Messages in this thread | | | Date | Tue, 15 Jan 2008 23:17:58 +0100 | From | Ingo Molnar <> | Subject | Re: [patch 02/11] PAT x86: Map only usable memory in x86_64 identity map and kernel text |
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* Siddha, Suresh B <suresh.b.siddha@intel.com> wrote:
> On Mon, Jan 14, 2008 at 05:43:24PM +0100, Ingo Molnar wrote: > > > > * Pallipadi, Venkatesh <venkatesh.pallipadi@intel.com> wrote: > > > > > Also, relying on MTRR, is like giving more importance to BIOS writer > > > than required :-). I think the best way to deal with MTRR is just to > > > not touch it. Leave it as it is and do not try to assume that they are > > > correct, as frequently they will not be. > > > > i'd suggest the following strategy on PAT-capable CPUs: > > > > - do not try to write MTRRs. Ever. > > > > - _read_ the current MTRR settings (including the default MTRR) and > > check them against the e820 map. I can see two basic types of > > mismatches: > > > > - RAM area marked fine in e820 but marked UC by MTRR: this > > currently results in a slow system. > > Time to resurrect Jesse's old patches > i386-trim-memory-not-covered-by-wb-mtrrs.patch(which was in -mm > sometime back)
just to make sure i understood the attribute priorities right: we cannot just mark it WB in the PAT and expect it to be write-back - the UC of the MTRR will control?
> > (NOTE: UC- would be fine and > > overridable by PAT, hence it's not a conflict we should detect.) > > UC- can't be specified by MTRR's.
hm, only by PATs? Not even by the default MTRR?
> > - mmio area marked cacheable in the MTRR (results in broken > > system) > > PAT can help specify the UC/WC attribute here.
ok. So it seems we dont even need all that many special cases, a "dont write MTRRs" and "use PATs everywhere" rule would just do the right thing all across?
Ingo
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