Re: [GIT preview] for-6.3/cxl-ram-region

[Gregory Price <gregory.price@memverge.com>]

On Thu, Feb 02, 2023 at 10:18:33AM -0800, Dan Williams wrote:
> Gregory Price wrote:
> [..]
> > To me, the solution here isn't to change QEMU, it's to change the kernel
> > to try to get it to aggressively keep executable regions out of CXL by
> > marking CXL regions into a new zone type that essentially says "Use this
> > as a last resort only for X pages".  But that would likely require
> > adding migration code to the likes of mprotect and friends.
> 
> No, this can't be the path forward as far as I can see. QEMU is a test
> vehicle for CXL enabling, there's no expectation that QEMU is running
> CXL emulation in production. The quirks of how the QEMU-CXL memory
> behaves are not something the kernel should worry about mitigating. CXL
> is "System RAM" especially in the case when it is mapped by
> platform-firmware. If it's not suitable to be treated as "System RAM"
> then the onus is on platform-firmware to keep it out of the general
> purpose pool.
> 

Eh, you're right, just spitballing.  On real hardware this isn't an
issue so there's no reason to change the kernel.  QEMU should just model
the hardware.