[PATCH v2 2/2] RISC-V: KVM: Disallow GPA-width changes after AIA init

[Pengpeng Hou <hppiscas@163.com>]

KVM_ENABLE_CAP(KVM_CAP_VM_GPA_BITS) allows userspace to reduce the
stage-2 GPA width while a VM has no vCPUs or memory slots.

AIA initialization can complete with an APLIC and no vCPUs or memory
slots. The APLIC MMIO device has then been registered, but the existing
checks still allow userspace to shrink the GPA width below its address.

Reject GPA-width changes after AIA initialization. Both paths hold
kvm->lock, serializing the width change with AIA initialization.

The issue was found by our static-analysis tool.

Fixes: 7263b4fdb0b2 ("RISC-V: KVM: Reuse KVM_CAP_VM_GPA_BITS to select HGATP.MODE")
Reviewed-by: Anup Patel <anup@brainfault.org>
Assisted-by: gpt 5
Signed-off-by: Pengpeng Hou <hppiscas@163.com>
---
Changes since v1: https://lore.kernel.org/r/4852f3b8985c353811fa065e4701d76dc9a7f086.1786512671.git.pengpeng@iscas.ac.cn/
- No change to the code; retain Anup's Reviewed-by.
- Rebase and clarify the locking description.

 arch/riscv/kvm/vm.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/kvm/vm.c b/arch/riscv/kvm/vm.c
index a9f083f..66edfaa 100644
--- a/arch/riscv/kvm/vm.c
+++ b/arch/riscv/kvm/vm.c
@@ -250,7 +250,8 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap)
 		mutex_lock(&kvm->lock);
 		mutex_lock(&kvm->slots_lock);
 
-		if (kvm->created_vcpus || !kvm_are_all_memslots_empty(kvm))
+		if (kvm->created_vcpus || !kvm_are_all_memslots_empty(kvm) ||
+		    kvm_riscv_aia_initialized(kvm))
 			r = -EBUSY;
 		else
 			kvm->arch.pgd_levels = new_levels;