Commit b3d93772 authored by Sean Christopherson's avatar Sean Christopherson
Browse files

KVM: arm64: selftests: Disable single-step without relying on ucall() 

Automatically disable single-step when the guest reaches the end of the
verified section instead of using an explicit ucall() to ask userspace to
disable single-step.  An upcoming change to implement a pool-based scheme
for ucall() will add an atomic operation (bit test and set) in the guest
ucall code, and if the compiler generate "old school" atomics, e.g.

  40e57c:       c85f7c20        ldxr    x0, [x1]
  40e580:       aa100011        orr     x17, x0, x16
  40e584:       c80ffc31        stlxr   w15, x17, [x1]
  40e588:       35ffffaf        cbnz    w15, 40e57c <__aarch64_ldset8_sync+0x1c>

the guest will hang as the local exclusive monitor is reset by eret,
i.e. the stlxr will always fail due to the debug exception taken to EL2.

Link: https://lore.kernel.org/all/20221006003409.649993-8-seanjc@google.com


Cc: Oliver Upton <oliver.upton@linux.dev>
Cc: Marc Zyngier <maz@kernel.org>
Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20221117002350.2178351-3-seanjc@google.com


Reviewed-by: default avatarOliver Upton <oliver.upton@linux.dev>
parent 1cec8bbc

tools/testing/selftests/kvm/aarch64/debug-exceptions.c

+15 −13
Original line number Original line Diff line number Diff line
@@ -241,7 +241,6 @@ static void guest_svc_handler(struct ex_regs *regs) 




enum single_step_op {

enum single_step_op {

	SINGLE_STEP_ENABLE = 0,

	SINGLE_STEP_ENABLE = 0,

	SINGLE_STEP_DISABLE = 1,

};

};





static void guest_code_ss(int test_cnt)

static void guest_code_ss(int test_cnt)
@@ -258,7 +257,7 @@ static void guest_code_ss(int test_cnt) 
		GUEST_SYNC(SINGLE_STEP_ENABLE);

		GUEST_SYNC(SINGLE_STEP_ENABLE);





		/*

		/*

		 * The userspace will veriry that the pc is as expected during

		 * The userspace will verify that the pc is as expected during

		 * single step execution between iter_ss_begin and iter_ss_end.

		 * single step execution between iter_ss_begin and iter_ss_end.

		 */

		 */

		asm volatile("iter_ss_begin:nop\n");

		asm volatile("iter_ss_begin:nop\n");
@@ -268,11 +267,9 @@ static void guest_code_ss(int test_cnt) 
		bvr = read_sysreg(dbgbvr0_el1);

		bvr = read_sysreg(dbgbvr0_el1);

		wvr = read_sysreg(dbgwvr0_el1);

		wvr = read_sysreg(dbgwvr0_el1);





		/* Userspace disables Single Step when the end is nigh. */

		asm volatile("iter_ss_end:\n");

		asm volatile("iter_ss_end:\n");





		/* Disable Single Step execution */

		GUEST_SYNC(SINGLE_STEP_DISABLE);



		GUEST_ASSERT(bvr == w_bvr);

		GUEST_ASSERT(bvr == w_bvr);

		GUEST_ASSERT(wvr == w_wvr);

		GUEST_ASSERT(wvr == w_wvr);

	}

	}
@@ -364,15 +361,12 @@ void test_single_step_from_userspace(int test_cnt) 
			TEST_ASSERT(cmd == UCALL_SYNC,

			TEST_ASSERT(cmd == UCALL_SYNC,

				    "Unexpected ucall cmd 0x%lx", cmd);

				    "Unexpected ucall cmd 0x%lx", cmd);





			if (uc.args[1] == SINGLE_STEP_ENABLE) {

			TEST_ASSERT(uc.args[1] == SINGLE_STEP_ENABLE,

				    "Unexpected ucall action 0x%lx", uc.args[1]);



			debug.control = KVM_GUESTDBG_ENABLE |

			debug.control = KVM_GUESTDBG_ENABLE |

					KVM_GUESTDBG_SINGLESTEP;

					KVM_GUESTDBG_SINGLESTEP;

			ss_enable = true;

			ss_enable = true;

			} else {

				debug.control = KVM_GUESTDBG_ENABLE;

				ss_enable = false;

			}



			vcpu_guest_debug_set(vcpu, &debug);

			vcpu_guest_debug_set(vcpu, &debug);

			continue;

			continue;

		}

		}
@@ -385,6 +379,14 @@ void test_single_step_from_userspace(int test_cnt) 
			    "Unexpected pc 0x%lx (expected 0x%lx)",

			    "Unexpected pc 0x%lx (expected 0x%lx)",

			    pc, test_pc);

			    pc, test_pc);





		if ((pc + 4) == (uint64_t)&iter_ss_end) {

			test_pc = 0;

			debug.control = KVM_GUESTDBG_ENABLE;

			ss_enable = false;

			vcpu_guest_debug_set(vcpu, &debug);

			continue;

		}



		/*

		/*

		 * If the current pc is between iter_ss_bgin and

		 * If the current pc is between iter_ss_bgin and

		 * iter_ss_end, the pc for the next KVM_EXIT_DEBUG should

		 * iter_ss_end, the pc for the next KVM_EXIT_DEBUG should