On Thu, Jun 29, 2006 at 02:51:33PM -0700, Luck, Tony wrote: > > > Also it is wrong to put TLB map of RAM that does not exist together > > > with kernel text and data. > > > > Sorry, I don't understand that. > > Here's an example. Many systems have (for legacy reasons) mapped > VGA memory at 0xA0000-0xC0000. This memory is typically uncacheable > so that when you write to those addresses the bits show up on the > screen (rather than sitting in the processor cache for some indeterminate > amount of time). > > Now if Linux is using a 64MB entry to map the kernel, and the kernel > has been loaded into the bottom 64M of memory, the mapping for the > kernel (which has a WB attribute) will overlap the VGA memory (which > doesn't support WB) ... and so you will most probably machine check > when someone accesses the VGA (or worse if some speculative access or > prefetch happens to pull from the VGA area). > > So the rule is that Linux must never create TLB mappings for things > that don't exist, or for blocks of memory with incompatible attributes. I might be confused, but I'm not exactly sure that my patch would run into this problem. It only tries to insert the "Crash kernel" resource as a sub-resource of an existing "System RAM" resource, and does so in such a way that it should not overlap with any existing sub-resources. Surely VGA and the like are in completely different resources not covered by a "System RAM" resource. -- Horms H: http://www.vergenet.net/~horms/ W: http://www.valinux.co.jp/en/ - : send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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