Mikael Pettersson <[EMAIL PROTECTED]> writes: > Andi Kleen writes: > > On Tuesday 30 August 2005 16:45, Alan Cox wrote: > > > On Llu, 2005-08-29 at 18:20 -0600, Eric W. Biederman wrote: > > > > ways. Currently this code only allows for an additional flavor > > > > of uncached access to physical memory addresses which should be hard > > > > to abuse, and should raise no additional aliasing problems. No > > > > attempt has been made to fix theoretical aliasing problems. > > > > > > Even an uncached/cached alias causes random memory corruption or an MCE > > > on x86 systems. In fact it can occur even for an alias not in theory > > > touched by the CPU if it happens to prefetch into or speculate the > > > address. > > > > > > Also be sure to read the PII Xeon errata - early PAT has a bug or two. > > > > > > We can always force cpu_has_pat == 0 on these machines. > > I don't think it is worth it to add any more complicated workarounds > > for old broken systems. > > I don't have the spec updates in front of me, but I believe the PAT > bug existed well into the P4 line. The workaround is simply to make > the high 4 PAT entries identical to the low 4 entries. (But I confess > to not having a clue as to whether it's still useful then or not.)
It is still useful even if that is the case. Unless we need something more than WC we don't have a need for anything else. If you could track down the reference you are thinking of I would appreciate it. According to the errata I can find simply not using the high 4 entries is sufficient, to avoid the problem. Eric - 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/
