pkeys: Reserve PKEY_DISABLE_READ
Florian Weimer
fweimer at redhat.com
Fri Nov 9 07:23:35 AEDT 2018
* Ram Pai:
> Florian,
>
> I can. But I am struggling to understand the requirement. Why is
> this needed? Are we proposing a enhancement to the sys_pkey_alloc(),
> to be able to allocate keys that are initialied to disable-read
> only?
Yes, I think that would be a natural consequence.
However, my immediate need comes from the fact that the AMR register can
contain a flag combination that is not possible to represent with the
existing PKEY_DISABLE_WRITE and PKEY_DISABLE_ACCESS flags. User code
could write to AMR directly, so I cannot rule out that certain flag
combinations exist there.
So I came up with this:
int
pkey_get (int key)
{
if (key < 0 || key > PKEY_MAX)
{
__set_errno (EINVAL);
return -1;
}
unsigned int index = pkey_index (key);
unsigned long int amr = pkey_read ();
unsigned int bits = (amr >> index) & 3;
/* Translate from AMR values. PKEY_AMR_READ standing alone is not
currently representable. */
if (bits & PKEY_AMR_READ)
return PKEY_DISABLE_ACCESS;
else if (bits == PKEY_AMR_WRITE)
return PKEY_DISABLE_WRITE;
return 0;
}
And this is not ideal. I would prefer something like this instead:
switch (bits)
{
case PKEY_AMR_READ | PKEY_AMR_WRITE:
return PKEY_DISABLE_ACCESS;
case PKEY_AMR_READ:
return PKEY_DISABLE_READ;
case PKEY_AMR_WRITE:
return PKEY_DISABLE_WRITE;
case 0:
return 0;
}
By the way, is the AMR register 64-bit or 32-bit on 32-bit POWER?
Thanks,
Florian
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