Re: [Xen-devel] [PATCH v2 05/13] intel/VPMU: Clean up Intel VPMU code

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 20.09.13 at 11:42, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> wrote:
> +void vmx_rm_guest_msr(u32 msr)
> +{
> +    struct vcpu *curr = current;
> +    unsigned int i, 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;
> +    
> +    for ( i = idx; i < msr_count - 1; i++ )

"idx" not being used further down anymore, why do you need
another loop variable here?

> +    {
> +        msr_area[i].index = msr_area[i + 1].index;
> +        rdmsrl(msr_area[i].index, msr_area[i].data);

This is clearly a side effect of the function call no-one would
expect. Why do you do this?

> +    }
> +    msr_area[msr_count - 1].index = 0;
> +
> +    curr->arch.hvm_vmx.msr_count = --msr_count;
> +    __vmwrite(VM_EXIT_MSR_STORE_COUNT, msr_count);
> +    __vmwrite(VM_ENTRY_MSR_LOAD_COUNT, msr_count);
> +
> +    return;

Pointless "return".

All the same comments apply to vmx_rm_host_load_msr().

> +static int arch_pmc_cnt; /* Number of general-purpose performance counters */
> +static int fixed_pmc_cnt; /* Number of fixed performance counters */

unsigned? __read_mostly?

> @@ -248,13 +230,13 @@ static void core2_vpmu_set_msr_bitmap(unsigned long 
> *msr_bitmap)
>      int i;
>  
>      /* Allow Read/Write PMU Counters MSR Directly. */
> -    for ( i = 0; i < core2_fix_counters.num; i++ )
> +    for ( i = 0; i < fixed_pmc_cnt; i++ )
>      {
> -        clear_bit(msraddr_to_bitpos(core2_fix_counters.msr[i]), msr_bitmap);
> -        clear_bit(msraddr_to_bitpos(core2_fix_counters.msr[i]),
> +        clear_bit(msraddr_to_bitpos(MSR_CORE_PERF_FIXED_CTR0 + i), 
> msr_bitmap);
> +        clear_bit(msraddr_to_bitpos(MSR_CORE_PERF_FIXED_CTR0 + i),

Dropping the static array will make the handling here quite a bit more
complicated should there ever appear a second dis-contiguous MSR
range.

> @@ -262,32 +244,37 @@ static void core2_vpmu_set_msr_bitmap(unsigned long 
> *msr_bitmap)
>      }
>  
>      /* Allow Read PMU Non-global Controls Directly. */
> -    for ( i = 0; i < core2_ctrls.num; i++ )
> -        clear_bit(msraddr_to_bitpos(core2_ctrls.msr[i]), msr_bitmap);
> -    for ( i = 0; i < core2_get_pmc_count(); i++ )
> +    for ( i = 0; i < arch_pmc_cnt; i++ )
>          clear_bit(msraddr_to_bitpos(MSR_P6_EVNTSEL0+i), msr_bitmap);
> +
> +    clear_bit(msraddr_to_bitpos(MSR_CORE_PERF_FIXED_CTR_CTRL), msr_bitmap);
> +    clear_bit(msraddr_to_bitpos(MSR_IA32_PEBS_ENABLE), msr_bitmap);
> +    clear_bit(msraddr_to_bitpos(MSR_IA32_DS_AREA), msr_bitmap);

As you can see, this is already the case here.

The patch description doesn't really say _why_ you do this.
Jan


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