linux-kernel - [PATCH] RISC-V: KVM: Prevent HGATP_MODE

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Message-Id: <20250819004643.1884149-1-guoren@kernel.org>
Date: Mon, 18 Aug 2025 20:46:43 -0400
From: guoren@...nel.org
To: guoren@...nel.org,
	paul.walmsley@...ive.com,
	anup@...infault.org,
	atish.patra@...ux.dev,
	fangyu.yu@...ux.alibaba.com
Cc: linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org,
	kvm-riscv@...ts.infradead.org
Subject: [PATCH] RISC-V: KVM: Prevent HGATP_MODE_BARE passed

From: "Guo Ren (Alibaba DAMO Academy)" <guoren@...nel.org>

urrent kvm_riscv_gstage_mode_detect() assumes H-extension must
have HGATP_MODE_SV39X4/SV32X4 at least, but the spec allows
H-extension with HGATP_MODE_BARE alone. The KVM depends on
!HGATP_MODE_BARE at least, so enhance the gstage-mode-detect
to block HGATP_MODE_BARE.

Move gstage-mode-check closer to gstage-mode-detect to prevent
unnecessary init.

Signed-off-by: Guo Ren (Alibaba DAMO Academy) <guoren@...nel.org>
---
 arch/riscv/kvm/gstage.c | 27 ++++++++++++++++++++++++---
 arch/riscv/kvm/main.c   | 35 +++++++++++++++++------------------
 2 files changed, 41 insertions(+), 21 deletions(-)

diff --git a/arch/riscv/kvm/gstage.c b/arch/riscv/kvm/gstage.c
index 24c270d6d0e2..b67d60d722c2 100644
--- a/arch/riscv/kvm/gstage.c
+++ b/arch/riscv/kvm/gstage.c
@@ -321,7 +321,7 @@ void __init kvm_riscv_gstage_mode_detect(void)
 	if ((csr_read(CSR_HGATP) >> HGATP_MODE_SHIFT) == HGATP_MODE_SV57X4) {
 		kvm_riscv_gstage_mode = HGATP_MODE_SV57X4;
 		kvm_riscv_gstage_pgd_levels = 5;
-		goto skip_sv48x4_test;
+		goto done;
 	}
 
 	/* Try Sv48x4 G-stage mode */
@@ -329,10 +329,31 @@ void __init kvm_riscv_gstage_mode_detect(void)
 	if ((csr_read(CSR_HGATP) >> HGATP_MODE_SHIFT) == HGATP_MODE_SV48X4) {
 		kvm_riscv_gstage_mode = HGATP_MODE_SV48X4;
 		kvm_riscv_gstage_pgd_levels = 4;
+		goto done;
 	}
-skip_sv48x4_test:
 
+	/* Try Sv39x4 G-stage mode */
+	csr_write(CSR_HGATP, HGATP_MODE_SV39X4 << HGATP_MODE_SHIFT);
+	if ((csr_read(CSR_HGATP) >> HGATP_MODE_SHIFT) == HGATP_MODE_SV39X4) {
+		kvm_riscv_gstage_mode = HGATP_MODE_SV39X4;
+		kvm_riscv_gstage_pgd_levels = 3;
+		goto done;
+	}
+#else /* CONFIG_32BIT */
+	/* Try Sv32x4 G-stage mode */
+	csr_write(CSR_HGATP, HGATP_MODE_SV32X4 << HGATP_MODE_SHIFT);
+	if ((csr_read(CSR_HGATP) >> HGATP_MODE_SHIFT) == HGATP_MODE_SV32X4) {
+		kvm_riscv_gstage_mode = HGATP_MODE_SV32X4;
+		kvm_riscv_gstage_pgd_levels = 2;
+		goto done;
+	}
+#endif
+
+	/* KVM depends on !HGATP_MODE_OFF */
+	kvm_riscv_gstage_mode = HGATP_MODE_OFF;
+	kvm_riscv_gstage_pgd_levels = 0;
+
+done:
 	csr_write(CSR_HGATP, 0);
 	kvm_riscv_local_hfence_gvma_all();
-#endif
 }
diff --git a/arch/riscv/kvm/main.c b/arch/riscv/kvm/main.c
index 67c876de74ef..8ee7aaa74ddc 100644
--- a/arch/riscv/kvm/main.c
+++ b/arch/riscv/kvm/main.c
@@ -93,6 +93,23 @@ static int __init riscv_kvm_init(void)
 		return rc;
 
 	kvm_riscv_gstage_mode_detect();
+	switch (kvm_riscv_gstage_mode) {
+	case HGATP_MODE_SV32X4:
+		str = "Sv32x4";
+		break;
+	case HGATP_MODE_SV39X4:
+		str = "Sv39x4";
+		break;
+	case HGATP_MODE_SV48X4:
+		str = "Sv48x4";
+		break;
+	case HGATP_MODE_SV57X4:
+		str = "Sv57x4";
+		break;
+	default:
+		return -ENODEV;
+	}
+	kvm_info("using %s G-stage page table format\n", str);
 
 	kvm_riscv_gstage_vmid_detect();
 
@@ -135,24 +152,6 @@ static int __init riscv_kvm_init(void)
 			 (rc) ? slist : "no features");
 	}
 
-	switch (kvm_riscv_gstage_mode) {
-	case HGATP_MODE_SV32X4:
-		str = "Sv32x4";
-		break;
-	case HGATP_MODE_SV39X4:
-		str = "Sv39x4";
-		break;
-	case HGATP_MODE_SV48X4:
-		str = "Sv48x4";
-		break;
-	case HGATP_MODE_SV57X4:
-		str = "Sv57x4";
-		break;
-	default:
-		return -ENODEV;
-	}
-	kvm_info("using %s G-stage page table format\n", str);
-
 	kvm_info("VMID %ld bits available\n", kvm_riscv_gstage_vmid_bits());
 
 	if (kvm_riscv_aia_available())
-- 
2.40.1