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

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Message-Id: <20250819020133.93545-1-fangyu.yu@linux.alibaba.com>
Date: Tue, 19 Aug 2025 10:01:33 +0800
From: fangyu.yu@...ux.alibaba.com
To: guoren@...nel.org
Cc: anup@...infault.org,
	atish.patra@...ux.dev,
	fangyu.yu@...ux.alibaba.com,
	kvm-riscv@...ts.infradead.org,
	kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-riscv@...ts.infradead.org,
	paul.walmsley@...ive.com
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.

This patch helps to detect hardware function missing in advance,
prevent software from entering incorrect logic.

Reviewed-by: Fangyu Yu <fangyu.yu@...ux.alibaba.com>

>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