[PATCH 1/2] RISC-V: mm: Restrict address space for sv39,sv48,sv57

[Nick Kossifidis]

On 6/28/23 02:36, Palmer Dabbelt wrote:
> On Tue, 27 Jun 2023 15:32:36 PDT (-0700), jrtc27 at jrtc27.com wrote:
>> On 27 Jun 2023, at 23:21, Charlie Jenkins <charlie at rivosinc.com> wrote:
>>>
>>> Make sv39 the default address space for mmap as some applications
>>> currently depend on this assumption.
>>
>> They are just plain wrong too. Sv48 was in even Priv v1.10 (the first
>> spec where satp was named as such and contained the mode, rather than
>> requiring M-mode’s help in configuring virtual memory), predating the
>> ratified v1.11 spec. A 39-bit address space is pathetic and has
>> implications for ASLR.
>>
>> I strongly suggest applications be forced to support at least Sv48,
>> which is totally reasonable given the address space sizes used by other
>> architectures. Sv57 is more disruptive to some runtimes, though ideally
>> even that would be free for the kernel to use rather than committing to
>> not using it for the default uABI.
> 
> Go and OpenJDK both broke when we expanded the VA width.  I don't like 
> it either, but if the change breaks userspace then it's a regression and 
> we have to live with the bug.
> 

Have we debugged this ? do we at least know why they break ? Just 
disabling Sv48/57 by default for everyone because some userspace apps 
break doesn't seem the correct approach, it seems more like a bug in 
userspace IMHO.