[RFC v7 02/25] powerpc: track allocation status of all pkeys

[Ram Pai]

On Thu, Aug 10, 2017 at 05:25:39PM -0300, Thiago Jung Bauermann wrote:
> 
> Ram Pai <linuxram at us.ibm.com> writes:
> >  static inline void pkey_initialize(void)
> >  {
> > +	int os_reserved, i;
> > +
> >  	/* disable the pkey system till everything
> >  	 * is in place. A patch further down the
> >  	 * line will enable it.
> >  	 */
> >  	pkey_inited = false;
> > +
> > +	/* Lets assume 32 keys */
> > +	pkeys_total = 32;
> > +
> > +#ifdef CONFIG_PPC_4K_PAGES
> > +	/*
> > +	 * the OS can manage only 8 pkeys
> > +	 * due to its inability to represent
> > +	 * them in the linux 4K-PTE.
> > +	 */
> > +	os_reserved = pkeys_total-8;
> > +#else
> > +	os_reserved = 0;
> > +#endif
> > +	/*
> > +	 * Bits are in LE format.
> > +	 * NOTE: 1, 0 are reserved.
> > +	 * key 0 is the default key, which allows read/write/execute.
> > +	 * key 1 is recommended not to be used.
> > +	 * PowerISA(3.0) page 1015, programming note.
> > +	 */
> > +	initial_allocation_mask = ~0x0;
> > +	for (i = 2; i < (pkeys_total - os_reserved); i++)
> > +		initial_allocation_mask &= ~(0x1<<i);
> >  }
> >  #endif /*_ASM_PPC64_PKEYS_H */
> 
> In v6, key 31 was also reserved, but it's not in this version. Is this
> intentional?

On powernv platform, there is no hypervisor and hence the hypervisor
will not reserve key 31 for its own use. Wherease on PAPR guest
the hypervisor takes away key 31.  

Its not possible to determine at compile time which keys are used
or not. Hence the above code.  pkeys_total is 32 in this patch,
but will be set to whatever value the device tree tells us. That will
be done in a subsequent patch.


RP