Re: [RFCv2 00/10] Linear Address Masking enabling

Dave Hansen
2022-05-12T21:53:06Z

On 5/12/22 12:39, Thomas Gleixner wrote:
>> It's OK for a debugging build that runs on one kind of hardware. But,
>> if we want LAM-using binaries to be portable, we have to do something
>> different.
>>
>> One of the stated reasons for adding LAM hardware is that folks want to
>> use sanitizers outside of debugging environments. To me, that means
>> that LAM is something that the same binary might run with or without.
> On/off yes, but is there an actual use case where such a mechanism would
> at start time dynamically chose the number of bits?

I'd love to hear from folks doing the userspace side of this. Will
userspace be saying: "Give me all the bits you can!". Or, will it
really just be looking for 6 bits only, and it doesn't care whether it
gets 6 or 15, it will use only 6?

Do the sanitizers have more overhead with more bits? Or *less* overhead
because they can store more metadata in the pointers?

Will anyone care about the difference about potentially missing 1/64
issues with U57 versus 1/32768 with U48?