Commit 81908bf4 authored by Paolo Bonzini's avatar Paolo Bonzini
Browse files

KVM: vmx: Allow the guest to run with dirty debug registers 



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: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent c77fb5fe

arch/x86/kvm/vmx.c

+37 −1
Original line number Diff line number Diff line
@@ -43,6 +43,7 @@ 
#include <asm/i387.h>

#include <asm/xcr.h>

#include <asm/perf_event.h>

#include <asm/debugreg.h>

#include <asm/kexec.h>



#include "trace.h"
@@ -2850,7 +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
@@ -5084,6 +5085,22 @@ 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);
@@ -5110,6 +5127,24 @@ static void vmx_set_dr6(struct kvm_vcpu *vcpu, unsigned long val) 
{

}



static void vmx_sync_dirty_debug_regs(struct kvm_vcpu *vcpu)

{

	u32 cpu_based_vm_exec_control;



	get_debugreg(vcpu->arch.db[0], 0);

	get_debugreg(vcpu->arch.db[1], 1);

	get_debugreg(vcpu->arch.db[2], 2);

	get_debugreg(vcpu->arch.db[3], 3);

	get_debugreg(vcpu->arch.dr6, 6);

	vcpu->arch.dr7 = vmcs_readl(GUEST_DR7);



	vcpu->arch.switch_db_regs &= ~KVM_DEBUGREG_WONT_EXIT;



	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);

}



static void vmx_set_dr7(struct kvm_vcpu *vcpu, unsigned long val)

{

	vmcs_writel(GUEST_DR7, val);
@@ -8628,6 +8663,7 @@ static struct kvm_x86_ops vmx_x86_ops = { 
	.get_dr6 = vmx_get_dr6,

	.set_dr6 = vmx_set_dr6,

	.set_dr7 = vmx_set_dr7,

	.sync_dirty_debug_regs = vmx_sync_dirty_debug_regs,

	.cache_reg = vmx_cache_reg,

	.get_rflags = vmx_get_rflags,

	.set_rflags = vmx_set_rflags,

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