Add test to check MPRV/MPP behaviour when executing an MRET

test/sim/sw_testcases/mret_mpp_mprv.c

@@ -0,0 +1,111 @@
+#include "tb_cxxrtl_io.h"
+#include "hazard3_csr.h"
+#include "pmp.h"
+
+// Check MPRV is cleared when returning to U mode, but not when returning to M
+// mode. Check that mret clears MPP, no matter which mode is returned to.
+
+/*EXPECTED-OUTPUT***************************************************************
+
+Enabling MPRV, with MPP=M
+mret to M, check MPRV
+mstatus   = 00020080  // mprv=1 mpp=U mpie=1
+mret to M, check MPP affects load/store
+mcause    = 7         // store fault
+mstatus   = 00021880  // mprv=1 mpp=M mpie=1
+mem[mepc] = c108
+mret to U, check MPRV
+mcause    = 1         // instr access fault
+mstatus   = 00000080  // mprv=0 mpp=U mpie=1
+mem[mepc] = 0001      // c.nop
+
+*******************************************************************************/
+
+volatile uint32_t scratch_word;
+
+#define MPRV (1u << 17)
+#define MPP (3u << 11)
+
+extern void handle_exception();
+
+int main() {
+	// Leave PMP in default state (no U permissions).
+	scratch_word = 0;
+
+	tb_puts("Enabling MPRV, with MPP=M\n");
+	set_csr(mstatus, MPP | MPRV);
+
+	// Check that mret to M does not clear MPRV (also, opportunistically,
+	// check that mret to M clears MPP)
+	tb_puts("mret to M, check MPRV\n");
+	write_csr(mtvec, (uintptr_t)&handle_exception);
+	uint32_t mstatus_check;
+	asm volatile (
+		"la %0, 1f\n"
+		"csrw mepc, %0\n"
+		"mret\n"
+		".p2align 2\n"
+		"1:\n"
+		// Note MPP is cleared by the MRET, so must be re-set immediately so
+		// we can do load/stores again. We read out the current mstatus value
+		// at the same time we modify it.
+		"li %0, 0x1800\n"
+		"csrrs %0, mstatus, %0\n"
+		: "+r" (mstatus_check)
+	);
+	// MPP should be U. MPRV should still be set.
+	tb_printf("mstatus   = %08x\n", mstatus_check);
+	// The actual value of MPP is now M again, since we fixed it up.
+
+	// Check that clearing of MPP upon mret immediately affects the
+	// MPRV-modified load/store privilege level.
+	tb_puts("mret to M, check MPP affects load/store\n");
+	write_csr(mcause, 0);
+	asm (
+		"la a0, 1f\n"
+		"csrw mepc, a0\n"
+		"la a0, 2f\n"
+		"csrw mtvec, a0\n"
+		"la a0, scratch_word\n"
+		"mret\n"
+		".p2align 2\n"
+		"1:\n"
+		// We just executed a return from M mode to M mode, but our MPP was
+		// cleared in the process, and our MPRV should still be set.
+		// Therefore our effective load/store privilege is U:
+		"c.sw a0, (a0)\n"
+		// Catch the trap we just caused, and restore MPP to M.
+		".p2align 2\n"
+		"2:\n"
+		"li a0, 0x1800\n"
+		"csrs mstatus, a0\n"
+		: : : "a0"
+	);
+	tb_printf("mcause    = %u\n", read_csr(mcause));
+	tb_printf("mstatus   = %08x\n", read_csr(mstatus));
+	tb_printf("mem[mepc] = %04x\n", *(uint16_t*)read_csr(mepc));
+
+	// Check that mret to U (followed by trapping back to M, as we can't
+	// actually check MPRV from U) *does* clear MPRV
+	tb_puts("mret to U, check MPRV\n");
+	asm (
+		"la a0, 1f\n"
+		"csrw mepc, a0\n"
+		"csrw mtvec, a0\n"
+		"li a0, 0x1800\n"
+		"csrc mstatus, a0\n"
+		"mret\n"
+		".p2align 2\n"
+		// We execute this address twice, first in U-mode then in M-mode:
+		"1:\n"
+		"c.nop\n"
+		: : : "a0"
+	);
+	tb_printf("mcause    = %u\n", read_csr(mcause));
+	tb_printf("mstatus   = %08x\n", read_csr(mstatus));
+	tb_printf("mem[mepc] = %04x\n", *(uint16_t*)read_csr(mepc));
+	tb_assert(read_csr(mepc) == read_csr(mtvec), "Should trap to same address that trapped\n");
+
+
+	return 0;
+}

test/sim/sw_testcases/pmp_mprv.c

@@ -3,24 +3,21 @@
 #include "pmp.h"
 
 // Check that PMP enforces U-mode read/write permissions in M-mode, if both
-// MPRV=1 and MPP=U. Check that this does not affect execute permissions.
-// Check MPRV is cleared when returning to U mode.
-
-#define MCAUSE_LOAD_FAULT 5
-#define MCAUSE_STORE_FAULT 7
-#define MCAUSE_ECALL_UMODE 8
+// MPRV=1 and MPP=U.
+//
+// Check that this does not affect execute permissions.
 
 /*EXPECTED-OUTPUT***************************************************************
 
 Enabling MPRV, with MPP=M
 Set MPP=U, then read memory
-mcause    = 5                   // load fault
-mstatus   = 00021800            // MPRV = 1 MPP = M
-mem[mepc] = 4108                // c.lw a0, (a0)
+mcause    = 5         // load fault
+mstatus   = 00021800  // mprv=1 mpp=M
+mem[mepc] = 4108      // c.lw
 Set MPP=U, then write memory
-mcause    = 7                   // store fault
-mstatus   = 00021800            // MPRV = 1 MPP = M
-mem[mepc] = c108                // c.sw a0, (a0)
+mcause    = 7         // store fault
+mstatus   = 00021800  // mprv=1 mpp=M
+mem[mepc] = c108      // c.sw
 
 *******************************************************************************/
 
@@ -30,11 +27,7 @@ volatile uint32_t scratch_word;
 #define MPP (3u << 11)
 
 int main() {
-	// Give U-mode RW permissions on testbench IO *only* (so any address >=
-	// 0x800 megabytes). This means we can always print and exit the test.
-	write_pmpcfg(0, PMPCFG_A_NAPOT << PMPCFG_A_LSB | PMPCFG_R_BITS | PMPCFG_W_BITS);
-	write_pmpaddr(0, (0x80000000u | 0x3fffffffu) >> 2);
-
+	// Leave PMP in default state (no U permissions).
 	scratch_word = 0;
 
 	tb_puts("Enabling MPRV, with MPP=M\n");
@@ -52,7 +45,7 @@ int main() {
 		"la a0, 1f\n"
 		"csrw mtvec, a0\n"
 		"la a0, scratch_word\n"
-		"la a1, 0x1800\n"
+		"li a1, 0x1800\n"
 
 		// Note the nop is to check that we have not lost X permissions. The
 		// trap should come from the lw.
@@ -76,7 +69,7 @@ int main() {
 		"la a0, 1f\n"
 		"csrw mtvec, a0\n"
 		"la a0, scratch_word\n"
-		"la a1, 0x1800\n"
+		"li a1, 0x1800\n"
 
 		"csrc mstatus, a1\n"
 		"nop\n"