Commit 4ba51fd7 authored Apr 03, 2008 by Roland McGrath Committed by Linus Torvalds Apr 03, 2008

x86 ptrace: avoid unnecessary wrmsr



This avoids using wrmsr on MSR_IA32_DEBUGCTLMSR when it's not needed.
No wrmsr ever needs to be done if noone has ever used block stepping.

Without this change, using ptrace on 2.6.25 on an x86 KVM guest
will tickle KVM's missing support for the MSR and crash the guest
kernel.  Though host KVM is the buggy one, this makes for a regression
in the guest behavior from 2.6.24->2.6.25 that we can easily avoid.

I also corrected some bad whitespace.

Signed-off-by: Roland McGrath <roland@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 2eccd6f6

arch/x86/kernel/step.c

+7 −4

Original line number	Diff line number	Diff line
		@@ -140,6 +140,9 @@ static int enable_single_step(struct task_struct *child)
		*/
		static void write_debugctlmsr(struct task_struct *child, unsigned long val)
		{
		if (child->thread.debugctlmsr == val)
		return;

		child->thread.debugctlmsr = val;

		if (child != current)