Re: [PATCH RFC] cache: Make cpu_cache_invalidate_memregion() error out if there are no handlers

[Bence Csókás]

Hi,

On 2026. 09. 23. 4:18, Andrew Morton wrote:
> On Tue, 22 Sep 2026 09:29:31 +0200 Bence Csokas <bence.csokas@xxxxxxx> wrote:
>
> > Currently, if there are no registered handlers,
> > cpu_cache_invalidate_memregion() returns 0. Callers are expected to check
> > cpu_cache_has_invalidate_memregion() and return -ENXIO themselves, instead
> > of calling this function. If a caller forgets to do this, they may
> > erroneously think the operation succeeded. This is in contrast to x86,
> > where cpu_cache_invalidate_memregion() itself checks if the operation is
> > supported, and returns -ENXIO if it is not.
>
> Do you expect any callers to be altered as a result of this change?
>
> If so, full details would be helpful.

Current callers, not necessarily. Future callers, maybe.

Presently, as far as I see, there are 2 consumers: CXL and NVDIMM, with 
3 call sites in total.

2 of these call sites [1] [2] are in the form of:

	if (!has_invalidate()) {
		if (TEST)
			return 0;
		return -ENXIO;
	}
	invalidate();

These types of call sites can stay as-is.

The remaining one [3] is in a void function, and in the form:

	if (has_invalidate())
		invalidate();

Lastly, while not a consumer, here's what x86 [4] does. It's possible a 
future caller will want to replicate this:

	if (!has_invalidate())
		return -ENXIO;
	invalidate();

These types of call sites can do away with calling has_invalidate() 
going forward.

[1] 
https://elixir.bootlin.com/linux/v7.3-rc3/source/drivers/cxl/core/region.c#L242
[2] 
https://elixir.bootlin.com/linux/v7.3-rc3/source/drivers/nvdimm/region_devs.c#L93
[3] 
https://elixir.bootlin.com/linux/v7.3-rc3/source/drivers/nvdimm/region.c#L113
[4] 
https://elixir.bootlin.com/linux/v7.3-rc3/source/arch/x86/mm/pat/set_memory.c#L372

Bence