Re: [PATCH] x86/mtrr: Drop workaround for old 32bit CPUs

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 08/07/2020 11:48, Roger Pau Monné wrote:
> On Wed, Jul 08, 2020 at 11:14:43AM +0100, Andrew Cooper wrote:
>> This logic is dead as Xen is 64bit-only these days.
>>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Thanks,

>> ---
>> CC: Jan Beulich <JBeulich@xxxxxxxx>
>> CC: Wei Liu <wl@xxxxxxx>
>> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>> ---
>>  xen/arch/x86/cpu/mtrr/generic.c | 17 -----------------
>>  1 file changed, 17 deletions(-)
>>
>> diff --git a/xen/arch/x86/cpu/mtrr/generic.c 
>> b/xen/arch/x86/cpu/mtrr/generic.c
>> index 89634f918f..06fa0c0420 100644
>> --- a/xen/arch/x86/cpu/mtrr/generic.c
>> +++ b/xen/arch/x86/cpu/mtrr/generic.c
>> @@ -570,23 +570,6 @@ int generic_validate_add_page(unsigned long base, 
>> unsigned long size, unsigned i
>>  {
>>      unsigned long lbase, last;
>>  
>> -    /*  For Intel PPro stepping <= 7, must be 4 MiB aligned 
>> -        and not touch 0x70000000->0x7003FFFF */
>> -    if (is_cpu(INTEL) && boot_cpu_data.x86 == 6 &&
>> -        boot_cpu_data.x86_model == 1 &&
>> -        boot_cpu_data.x86_mask <= 7) {
>> -            if (base & ((1 << (22 - PAGE_SHIFT)) - 1)) {
>> -                    printk(KERN_WARNING "mtrr: base(%#lx000) is not 4 MiB 
>> aligned\n", base);
>> -                    return -EINVAL;
>> -            }
>> -            if (!(base + size < 0x70000 || base > 0x7003F) &&
>> -                (type == MTRR_TYPE_WRCOMB
>> -                 || type == MTRR_TYPE_WRBACK)) {
>> -                    printk(KERN_WARNING "mtrr: writable mtrr between 
>> 0x70000000 and 0x7003FFFF may hang the CPU.\n");
>> -                    return -EINVAL;
>> -            }
>> -    }
>> -
>>      /*  Check upper bits of base and last are equal and lower bits are 0
>>          for base and 1 for last  */
>>      last = base + size - 1;
> FWIW, you could also initialize last at definition time.

I've got some very different cleanup in mind for that code, seeing as it
can be simplified to a single test expression.

~Andrew