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Re: [Xen-devel] [PATCH 2/5] xen/x86-64: clean up warnings aboutIST-usin

To: Jan Beulich <jbeulich@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH 2/5] xen/x86-64: clean up warnings aboutIST-using traps
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Fri, 08 May 2009 08:23:01 -0700
Cc: Ingo Molnar <mingo@xxxxxxx>, the arch/x86 maintainers <x86@xxxxxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>
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Jan Beulich wrote:
else if (addr == (unsigned long)int3)
                addr = (unsigned long)xen_int3;
-       else
-               WARN_ON(val->ist != 0);
+       else if (addr == (unsigned long)double_fault ||
+                addr == (unsigned long)stack_segment) {

I don't think you want to exclude handling stack faults: Ordinary memory
references using rsp or rbp as the base register will cause these instead
of general protection faults when the resulting effective address is non-
canonical.

So even usermode memory accesses? Ew. Well, we can run the trap handler on the normal kernel stack in that case. I'll cook something up.

   J

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