[PATCH v3 Zisslpcfi 2/2] lib: sbi: Zisslpcfi detection and elp cfi state reflect back in status

[Deepak Gupta]

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

Zisslpcfi 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 at rivosinc.com>

---
changelog
v1 --> v3:
 - instead of using "int" for lplr_exist/ssp_exist use "bool"
 - use smaller case true/false
 - updates to use correct extension name "zisslpcfi"
---
 lib/sbi/sbi_hart.c | 23 +++++++++++++++++++++++
 lib/sbi/sbi_trap.c | 16 ++++++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/lib/sbi/sbi_hart.c b/lib/sbi/sbi_hart.c
index 5447c52..f7fb524 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_ZISSLPCFI)) {
+#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);
 	}
 
@@ -446,6 +456,8 @@ static inline char *sbi_hart_extension_id2string(int ext)
 	case SBI_HART_EXT_SMSTATEEN:
 		estr = "smstateen";
 		break;
+	case SBI_HART_EXT_ZISSLPCFI:
+		estr = "zisslpcfi";
 	default:
 		break;
 	}
@@ -555,6 +567,7 @@ static int hart_detect_features(struct sbi_scratch *scratch)
 		sbi_scratch_offset_ptr(scratch, hart_features_offset);
 	unsigned long val, oldval;
 	int rc;
+	bool ssp_exist, lplr_exist;
 
 	/* If hart features already detected then do nothing */
 	if (hfeatures->detected)
@@ -693,6 +706,16 @@ __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;
+		val = csr_read_allowed(CSR_LPLR, (unsigned long)&trap);
+		lplr_exist = trap.cause == 0;
+		if (lplr_exist & ssp_exist)
+			__sbi_hart_update_extension(hfeatures,
+					SBI_HART_EXT_ZISSLPCFI, 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..80d9e65 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_ZISSLPCFI)) {
+		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 +161,10 @@ 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 +205,10 @@ 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