24 Mar
2021
24 Mar
'21
4:34 p.m.
On 3/24/21 3:05 AM, Thomas Hellström (Intel) wrote:
Yes, I agree. Seems like the special (SW1) is available also for huge page table entries on x86 AFAICT, although just not implemented. Otherwise the SW bits appear completely used up.
Although the _PAGE_BIT_SOFTW* bits are used up, there's plenty of room in the hardware PTEs. Bits 52->58 are software-available, and we're only using 58 at the moment.
We also have not been careful at *all* about how _PAGE_BIT_SOFTW* are used. It's quite possible we can encode another use even in the existing bits.
Personally, I'd just try:
#define _PAGE_BIT_SOFTW5 57 /* available for programmer */