On Thu, Nov 05, 2015 at 11:43:59AM -0800, Luis R. Rodriguez wrote: > On Thu, Nov 5, 2015 at 11:14 AM, Yinghai Lu <[email protected]> wrote: > > On Mon, Sep 14, 2015 at 7:46 AM, Stuart Hayes <[email protected]> > > wrote: > >> > >> Booting with 'disable_mtrr_cleanup' works, but the system I am working with > >> isn't actually failing--it just gets ugly error messages. And the BIOS on > >> the > >> system I am working with had set up the MTRRs correctly. > > > > Please post boot log and /proc/mtrr for: > > 1. without your patch > > 2. without your patch and with disable_mtrr_cleanup in boot command line. > > 3. with your patch. > > Stuart, > > to provide some context -- I reached out to Yinghai as he wrote the > original mtrr cleanup code. The commit logs seem to read that a crash > was possible on systems with > 4 GiB RAM with some types of BIOSes... > The cleanup code seems to trigger when variable MTRRs do not exist > that are UC, or when all varible MTRRs that exist are just UC + WB > (Yinghai correct me if I'm wrong). The commit log in question > (95ffa2438d0e9 "x86: mtrr cleanup for converting continuous to > discrete layout, v8") was not very clear about the cause of the crash > -- but suppose the issue here was the BIOS on some systems might want > to create some UC variable MTRRs early on and there was no UC MTRRs > available, and I can only guess the cleanup exists as hack for those > BIOSes. Even if that was the case -- its still not clear *why* the > crash would happen but I suppose a driver mishap can happen without UC > guarantees for some devices the BIOS may want to enable UC MTRR on. > > To be able to determine what we do upstream we need to understand the > above first. We also need to understand if the cleanup might also be > implicated by userspace drivers using /proc/mtrr, or if a proprietary > driver exists that does use mtrr_add() directly even though PAT has > been available for ages and all drivers are now properly converted. > > With clear answers to the above we'll be able to determine what the > right course of action should be for this patch. For instance I'm > inclined to strive to disable the complex cleanup code if we don't > need it anymore, but if we do need it your patch makes sense. If the > patch makes sense then though are we going to have to keep updating > the segment size *every time* as systems grow? That seems rather > silly. And if PAT is prevalent why are vendors adding MTRRs still? The > cleanup seems complex and a major hack for a fix for some BIOSes, I'd > much rather identify the exact issue and only have a fix to address > that case.
I never heard back... so let's take this up on the other thread I just raised. Luis
