From: Steven Price

Sent: 24 May 2021 12:21

...

So a "generic" way of requested the kernel limit the address space for
allocations would be potentially useful for other purposes. Adding a new
syscall for this purpose would be sensible. We already have (at least)
two "hacks" in mmap for controlling the address range that can be used:

 * MAP_32BIT - x86 only, and really "31 bit"

 * Providing a mmap() hint with the top bits set to opt-in to 52-bit VAs.

A well defined mechanism for controlling the valid VA range for
allocations would be much better than adding more hacks - and bonus
points if it works for all the different types of allocation unlike the
above.

I'd have thought a 'MAP_BELOW' flag (cf MAP_FIXED) would suffice.
I'm sort of surprised MAP_32BIT wasn't implemented that way.
'man mmap' says MAP_32BIT was added for x64 thread stacks - I though
the requirement can from 32bit wine (windows has a 2G user/kernel boundary).

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel