On Thu, Aug 29, 2024 at 09:54:08AM -0700, Dave Hansen wrote:
On 8/28/24 13:15, Charlie Jenkins wrote:
A way to restrict mmap() to return LAM compliant addresses in an entire address space also doesn't have to be mutually exclusive with this flag. This flag allows for the greatest degree of control from applications. I don't believe there is additionally performance saving that could be achieved by having this be on a per address space basis.
I agree with you in general. The MAP_BELOW_HINT _is_ the most flexible. But it's also rather complicated.
Can you expand upon what you mean by it being complicated? Complicated for the kernel or complicated for a user?
My _hope_ would be that a per-address-space property could share at least some infrastructure with what x86/LAM and arm/TBI do to the address space. Basically put the restrictions in place for purely software reasons instead of the mostly hardware reasons for LAM/TBI.
That is a good point, perhaps that would be a way to hook this into LAM, TBI, and any other architecture's specific address masking feature.
- Charlie
Lorenzo also raised some very valid points about a having a generic address-restriction ABI. I'm certainly not discounting those concerns. It's not something that can be done lightly.