Messages in this thread Patch in this message | | | Subject | Re: [PATCH 5/7] Use %gs for per-cpu sections in kernel | From | Rusty Russell <> | Date | Mon, 25 Sep 2006 16:03:52 +1000 |
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On Sun, 2006-09-24 at 22:25 -0700, Jeremy Fitzhardinge wrote: > The %gs:per_cpu__foo addressing mode still calculates > 0xbcef00+0xc0433800, which is still a subtraction. My essential point > is that *all* kernel addresses (=kernel symbols) are negative, so using > them as an offset from a segment base (any segment base) is a > subtraction, which requires a 4G limit.
I don't think so. There's *never* address subtraction, there's sometimes 32 bit wrap (glibc uses this to effect subtraction, sure). But there's no wrap here.
To test, I changed the following:
--- smpboot.c.~8~ 2006-09-25 15:51:50.000000000 +1000 +++ smpboot.c 2006-09-25 16:00:36.000000000 +1000 @@ -926,8 +926,9 @@ unsigned long per_cpu_off) { unsigned limit, flags; + extern char __per_cpu_end[]; - limit = (1 << 20); + limit = PAGE_ALIGN((long)__per_cpu_end) >> PAGE_SHIFT; flags = 0x8; /* 4k granularity */ /* present read-write data segment */
Works fine...
Hope that clarifies! Rusty. -- Help! Save Australia from the worst of the DMCA: http://linux.org.au/law
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