[PATCH 3/3] RISC-V: KVM: Introduce extension_enabled

[Andrew Jones]

We need three SBI extension status values (uninitialized, enabled,
and disabled). Pairing another boolean array, extension_enabled[],
with the boolean array extension_disabled[] provides four states.
Using a pair of boolean arrays, which may eventually be changed to
a pair of bitmaps, is more space efficient than using one enum
status field. Apply the new (enabled=1,disabled=0) state, which
means either the extension doesn't have a probe function or that
its probe was successful, to avoid more than one probe of the
extension.

Signed-off-by: Andrew Jones <ajones at ventanamicro.com>
---
 arch/riscv/include/asm/kvm_vcpu_sbi.h |  9 +++++++++
 arch/riscv/kvm/vcpu_sbi.c             | 11 ++++++++++-
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/include/asm/kvm_vcpu_sbi.h b/arch/riscv/include/asm/kvm_vcpu_sbi.h
index 4278125a38a5..e3c5e1d15e93 100644
--- a/arch/riscv/include/asm/kvm_vcpu_sbi.h
+++ b/arch/riscv/include/asm/kvm_vcpu_sbi.h
@@ -16,6 +16,15 @@
 
 struct kvm_vcpu_sbi_context {
 	int return_handled;
+	/*
+	 * extension_enabled[] and extension_disabled[] provide SBI
+	 * extensions four status values, of which we need three:
+	 * (0,0) uninitialized, (1,0) enabled, (0,1) disabled. Using
+	 * a pair of boolean arrays, which may eventually be changed
+	 * to a pair of bitmaps, is more space efficient than using
+	 * one enum status field.
+	 */
+	bool extension_enabled[KVM_RISCV_SBI_EXT_MAX];
 	bool extension_disabled[KVM_RISCV_SBI_EXT_MAX];
 };
 
diff --git a/arch/riscv/kvm/vcpu_sbi.c b/arch/riscv/kvm/vcpu_sbi.c
index a1a82f0fbad2..344d38bbe06a 100644
--- a/arch/riscv/kvm/vcpu_sbi.c
+++ b/arch/riscv/kvm/vcpu_sbi.c
@@ -155,6 +155,12 @@ static int riscv_vcpu_set_sbi_ext_single(struct kvm_vcpu *vcpu,
 	if (!sext)
 		return -ENOENT;
 
+	/*
+	 * We can't set scontext->extension_enabled[] to reg_val since the
+	 * extension may have a probe() function which needs to confirm
+	 * enablement first. Only set extension_disabled[] here and leave
+	 * the extension_enabled[] setting to kvm_vcpu_sbi_find_ext().
+	 */
 	scontext->extension_disabled[sext->ext_idx] = !reg_val;
 
 	return 0;
@@ -317,7 +323,8 @@ const struct kvm_vcpu_sbi_extension *kvm_vcpu_sbi_find_ext(
 		ext = entry->ext_ptr;
 
 		if (ext->extid_start <= extid && ext->extid_end >= extid) {
-			if (entry->ext_idx >= KVM_RISCV_SBI_EXT_MAX)
+			if (entry->ext_idx >= KVM_RISCV_SBI_EXT_MAX ||
+			    scontext->extension_enabled[entry->ext_idx])
 				return ext;
 			if (scontext->extension_disabled[entry->ext_idx])
 				return NULL;
@@ -325,6 +332,8 @@ const struct kvm_vcpu_sbi_extension *kvm_vcpu_sbi_find_ext(
 				scontext->extension_disabled[entry->ext_idx] = true;
 				return NULL;
 			}
+
+			scontext->extension_enabled[entry->ext_idx] = true;
 			return ext;
 		}
 	}
-- 
2.39.2