Alex Williamson reported that a Windows game does something weird that makes the guest save and restore debug registers on each context switch. This cause several hundred thousands vmexits per second, and basically cuts performance in half when running under KVM. However, when not running in guest-debug mode, the guest controls the debug registers and having to take an exit for each DR access is a waste of time. We just need one vmexit to load any stale values of DR0-DR6, and then we can let the guest run freely. On the next vmexit (whatever the reason) we will read out whatever changes the guest made to the debug registers. On top of this, we can implement SVM support and let nested guests run with dirty debug registers too. Paolo Bonzini (4): KVM: vmx: we do rely on loading DR7 on entry KVM: x86: change vcpu->arch.switch_db_regs to a bit mask KVM: x86: Allow the guest to run with dirty debug registers KVM: vmx: Allow the guest to run with dirty debug registers arch/x86/include/asm/kvm_host.h | 8 ++++++- arch/x86/kvm/vmx.c | 48 +++++++++++++++++++++++++++++++++++++---- arch/x86/kvm/x86.c | 29 +++++++++++++++++++++++-- 3 files changed, 78 insertions(+), 7 deletions(-) -- 1.8.3.1 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
