Xiao Guangrong [off-list ref] wrote:

On 02/19/2016 06:56 PM, Paolo Bonzini wrote:

quoted

Sometimes when setting a breakpoint a process doesn't stop on it.
This is because the debug registers are not loaded correctly on
VCPU load.

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 4244c2baf57d..f4891f2ece23 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c

@@ -2752,6 +2752,7 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 	}

 	kvm_make_request(KVM_REQ_STEAL_UPDATE, vcpu);
+	vcpu->arch.switch_db_regs |= KVM_DEBUGREG_RELOAD;

Er, i do not understand how it works. The BP is enabled in this test case so
the debug registers are always reloaded before entering guest as
KVM_DEBUGREG_BP_ENABLED bit is always set on switch_db_regs. What did i miss?

Note that KVM_DEBUGREG_BP_ENABLED does not have to be set, since
kvm_update_dr7() is not called once the guest has KVM_DEBUGREG_WONT_EXIT.

Nadav