Commit 0e8a0996 authored Oct 03, 2014 by Nadav Amit Committed by Paolo Bonzini Nov 03, 2014

KVM: x86: Clear DR7.LE during task-switch

DR7.LE should be cleared during task-switch. This feature is poorly documented.
For reference, see:
http://pdos.csail.mit.edu/6.828/2005/readings/i386/s12_02.htm



SDM [17.2.4]:
  This feature is not supported in the P6 family processors, later IA-32
  processors, and Intel 64 processors.

AMD [2:13.1.1.4]:
  This bit is ignored by implementations of the AMD64 architecture.

Intel's formulation could mean that it isn't even zeroed, but current
hardware indeed does not behave like that.

Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Reviewed-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

parent 518547b3

arch/x86/kvm/vmx.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -5490,7 +5490,7 @@ static int handle_task_switch(struct kvm_vcpu *vcpu)
		}

		/* clear all local breakpoint enable flags */
		vmcs_writel(GUEST_DR7, vmcs_readl(GUEST_DR7) & ~0x55);
		vmcs_writel(GUEST_DR7, vmcs_readl(GUEST_DR7) & ~0x155);

		/*
		* TODO: What about debug traps on tss switch?