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Date: Mon, 25 Sep 2006 16:03:52 +1000 From: Rusty Russell <rusty@...tcorp.com.au> To: Jeremy Fitzhardinge <jeremy@...p.org> Cc: Andi Kleen <ak@....de>, lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>, virtualization <virtualization@...ts.osdl.org> Subject: Re: [PATCH 5/7] Use %gs for per-cpu sections in kernel 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 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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