Re: [Xen-devel] [PATCH 2/3] x86/pv: Introduce and use x86emul_write_dr()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 13/04/18 09:39, Jan Beulich wrote:
>>>> On 12.04.18 at 18:55, <andrew.cooper3@xxxxxxxxxx> wrote:
>> @@ -2029,7 +2035,17 @@ long set_debugreg(struct vcpu *v, unsigned int reg, 
>> unsigned long value)
>>          if ( v == curr )
>>              write_debugreg(3, value);
>>          break;
>> +
>> +    case 4:
>> +        if ( v->arch.pv_vcpu.ctrlreg[4] & X86_CR4_DE )
>> +            return -ENODEV;
>> +
>> +        /* Fallthrough */
>>      case 6:
>> +        /* The upper 32 bits are strictly reserved. */
>> +        if ( value != (uint32_t)value )
>> +            return -EINVAL;
>> +
>>          /*
>>           * DR6: Bits 4-11,16-31 reserved (set to 1).
>>           *      Bit 12 reserved (set to 0).
> How are the upper 32 bits different from the other reserved bits (named in the
> comment visible here)?

The upper 32 bits are MBZ and will raise #GP if set.  The lower reserved
bits are write-ignored.

~Andrew

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