allow kprobes to run on top of preempt emulation

allow kprobes to run on top of preempt emulation

[Andrea Arcangeli]

This patch makes preempt emulation more strict in differentiating its
own dr0 hardware breakpoint from a singlestep in return from kprobes
pre-handler that will invoke the post-handler through int1 debug TS on
eflags. This avoids GPF when kprobes returns from pre-handler with the
dr7 loaded with preempt emulation.

Signed-off-by: Andrea Arcangeli <andrea@qumranet.com>

--- kvm-userland/kernel/preempt.c	2008-05-06 19:33:40.000000000 +0200
+++ /home/andrea/kernel/qumranet/kvm/kernel/preempt.c	2008-06-05 00:18:06.000000000 +0200
@@ -140,6 +147,11 @@
      "cmp $0x701, " TMP " \n\t"
      "pop "  TMP " \n\t"
      "jnz .Lnotme \n\t"
+     "push "  TMP " \n\t"
+     "mov %db6, " TMP " \n\t"
+     "test $0x1, " TMP " \n\t"
+     "pop "  TMP " \n\t"
+     "jz .Lnotme \n\t"
      SAVE_REGS "\n\t"
 #ifdef CONFIG_X86_64
      "leaq 120(%rsp),%rdi\n\t"

Re: allow kprobes to run on top of preempt emulation

[Avi Kivity]

Andrea Arcangeli wrote:
> This patch makes preempt emulation more strict in differentiating its
> own dr0 hardware breakpoint from a singlestep in return from kprobes
> pre-handler that will invoke the post-handler through int1 debug TS on
> eflags. This avoids GPF when kprobes returns from pre-handler with the
> dr7 loaded with preempt emulation.
>
>   

Applied, thanks.


-- 
error compiling committee.c: too many arguments to function