Re: [Xen-devel] [PATCH 06/10] x86/hvm: pkeys, add functions to get pkeys value from PTE

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.11.15 at 15:16, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 16/11/15 10:31, Huaitong Han wrote:
>> +#define _PAGE_PKEY_BIT0 19       /* Protection Keys, bit 1/4 */
>> +#define _PAGE_PKEY_BIT1 20       /* Protection Keys, bit 2/4 */
>> +#define _PAGE_PKEY_BIT2 21       /* Protection Keys, bit 3/4 */
>> +#define _PAGE_PKEY_BIT3 22       /* Protection Keys, bit 4/4 */
>> +
>> +#define get_pte_pkeys(x) ((int)(get_pte_flags(x) >> _PAGE_PKEY_BIT0) & 0xF)
> 
> Please implemented these as masks, for consistency with the other
> _PAGE_* entries.  I would recommend also having a _SHIFT and _MASK define.

Since _SHIFT can always be calculated from _MASK, and since
we have MASK_{INSR,EXTR}(), I'd prefer just _MASK ones to
be added, unless this results in significantly less readable code.

>> +
>>  /* Bit 23 of a 24-bit flag mask. This corresponds to bit 63 of a pte.*/
>>  #define _PAGE_NX_BIT (1U<<23)
>>  
> 
> There is however another issue. Xen currently uses bit 62 for software
> purposes, which is incompatible with enabling PKE.  _PAGE_GNTTAB needs
> moving to a different, software-available bit.  I would recommend bit 13
> of flags, adjacent to _PAGE_GUEST_KERNEL which is our other
> software-used flag.

Can we in fact do that? _PAGE_GNTTAB is visible to PV guests, and
those guests need to avoid using that flag for their own purposes.

Jan


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