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

Currently, the debug-exceptions test doesn't have a test case for
a linked watchpoint. Add a test case for the linked watchpoint to
the test. The new test case uses the highest numbered context-aware
breakpoint (for Context ID match), and the watchpoint#0, 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/20221020054202.2119018-9-reijiw@google.com

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

@@ -22,6 +22,9 @@
 #define DBGWCR_WR	(0x2 << 3)
 #define DBGWCR_EL1	(0x1 << 1)
 #define DBGWCR_E	(0x1 << 0)
+#define DBGWCR_LBN_SHIFT	16
+#define DBGWCR_WT_SHIFT		20
+#define DBGWCR_WT_LINK		(0x1 << DBGWCR_WT_SHIFT)
 
 #define SPSR_D		(1 << 9)
 #define SPSR_SS		(1 << 21)
@@ -171,6 +174,28 @@ static void install_hw_bp(uint8_t bpn, uint64_t addr)
 	enable_monitor_debug_exceptions();
 }
 
+static void install_wp_ctx(uint8_t addr_wp, uint8_t ctx_bp, uint64_t addr,
+			   uint64_t ctx)
+{
+	uint32_t wcr;
+	uint64_t 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 linked watchpoint (linked to the context-aware breakpoint) */
+	wcr = DBGWCR_LEN8 | DBGWCR_RD | DBGWCR_WR | DBGWCR_EL1 | DBGWCR_E |
+	      DBGWCR_WT_LINK | ((uint32_t)ctx_bp << DBGWCR_LBN_SHIFT);
+	write_dbgwcr(addr_wp, wcr);
+	write_dbgwvr(addr_wp, addr);
+	isb();
+
+	enable_monitor_debug_exceptions();
+}
+
 void install_hw_bp_ctx(uint8_t addr_bp, uint8_t ctx_bp, uint64_t addr,
 		       uint64_t ctx)
 {
@@ -306,6 +331,16 @@ static void guest_code(uint8_t bpn, uint8_t wpn, uint8_t ctx_bpn)
 	write_sysreg(0, contextidr_el1);
 	GUEST_ASSERT_EQ(hw_bp_addr, PC(hw_bp_ctx));
 
+	/* Linked watchpoint */
+	reset_debug_state();
+	install_wp_ctx(wpn, ctx_bpn, PC(write_data), ctx);
+	/* Set context id */
+	write_sysreg(ctx, contextidr_el1);
+	isb();
+	write_data = 'x';
+	GUEST_ASSERT_EQ(write_data, 'x');
+	GUEST_ASSERT_EQ(wp_data_addr, PC(write_data));
+
 	GUEST_DONE();
 }