Re: [RFC] Kernel Support of Memory Error Detection.

["HORIGUCHI NAOYA(堀口 直也)" <naoya.horiguchi@nec.com>]

On Tue, Nov 08, 2022 at 04:17:06PM +0000, Luck, Tony wrote:
> > If it is feasible in future that hardware vendors can make patrol
> > scrubber programmable, we can even direct the scanning to patrol
> > scrubber.
> 
> There was an attempt to create an ACPI interface for this. I don't know if it made
> it into the standard.

I briefly checked the latest ACPI spec, and it seems that some interfaces
to control (h/w based) patrol scrubbing are defined.

https://uefi.org/specs/ACPI/6.5/05_ACPI_Software_Programming_Model.html#acpi-ras-feature-table-rasf

> I didn't do anything with it for Linux because the interface was
> quite complex.
> 
> From a h/w perspective it might always be complex. Consecutive system physical
> addresses are generally interleaved across multiple memory controllers, channels,
> DIMMs and ranks. While patrol scrubbing may be done by each memory controller
> at the channel level.
> 
> So a simple request to scan a few megabytes of system physical address would
> require address translation to figure out the channel addresses on each of the
> memory controllers and programming each to scan the pieces they contribute to
> the target range.

I expect that the physical address visible to the kernel is transparently
translated to the real address in which DIMM in which channel.

- Naoya Horiguchi