3  * Debug and Guest Debug support
29  * For some debug operations we need to tweak some guest registers. As
33  * Guest access to MDSCR_EL1 is trapped by the hypervisor and handled
37  * guest entry. Preserve PSTATE.SS so we can restore the original value
100 	 * to disable guest access to the profiling and trace buffers  in kvm_arm_setup_mdcr_el2()
117 	 *  - Userspace is using the hardware to debug the guest  in kvm_arm_setup_mdcr_el2()
119 	 *  - The guest is not using debug (DEBUG_DIRTY clear).  in kvm_arm_setup_mdcr_el2()
120 	 *  - The guest has enabled the OS Lock (debug exceptions are blocked).  in kvm_arm_setup_mdcr_el2()
162  * Additionally, KVM only traps guest accesses to the debug registers if
163  * the guest is not actively using them (see the DEBUG_DIRTY
164  * flag on vcpu->arch.iflags).  Since the guest must not interfere
165  * with the hardware state when debugging the guest, we must ensure that
166  * trapping is enabled whenever we are debugging the guest using the
180 		/* Save guest debug state */  in kvm_arm_setup_debug()
188 		 * the guest's MDSCR_EL1.SS and PSTATE.SS. Once the  in kvm_arm_setup_debug()
192 		 * If the guest attempts to single step its userspace  in kvm_arm_setup_debug()
194 		 * while in the guest kernel. Because this would be  in kvm_arm_setup_debug()
195 		 * hard to unwind we suppress the guest's ability to  in kvm_arm_setup_debug()
198 		 * This confuses guest debuggers which use  in kvm_arm_setup_debug()
205 			 * If the software step state at the last guest exit  in kvm_arm_setup_debug()
254 		 * enabled. If the guest has enabled the OS Lock, constrain its  in kvm_arm_setup_debug()
255 		 * effects to the guest. Emulate the behavior by clearing  in kvm_arm_setup_debug()
257 		 * exceptions are unaffected by guest configuration of the OS  in kvm_arm_setup_debug()
286 	 * Restore the guest's debug registers if we were using them.  in kvm_arm_clear_debug()
302 		 * debug_ptr to the guest debug state.  in kvm_arm_clear_debug()