Messages in this thread | | | Date | Sat, 29 Sep 2012 10:41:47 +0800 | From | Zhenzhong Duan <> | Subject | Re: [RFC] x86: mtrr: Constrain WB MTRR to max phys mem prior to cleanup |
| |
On 2012-09-29 01:37, Peter Hurley wrote: > On Sun, 2012-09-09 at 23:54 -0400, zhenzhong.duan wrote: >> On 2012-09-08 02:40, H. Peter Anvin wrote: >>> On 09/07/2012 10:44 AM, Peter Hurley wrote: >>> >>>> diff --git a/arch/x86/kernel/cpu/mtrr/cleanup.c >>>> b/arch/x86/kernel/cpu/mtrr/cleanup.c >>> I really don't like it as it introduces yet another user of max_pfn, >>> which should be going away. Furthermore, the better question is what >>> remaining needs there are for MTRR cleanup; historically the reason >>> was that it prevented the display from being mapped WC via MTRR due to >>> the MTRR conflict resolution rules favoring UC. >> For a large memory system, mtrr_cleanup offten fail in most case. Even >> if it succeed, it often occupy all of MTRR entrys. >> How was display mapped as WC in above case? > Without this patch, mtrr_cleanup could not optimize. The original MTRR > setup from BIOS remained, which left the display as UC (and a lot of log > spew). Hi, I am confused here. Does HPA means mtrr_cleanup's purpose is to occupy all mtrr entrys and prevent display setting a WC entry in it? As page level will do that in current code? If it is, then mtrr_cleanup could be removed now. > >> Why did bios give a lot of space then real mem, for hotplug? > I assume the reason was for hotplug. > > An interesting side note: more recent revisions of this BIOS (rev. A11) > report one less variable MTRR (so, IA32_MTRRCAP is writable?) From manual, it's readonly, writing it will lead to #GP. > >>> However, the right way to fix that is to use the PAT interfaces, which >>> doesn't have this drawback -- then MTRR cleanup becomes entirely >>> superfluous and the problem goes away. >> Do you mean disable MTRR totally here? > Well, since PAT entries marked WC override all MTRR settings, whatever > the BIOS set the variable MTRRs to becomes irrelevant, so not disabled > but rather ignored. Oh, I see, WC in page level take precedence. Is the fix already in upstream? thanks zduan
| |