel] [PATCH v9 05/20] intel/VPMU: Clean up Intel VPMU code

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 08.08.14 at 18:55, <boris.ostrovsky@xxxxxxxxxx> wrote:
> --- a/xen/arch/x86/hvm/vmx/vmcs.c
> +++ b/xen/arch/x86/hvm/vmx/vmcs.c
> @@ -1208,6 +1208,32 @@ int vmx_add_guest_msr(u32 msr)
>      return 0;
>  }
>  
> +void vmx_rm_guest_msr(u32 msr)
> +{
> +    struct vcpu *curr = current;
> +    unsigned int idx, msr_count = curr->arch.hvm_vmx.msr_count;
> +    struct vmx_msr_entry *msr_area = curr->arch.hvm_vmx.msr_area;
> +
> +    if ( msr_area == NULL )
> +        return;
> +
> +    for ( idx = 0; idx < msr_count; idx++ )
> +        if ( msr_area[idx].index == msr )
> +            break;
> +
> +    if ( idx == msr_count )
> +        return;

This absence check (producing success) together with the presence
check in the corresponding "add" function (also producing success) is
certainly bogus without reference counting: Two independent callers
of "add" would each validly assume they ought to call "rm" when done
with their job, taking away the control over the MSR from the other.
Yet if you don't think of independent callers, these presence/absence
checks don't make sense at all.

Jan


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