Date: Thu, 8 May 2003 21:52:23 +0200 From: Mark Santcroos <marks@ripe.net> To: "Alan L. Cox" <alc@imimic.com> Cc: freebsd-current@freebsd.org Subject: Re: data corruption with current (maybe sis chipset related?) Message-ID: <20030508195223.GC676@laptop.6bone.nl> In-Reply-To: <3EBAB353.4E5F8440@imimic.com> References: <20030506162410.M66653@daneel.foundation.hs> <20030506171632.GA767@laptop.6bone.nl> <20030508111807.GB1390@laptop.6bone.nl> <20030508155123.G78057@daneel.foundation.hs> <20030508142234.GA1359@laptop.6bone.nl> <3EBAB353.4E5F8440@imimic.com>
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On Thu, May 08, 2003 at 02:43:15PM -0500, Alan L. Cox wrote: > For the record, this is not completely correct. DISABLE_PSE does > control the use of 4MB pages. DISABLE_PG_G is, however, something > entirely different. Normally, on a process context switch TLB entries > for the old address space are flushed. If a TLB entry corresponds to an > in-kernel virtual-to-physical mapping, there is no reason to flush that > entry because all processes share the same kernel address space. > Setting the "G"lobal bit on a page table entry accomplishes this. In > other words, the TLB entry persists across context switches. > DISABLE_PG_G disables this. > > The problem with PG_G is that the "flush all" TLB entries operation, > just like a context switch, has no effect on entries marked as global. > Such entries have to be flushed by specifying their address in a "flush > single page" operation. Sometimes the failure to flush an entry is > covered up by a combination of DISABLE_PG_G and a lucky context switch. > > So, in summary, it does make sense to try these options separately. This is not my expertise, so take me with a grain of salt :) I think Terry also already mentioned this. PSE for the 4M pages and PG_G for the global pages. I also think that last time we concluded that they are both needed. He mentioned I guess that while using only one of them might "solve" the problem, but that would only be hiding the problem for a bit longer. Mark -- Mark Santcroos RIPE Network Coordination Centre http://www.ripe.net/home/mark/ New Projects Group/TTM
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