KVM: arm64: selftests: Add a test case for a linked breakpoint

Currently, the debug-exceptions test doesn't have a test case for
a linked breakpoint. Add a test case for the linked breakpoint to
the test. The new test case uses a pair of breakpoints. One is the
higiest numbered context-aware breakpoint (for Context ID match),
and the other one is the breakpoint#0 (for Address Match), which
is linked to the context-aware breakpoint.
Signed-off-by: Reiji Watanabe <reijiw@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20221020054202.2119018-8-reijiw@google.com

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

@@ -12,6 +12,10 @@
 #define DBGBCR_EXEC	(0x0 << 3)
 #define DBGBCR_EL1	(0x1 << 1)
 #define DBGBCR_E	(0x1 << 0)
+#define DBGBCR_LBN_SHIFT	16
+#define DBGBCR_BT_SHIFT		20
+#define DBGBCR_BT_ADDR_LINK_CTX	(0x1 << DBGBCR_BT_SHIFT)
+#define DBGBCR_BT_CTX_LINK	(0x3 << DBGBCR_BT_SHIFT)
 
 #define DBGWCR_LEN8	(0xff << 5)
 #define DBGWCR_RD	(0x1 << 3)
@@ -22,7 +26,7 @@
 #define SPSR_D		(1 << 9)
 #define SPSR_SS		(1 << 21)
 
-extern unsigned char sw_bp, sw_bp2, hw_bp, hw_bp2, bp_svc, bp_brk, hw_wp, ss_start;
+extern unsigned char sw_bp, sw_bp2, hw_bp, hw_bp2, bp_svc, bp_brk, hw_wp, ss_start, hw_bp_ctx;
 extern unsigned char iter_ss_begin, iter_ss_end;
 static volatile uint64_t sw_bp_addr, hw_bp_addr;
 static volatile uint64_t wp_addr, wp_data_addr;
@@ -105,6 +109,7 @@ static void reset_debug_state(void)
 	isb();
 
 	write_sysreg(0, mdscr_el1);
+	write_sysreg(0, contextidr_el1);
 
 	/* Reset all bcr/bvr/wcr/wvr registers */
 	dfr0 = read_sysreg(id_aa64dfr0_el1);
@@ -166,6 +171,31 @@ static void install_hw_bp(uint8_t bpn, uint64_t addr)
 	enable_monitor_debug_exceptions();
 }
 
+void install_hw_bp_ctx(uint8_t addr_bp, uint8_t ctx_bp, uint64_t addr,
+		       uint64_t ctx)
+{
+	uint32_t addr_bcr, ctx_bcr;
+
+	/* Setup a context-aware breakpoint for Linked Context ID Match */
+	ctx_bcr = DBGBCR_LEN8 | DBGBCR_EXEC | DBGBCR_EL1 | DBGBCR_E |
+		  DBGBCR_BT_CTX_LINK;
+	write_dbgbcr(ctx_bp, ctx_bcr);
+	write_dbgbvr(ctx_bp, ctx);
+
+	/*
+	 * Setup a normal breakpoint for Linked Address Match, and link it
+	 * to the context-aware breakpoint.
+	 */
+	addr_bcr = DBGBCR_LEN8 | DBGBCR_EXEC | DBGBCR_EL1 | DBGBCR_E |
+		   DBGBCR_BT_ADDR_LINK_CTX |
+		   ((uint32_t)ctx_bp << DBGBCR_LBN_SHIFT);
+	write_dbgbcr(addr_bp, addr_bcr);
+	write_dbgbvr(addr_bp, addr);
+	isb();
+
+	enable_monitor_debug_exceptions();
+}
+
 static void install_ss(void)
 {
 	uint32_t mdscr;
@@ -179,8 +209,10 @@ static void install_ss(void)
 
 static volatile char write_data;
 
-static void guest_code(uint8_t bpn, uint8_t wpn)
+static void guest_code(uint8_t bpn, uint8_t wpn, uint8_t ctx_bpn)
 {
+	uint64_t ctx = 0xabcdef;	/* a random context number */
+
 	/* Software-breakpoint */
 	reset_debug_state();
 	asm volatile("sw_bp: brk #0");
@@ -263,6 +295,17 @@ static void guest_code(uint8_t bpn, uint8_t wpn)
 		     : : : "x0");
 	GUEST_ASSERT_EQ(ss_addr[0], 0);
 
+	/* Linked hardware-breakpoint */
+	hw_bp_addr = 0;
+	reset_debug_state();
+	install_hw_bp_ctx(bpn, ctx_bpn, PC(hw_bp_ctx), ctx);
+	/* Set context id */
+	write_sysreg(ctx, contextidr_el1);
+	isb();
+	asm volatile("hw_bp_ctx: nop");
+	write_sysreg(0, contextidr_el1);
+	GUEST_ASSERT_EQ(hw_bp_addr, PC(hw_bp_ctx));
+
 	GUEST_DONE();
 }
 
@@ -342,11 +385,12 @@ static int debug_version(uint64_t id_aa64dfr0)
 	return FIELD_GET(ARM64_FEATURE_MASK(ID_AA64DFR0_DEBUGVER), id_aa64dfr0);
 }
 
-static void test_guest_debug_exceptions(void)
+static void test_guest_debug_exceptions(uint64_t aa64dfr0)
 {
 	struct kvm_vcpu *vcpu;
 	struct kvm_vm *vm;
 	struct ucall uc;
+	uint8_t brp_num;
 
 	vm = vm_create_with_one_vcpu(&vcpu, guest_code);
 	ucall_init(vm, NULL);
@@ -365,8 +409,15 @@ static void test_guest_debug_exceptions(void)
 	vm_install_sync_handler(vm, VECTOR_SYNC_CURRENT,
 				ESR_EC_SVC64, guest_svc_handler);
 
-	/* Run tests with breakpoint#0 and watchpoint#0. */
-	vcpu_args_set(vcpu, 2, 0, 0);
+	/* Number of breakpoints */
+	brp_num = FIELD_GET(ARM64_FEATURE_MASK(ID_AA64DFR0_BRPS), aa64dfr0) + 1;
+	__TEST_REQUIRE(brp_num >= 2, "At least two breakpoints are required");
+
+	/*
+	 * Run tests with breakpoint#0, watchpoint#0, and the higiest
+	 * numbered (context-aware) breakpoint.
+	 */
+	vcpu_args_set(vcpu, 3, 0, 0, brp_num - 1);
 
 	vcpu_run(vcpu);
 	switch (get_ucall(vcpu, &uc)) {
@@ -483,7 +534,7 @@ int main(int argc, char *argv[])
 		}
 	}
 
-	test_guest_debug_exceptions();
+	test_guest_debug_exceptions(aa64dfr0);
 	test_single_step_from_userspace(ss_iteration);
 
 	return 0;