[PATCH v6 3/4] RISC-V: KVM: Detect and expose supported HGATP G-stage modes

fangyu.yu
2026-03-30T12:26:54Z

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

Extend kvm_riscv_gstage_mode_detect() to probe all HGATP.MODE values
supported by the host and record them in a bitmask. Keep tracking the
maximum supported G-stage page table level for existing internal users.

Also provide lightweight helpers to retrieve the supported-mode bitmask
and validate a requested HGATP.MODE against it.

Signed-off-by: Fangyu Yu <fangyu.yu@linux.alibaba.com>
Reviewed-by: Andrew Jones <andrew.jones@oss.qualcomm.com>
---
arch/riscv/include/asm/kvm_gstage.h | 11 ++++++++
arch/riscv/kvm/gstage.c | 43 +++++++++++++++--------------
2 files changed, 34 insertions(+), 20 deletions(-)

diff --git a/arch/riscv/include/asm/kvm_gstage.h b/arch/riscv/include/asm/kvm_gstage.h
index 70d9d483365e..bbf8f45c6563 100644
--- a/arch/riscv/include/asm/kvm_gstage.h
+++ b/arch/riscv/include/asm/kvm_gstage.h
@@ -31,6 +31,7 @@ struct kvm_gstage_mapping {
#endif

extern unsigned long kvm_riscv_gstage_max_pgd_levels;
+extern u32 kvm_riscv_gstage_supported_mode_mask;

#define kvm_riscv_gstage_pgd_xbits 2
#define kvm_riscv_gstage_pgd_size (1UL << (HGATP_PAGE_SHIFT + kvm_riscv_gstage_pgd_xbits))
@@ -102,4 +103,14 @@ static inline void kvm_riscv_gstage_init(struct kvm_gstage *gstage, struct kvm *
gstage->pgd_levels = kvm->arch.pgd_levels;
}

+static inline u32 kvm_riscv_get_hgatp_mode_mask(void)
+{
+ return kvm_riscv_gstage_supported_mode_mask;
+}
+
+static inline bool kvm_riscv_hgatp_mode_is_valid(unsigned long mode)
+{
+ return kvm_riscv_gstage_supported_mode_mask & BIT(mode);
+}
+
#endif
diff --git a/arch/riscv/kvm/gstage.c b/arch/riscv/kvm/gstage.c
index 7c4c34bc191b..459041255c14 100644
--- a/arch/riscv/kvm/gstage.c
+++ b/arch/riscv/kvm/gstage.c
@@ -16,6 +16,8 @@ unsigned long kvm_riscv_gstage_max_pgd_levels __ro_after_init = 3;
#else
unsigned long kvm_riscv_gstage_max_pgd_levels __ro_after_init = 2;
#endif
+/* Bitmask of supported HGATP.MODE encodings (BIT(HGATP_MODE_*)). */
+u32 kvm_riscv_gstage_supported_mode_mask __ro_after_init;

#define gstage_pte_leaf(__ptep) \
(pte_val(*(__ptep)) & (_PAGE_READ | _PAGE_WRITE | _PAGE_EXEC))
@@ -315,42 +317,43 @@ void kvm_riscv_gstage_wp_range(struct kvm_gstage *gstage, gpa_t start, gpa_t end
}
}

+static bool __init kvm_riscv_hgatp_mode_supported(unsigned long mode)
+{
+ csr_write(CSR_HGATP, mode << HGATP_MODE_SHIFT);
+ return ((csr_read(CSR_HGATP) >> HGATP_MODE_SHIFT) == mode);
+}
+
void __init kvm_riscv_gstage_mode_detect(void)
{
+ kvm_riscv_gstage_supported_mode_mask = 0;
+ kvm_riscv_gstage_max_pgd_levels = 0;
+
#ifdef CONFIG_64BIT
- /* Try Sv57x4 G-stage mode */
- csr_write(CSR_HGATP, HGATP_MODE_SV57X4 << HGATP_MODE_SHIFT);
- if ((csr_read(CSR_HGATP) >> HGATP_MODE_SHIFT) == HGATP_MODE_SV57X4) {
- kvm_riscv_gstage_max_pgd_levels = 5;
- goto done;
+ /* Try Sv39x4 G-stage mode */
+ if (kvm_riscv_hgatp_mode_supported(HGATP_MODE_SV39X4)) {
+ kvm_riscv_gstage_supported_mode_mask |= BIT(HGATP_MODE_SV39X4);
+ kvm_riscv_gstage_max_pgd_levels = 3;
}

/* Try Sv48x4 G-stage mode */
- csr_write(CSR_HGATP, HGATP_MODE_SV48X4 << HGATP_MODE_SHIFT);
- if ((csr_read(CSR_HGATP) >> HGATP_MODE_SHIFT) == HGATP_MODE_SV48X4) {
+ if (kvm_riscv_hgatp_mode_supported(HGATP_MODE_SV48X4)) {
+ kvm_riscv_gstage_supported_mode_mask |= BIT(HGATP_MODE_SV48X4);
kvm_riscv_gstage_max_pgd_levels = 4;
- goto done;
}

- /* 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_max_pgd_levels = 3;
- goto done;
+ /* Try Sv57x4 G-stage mode */
+ if (kvm_riscv_hgatp_mode_supported(HGATP_MODE_SV57X4)) {
+ kvm_riscv_gstage_supported_mode_mask |= BIT(HGATP_MODE_SV57X4);
+ kvm_riscv_gstage_max_pgd_levels = 5;
}
#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) {
+ if (kvm_riscv_hgatp_mode_supported(HGATP_MODE_SV32X4)) {
+ kvm_riscv_gstage_supported_mode_mask |= BIT(HGATP_MODE_SV32X4);
kvm_riscv_gstage_max_pgd_levels = 2;
- goto done;
}
#endif

- /* KVM depends on !HGATP_MODE_OFF */
- kvm_riscv_gstage_max_pgd_levels = 0;
-
-done:
csr_write(CSR_HGATP, 0);
kvm_riscv_local_hfence_gvma_all();
}
--
2.50.1