Re: [RFC PATCH 8/9] um: nommu: add userspace runner processes

[Hajime Tazaki <thehajime@gmail.com>]

On Tue, 21 Jul 2026 03:26:58 +0900,
Johannes Berg wrote:
> 
> From: Johannes Berg <johannes.berg@intel.com>
> 
> For NOMMU there are not separate address spaces for
> each userspace process group, which on the one hand
> means we cannot start them on demand, but on the
> other means we can just have one for each (virtual)
> CPU, and map all of the memory into them.
> 
> Implement such processes, and the remaining bits
> needed to compile the kernel without CONFIG_MMU.

I was wondering where kernel address is located in this mode.

although it doesn't have to be, under nommu, kernel address is located
in the same address space with all userspace processes in my
understanding.

the kernel address is accessible (danger but it's !MMU) from userspace
thus __access_ok() always returns 1.  so just wondering what is the
case with this runner process approach.

a program accessing kernel address may fail (or crash in some case),
but with the runner it won't ?

-- Hajime