On Wed, Feb 24, 2016 at 06:39:22PM +0100, Alexander Graf wrote:
On 02/24/2016 02:37 PM, Mark Rutland wrote:
On Wed, Feb 24, 2016 at 01:11:35PM +0100, Alexander Graf wrote:
- /* Calculate the maximum physical (and thus virtual) address */
- if (max_addr > (1ULL << 44)) {
ips = 5;va_bits = 48;- } else if (max_addr > (1ULL << 42)) {
ips = 4;va_bits = 44;- } else if (max_addr > (1ULL << 40)) {
ips = 3;va_bits = 42;- } else if (max_addr > (1ULL << 36)) {
ips = 2;va_bits = 40;- } else if (max_addr > (1ULL << 32)) {
ips = 1;va_bits = 36;- } else {
ips = 0;va_bits = 32;- }
In Linux we program IPS to the maximum PARange from ID_AA64MMFR0.
If you did the same here you wouldn't have to iterate over all the memory map entries to determine the maximum PA you care about (though you may still need to do that for the VA size).
Since we'd want to find the largest number for VA to trim one level of page table if we can, I don't see how it would buy is much to take the maximum supported PARange of the core into account.
It would simply be a saving of lines, as you'd program the same IPS value regardless of max_addr (and you have to expect that PARange is sufficient regardless).
Otherwise, yes, it doesn't buy you anything.
Thanks, Mark.