On Thu, 5 Jul 2007, Pavel Machek wrote:
Hi!
On some machines, buggy BIOSes don't properly setup WB MTRRs to
cover all available RAM, meaning the last few megs (or even gigs)
of memory will be marked uncached. Since Linux tends to allocate
from high memory addresses first, this causes the machine to be
unusably slow as soon as the kernel starts really using memory
(i.e. right around init time).
This patch works around the problem by scanning the MTRRs at
boot and figuring out whether the current end_pfn value (setup
by early e820 code) goes beyond the highest WB MTRR range, and
if so, trimming it to match. A fairly obnoxious KERN_WARNING
is printed too, letting the user know that not all of their
memory is available due to a likely BIOS bug.
Something similar could be done on i386 if needed, but the boot
ordering would be slightly different, since the MTRR code on i386
depends on the boot_cpu_data structure being setup.
This patch fixes a bug in the last patch that caused the code to
run on non-Intel machines (AMD machines apparently don't need it
and it's untested on other non-Intel machines, so best keep it
off).
akpm -- this one should replace all the mtrr patches currently
in your tree.
Yinghai, maybe you can test this on one of your AMD machines to
make sure I got the CPU code right?
+ if ((highest_addr >> PAGE_SHIFT) != end_pfn) {
+ printk(KERN_WARNING "***************\n");
+ printk(KERN_WARNING "**** WARNING: likely BIOS bug\n");
+ printk(KERN_WARNING "**** MTRRs don't cover all of "
+ "memory, trimmed %ld pages\n", end_pfn -
+ (highest_addr >> PAGE_SHIFT));
+ printk(KERN_WARNING "***************\n");
+ end_pfn = highest_addr >> PAGE_SHIFT;
I'd say using that many stars for KERN_WARNING printk is sign of
mental illness or something...
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
Will this patch make it into 2.6.23?
Been patching manually for a while with each -rc for 2.6.22..
Justin.
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