Il 27/02/2014 12:25, Jan Kiszka ha scritto:
On 2014-02-26 16:49, Paolo Bonzini wrote:When not running in guest-debug mode (i.e. the guest controls the debug registers, having to take an exit for each DR access is a waste of time. If the guest gets into a state where each context switch causes DR to be saved and restored, this can take away as much as 40% of the execution time from the guest. If the guest is running with vcpu->arch.db == vcpu->arch.eff_db, we can let it write freely to the debug registers and reload them on the next exit. We still need to exit on the first access, so that the KVM_DEBUGREG_WONT_EXIT flag is set in switch_db_regs; after that, further accesses to the debug registers will not cause a vmexit. Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> --- arch/x86/kvm/vmx.c | 31 ++++++++++++++++++++++++++++++- 1 file changed, 30 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index 6e57e1434cf3..71c57ec48d8f 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -2851,7 +2851,7 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf) vmx_capability.ept, vmx_capability.vpid); } - min = 0; + min = VM_EXIT_SAVE_DEBUG_CONTROLS; #ifdef CONFIG_X86_64 min |= VM_EXIT_HOST_ADDR_SPACE_SIZE; #endif @@ -5121,6 +5121,22 @@ static int handle_dr(struct kvm_vcpu *vcpu) } } + if (vcpu->guest_debug == 0) { + u32 cpu_based_vm_exec_control; + + cpu_based_vm_exec_control = vmcs_read32(CPU_BASED_VM_EXEC_CONTROL); + cpu_based_vm_exec_control &= ~CPU_BASED_MOV_DR_EXITING; + vmcs_write32(CPU_BASED_VM_EXEC_CONTROL, cpu_based_vm_exec_control); + + /* + * No more DR vmexits; force a reload of the debug registers + * and reenter on this instruction. The next vmexit will + * retrieve the full state of the debug registers. + */ + vcpu->arch.switch_db_regs |= KVM_DEBUGREG_WONT_EXIT; + return 1; + } + exit_qualification = vmcs_readl(EXIT_QUALIFICATION); dr = exit_qualification & DEBUG_REG_ACCESS_NUM; reg = DEBUG_REG_ACCESS_REG(exit_qualification); @@ -5147,6 +5163,18 @@ static void vmx_set_dr6(struct kvm_vcpu *vcpu, unsigned long val) { } +static u64 vmx_get_dr7(struct kvm_vcpu *vcpu) +{ + /* DRs are being synced back to vcpu->arch, exit on DR access. */ + u32 cpu_based_vm_exec_control; + + cpu_based_vm_exec_control = vmcs_read32(CPU_BASED_VM_EXEC_CONTROL); + cpu_based_vm_exec_control |= CPU_BASED_MOV_DR_EXITING; + vmcs_write32(CPU_BASED_VM_EXEC_CONTROL, cpu_based_vm_exec_control); + + return vmcs_readl(GUEST_DR7); +}The general idea looks ok (It passes x86/debug.flat unit test, right?).
Yes, of course.
But this side effect of get_dr7 seems a bit ugly to me. Also the imbalanced updates of arch.switch_db_regs: KVM_DEBUGREG_WONT_EXIT is set by the vendor code but cleared in a common x86 path.
I can certainly remove the difference in the updates of KVM_DEBUGREG_WONT_EXIT. It made some sense when the constant was called KVM_DEBUGREG_DIRTY but not now that I renamed it.
I don't like the side effect particularly, either, but I don't have any better idea.
Paolo
Can't you make this more regular and explicit? Jan+ static void vmx_set_dr7(struct kvm_vcpu *vcpu, unsigned long val) { vmcs_writel(GUEST_DR7, val); @@ -8606,6 +8634,7 @@ static struct kvm_x86_ops vmx_x86_ops = { .set_gdt = vmx_set_gdt, .get_dr6 = vmx_get_dr6, .set_dr6 = vmx_set_dr6, + .get_dr7 = vmx_get_dr7, .set_dr7 = vmx_set_dr7, .cache_reg = vmx_cache_reg, .get_rflags = vmx_get_rflags,
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