linux-kernel - [PATCH] RISC-V: KVM: Allow to downgrade HGATP mode via SATP mode

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Message-Id: <20251122075023.27589-1-fangyu.yu@linux.alibaba.com>
Date: Sat, 22 Nov 2025 15:50:23 +0800
From: fangyu.yu@...ux.alibaba.com
To: anup@...infault.org,
	atish.patra@...ux.dev,
	pjw@...nel.org,
	palmer@...belt.com,
	aou@...s.berkeley.edu,
	alex@...ti.fr
Cc: guoren@...nel.org,
	ajones@...tanamicro.com,
	kvm@...r.kernel.org,
	kvm-riscv@...ts.infradead.org,
	linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Fangyu Yu <fangyu.yu@...ux.alibaba.com>
Subject: [PATCH] RISC-V: KVM: Allow to downgrade HGATP mode via SATP mode

From: Fangyu Yu <fangyu.yu@...ux.alibaba.com>

Currently, HGATP mode uses the maximum value detected by the hardware
but often such a wide GPA is unnecessary, just as a host sometimes
doesn't need sv57.
It's likely that no additional parameters (like no5lvl and no4lvl) are
needed, aligning HGATP mode to SATP mode should meet the requirements
of most scenarios.

Signed-off-by: Fangyu Yu <fangyu.yu@...ux.alibaba.com>
---
 arch/riscv/kvm/gstage.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/kvm/gstage.c b/arch/riscv/kvm/gstage.c
index b67d60d722c2..bff80c80ead3 100644
--- a/arch/riscv/kvm/gstage.c
+++ b/arch/riscv/kvm/gstage.c
@@ -320,7 +320,6 @@ void __init kvm_riscv_gstage_mode_detect(void)
 	csr_write(CSR_HGATP, HGATP_MODE_SV57X4 << HGATP_MODE_SHIFT);
 	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 done;
 	}
 
@@ -328,7 +327,6 @@ void __init kvm_riscv_gstage_mode_detect(void)
 	csr_write(CSR_HGATP, HGATP_MODE_SV48X4 << HGATP_MODE_SHIFT);
 	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;
 	}
 
@@ -336,7 +334,6 @@ void __init kvm_riscv_gstage_mode_detect(void)
 	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 */
@@ -354,6 +351,10 @@ void __init kvm_riscv_gstage_mode_detect(void)
 	kvm_riscv_gstage_pgd_levels = 0;
 
 done:
+#ifdef CONFIG_64BIT
+	kvm_riscv_gstage_mode = min(satp_mode >> SATP_MODE_SHIFT, kvm_riscv_gstage_mode);
+	kvm_riscv_gstage_pgd_levels = kvm_riscv_gstage_mode - HGATP_MODE_SV39X4 + 3;
+#endif
 	csr_write(CSR_HGATP, 0);
 	kvm_riscv_local_hfence_gvma_all();
 }
-- 
2.50.1