[PATCH Zisslpcfi 2/2] lib: sbi: zsslpcfi detection and elp cfi state reflect back in status

[Deepak Gupta <debug@rivosinc.com>]

This patch adds support for zsslpcfi detection in sbi_hart.c
If zsslpcfi is detected, this turns on menvcfg.CFI

zsslpcfi records status of cfi state in xstatus csr. Missing landing pad
sets MPELP in mstatus. When SBI is redirecting back to S/VS/HS, SPELP is
set in sstatus/vsstatus.

Signed-off-by: Deepak Gupta <debug@rivosinc.com>
---
 include/sbi/riscv_encoding.h |  2 ++
 lib/sbi/sbi_hart.c           | 21 +++++++++++++++++++++
 lib/sbi/sbi_trap.c           | 18 ++++++++++++++++++
 3 files changed, 41 insertions(+)

diff --git a/include/sbi/riscv_encoding.h b/include/sbi/riscv_encoding.h
index 1fb520f..d7886e7 100644
--- a/include/sbi/riscv_encoding.h
+++ b/include/sbi/riscv_encoding.h
@@ -32,6 +32,8 @@
 #define MSTATUS_TVM			_UL(0x00100000)
 #define MSTATUS_TW			_UL(0x00200000)
 #define MSTATUS_TSR			_UL(0x00400000)
+#define MSTATUS_SPELP     		_UL(0x10000000)
+#define MSTATUS_MPELP     		_UL(0x20000000)
 #define MSTATUS32_SD			_UL(0x80000000)
 #if __riscv_xlen == 64
 #define MSTATUS_UXL			_ULL(0x0000000300000000)
diff --git a/lib/sbi/sbi_hart.c b/lib/sbi/sbi_hart.c
index 5447c52..6beae2d 100644
--- a/lib/sbi/sbi_hart.c
+++ b/lib/sbi/sbi_hart.c
@@ -157,6 +157,16 @@ static void mstatus_init(struct sbi_scratch *scratch)
 #endif
 		}
 
+		if (sbi_hart_has_extension(scratch, SBI_HART_EXT_SSLPCFI)) {
+#if __riscv_xlen == 32
+			unsigned long menvcfgh_val;
+			menvcfgh_val = csr_read(CSR_MENVCFGH);
+			menvcfgh_val |= ENVCFGH_CFI;
+			csr_write(CSR_MENVCFGH, menvcfgh_val);
+#else
+			menvcfg_val |= ENVCFG_CFI;
+#endif
+		}
 		csr_write(CSR_MENVCFG, menvcfg_val);
 	}
 
@@ -555,6 +565,7 @@ static int hart_detect_features(struct sbi_scratch *scratch)
 		sbi_scratch_offset_ptr(scratch, hart_features_offset);
 	unsigned long val, oldval;
 	int rc;
+	int ssp_exist, lplr_exist;
 
 	/* If hart features already detected then do nothing */
 	if (hfeatures->detected)
@@ -693,6 +704,16 @@ __mhpm_skip:
 					SBI_HART_EXT_SMSTATEEN, true);
 	}
 
+	if (hfeatures->priv_version >= SBI_HART_PRIV_VER_1_12) {
+		val = csr_read_allowed(CSR_SSP, (unsigned long)&trap);
+		ssp_exist = trap.cause?0:1;
+		val = csr_read_allowed(CSR_LPLR, (unsigned long)&trap);
+		lplr_exist = trap.cause?0:1;
+		if (lplr_exist & ssp_exist)
+			__sbi_hart_update_extension(hfeatures,
+					SBI_HART_EXT_SSLPCFI, true);
+	}
+
 	/* Let platform populate extensions */
 	rc = sbi_platform_extensions_init(sbi_platform_thishart_ptr(),
 					  hfeatures);
diff --git a/lib/sbi/sbi_trap.c b/lib/sbi/sbi_trap.c
index c875c90..a700041 100644
--- a/lib/sbi/sbi_trap.c
+++ b/lib/sbi/sbi_trap.c
@@ -87,6 +87,7 @@ int sbi_trap_redirect(struct sbi_trap_regs *regs,
 		      struct sbi_trap_info *trap)
 {
 	ulong hstatus, vsstatus, prev_mode;
+	bool elp = FALSE;
 #if __riscv_xlen == 32
 	bool prev_virt = (regs->mstatusH & MSTATUSH_MPV) ? TRUE : FALSE;
 #else
@@ -100,6 +101,13 @@ int sbi_trap_redirect(struct sbi_trap_regs *regs,
 	if (prev_mode != PRV_S && prev_mode != PRV_U)
 		return SBI_ENOTSUPP;
 
+	/* If extension has support for CFI, clear MPELP because redirecting to VS or (H)S */
+	if (sbi_hart_has_extension(sbi_scratch_thishart_ptr(), SBI_HART_EXT_SSLPCFI)) {
+		elp = (regs->mstatus & MSTATUS_MPELP)? TRUE: FALSE;
+		/* Since redirecting, clear mpelp unconditionally */
+		regs->mstatus &= ~MSTATUS_MPELP;
+	}
+
 	/* If exceptions came from VS/VU-mode, redirect to VS-mode if
 	 * delegated in hedeleg
 	 */
@@ -153,6 +161,11 @@ int sbi_trap_redirect(struct sbi_trap_regs *regs,
 		/* Get VS-mode SSTATUS CSR */
 		vsstatus = csr_read(CSR_VSSTATUS);
 
+		/*if elp was set, set it back in vsstatus */
+		if (elp) {
+			vsstatus |= MSTATUS_SPELP;
+		}
+
 		/* Set SPP for VS-mode */
 		vsstatus &= ~SSTATUS_SPP;
 		if (prev_mode == PRV_S)
@@ -193,6 +206,11 @@ int sbi_trap_redirect(struct sbi_trap_regs *regs,
 
 		/* Clear SIE for S-mode */
 		regs->mstatus &= ~MSTATUS_SIE;
+
+		/* if elp was set, set it back in mstatus */
+		if (elp) {
+			regs->mstatus |= MSTATUS_SPELP;
+		}
 	}
 
 	return 0;
-- 
2.25.1