On Wed, Feb 18, 2015 at 11:27 AM, Ingo Molnar <mi...@kernel.org> wrote: > > * Dan Williams <dan.j.willi...@intel.com> wrote: > >> On Wed, Feb 18, 2015 at 10:53 AM, Ingo Molnar <mi...@kernel.org> wrote: >> > >> > * Dan Williams <dan.j.willi...@intel.com> wrote: >> > >> >> On Wed, Feb 18, 2015 at 10:30 AM, Ingo Molnar <mi...@kernel.org> wrote: >> >> > >> >> > * Dan Williams <dan.j.willi...@intel.com> wrote: >> >> > >> >> >> On Tue, Feb 17, 2015 at 12:42 AM, Boaz Harrosh <b...@plexistor.com> >> >> >> wrote: >> >> >> > On 02/17/2015 12:03 AM, Matthew Wilcox wrote: >> >> >> >> On Mon, Feb 16, 2015 at 01:07:07PM +0200, Boaz Harrosh wrote: >> >> >> >>> In any way this is a problem for the new type-12 NvDIMM memory >> >> >> >>> chips that >> >> >> >>> are circulating around. (It is estimated that there are already >> >> >> >>> 100ds of >> >> >> >>> thousands NvDIMM chips in active use) >> >> >> >> >> >> >> >> Hang on. NV-DIMM chips don't know anyhing about E820 >> >> >> >> tables. They don't have anything in them that says "I >> >> >> >> am type 12!". How they are reported is up to the >> >> >> >> BIOS. Just because your BIOS vendor has chosen to >> >> >> >> report tham as type 12 doesn't mean that any other >> >> >> >> BIOS vedor is going to have done the same thing. >> >> >> >> >> >> >> >> Fortunately, the BIOS people have all got together and >> >> >> >> decided what they're going to do, and it's not type >> >> >> >> 12. Unfortunately, I think I'm bound by various >> >> >> >> agreements to not say what they are going to do until >> >> >> >> they do. But putting this temporary workaround in the >> >> >> >> kernel to accomodate one BIOS vendor's unreleased >> >> >> >> experimental code seems like entirely the wrong idea. >> >> >> >> >> >> >> > >> >> >> > I had a feeling I'm entering an holy war ;-). >> >> >> > >> >> >> > I hope you are OK with my first patch. That an unknown >> >> >> > type need not be reported busy, and behave same as >> >> >> > "reserved"? >> >> >> >> >> >> No, it seems the safe thing to do is prevent the >> >> >> kernel from accessing any memory that it does not know >> >> >> the side-effects of accessing. >> >> > >> >> > Well, except when the kernel does know how to access >> >> > it: when an nvdimm driver knows about its own memory >> >> > region and knows how to handle it, right? >> >> >> >> Yes, except that "type-12" is something picked out of the >> >> air that may be invalidated by a future spec change. >> >> >> >> If firmware wants any driver to handle a memory range it >> >> can already use E820_RESERVED. The only reason a >> >> new-type was picked in these early implementations was >> >> for experiments around reserving nvdimm memory for driver >> >> use, but also extending it to be covered with struct page >> >> mappings. Outside of that there is no real driving >> >> reason for the new type. >> > >> > But ... if a user is blessed/haunted with such firmware, >> > why not let new types fall back to 'reserved', which is a >> > reasonable default that still allows sufficiently aware >> > Linux drivers to work, right? >> >> True. >> >> > >> >> > So is there any practical reason to mark the memory >> >> > resource as busy in that case, instead of just adding >> >> > it to the reserved list by default and allowing >> >> > properly informed drivers to (exclusively) request it? >> >> >> >> I'm not sure we want firmware to repeat this confusion >> >> going forward. Why support new memory types unless >> >> defined by ACPI or otherwise sufficiently described by >> >> E820_RESERVED? >> > >> > Because it would make the kernel more functional? We should >> > always err on the side of allowing more functionality and >> > not erect roadblocks. >> > >> >> I'm not convinced Linux is better off enabling one-off >> BIOS implementations to pick non-standard numbers. Would >> it not be safer to at least confirm with the user via a >> configuration option, "do you want drivers to access >> unknown memory types"? > > Well, we could emit a warning (or taint the kernel), to > keep the user informed that there's a version mismatch > between kernel and firmware - but otherwise still allow > informed drivers to register that region?
Sounds good to me. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/