On Wed, Feb 18, 2015 at 10:53 AM, Ingo Molnar <[email protected]> wrote: > > * Dan Williams <[email protected]> wrote: > >> On Wed, Feb 18, 2015 at 10:30 AM, Ingo Molnar <[email protected]> wrote: >> > >> > * Dan Williams <[email protected]> wrote: >> > >> >> On Tue, Feb 17, 2015 at 12:42 AM, Boaz Harrosh <[email protected]> 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"? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
