[PATCH 6/6] LoongArch: KVM: Reject repeated PCH-PIC CTRL_INIT

[Tao Cui <cui.tao@linux.dev>]

From: Tao Cui <cuitao@kylinos.cn>

KVM_DEV_LOONGARCH_PCH_PIC_CTRL_INIT has no guard against repeated
invocation: every call overwrites pch_pic_base and registers the same
kvm_io_device on the MMIO bus at the new address, while
kvm_pch_pic_destroy() unregisters only one bus range.  After a repeated
init, MMIO to the stale ranges computes its register offset against the
new base and silently reads 0 / drops writes, and the leftover bus
entries persist until the VM is destroyed.

Reject a repeated init with -EBUSY, a null address with -EINVAL, and
only set pch_pic_base after the bus registration succeeds so a failed
init does not leave the device half-initialized.  The registration
error is propagated instead of being replaced with -EFAULT.

Fixes: d206d9514873 ("LoongArch: KVM: Add PCHPIC user mode read and write functions")
Signed-off-by: Tao Cui <cuitao@kylinos.cn>
---
 arch/loongarch/kvm/intc/pch_pic.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/loongarch/kvm/intc/pch_pic.c b/arch/loongarch/kvm/intc/pch_pic.c
index 136211f154d4..2baf9ecf0c8a 100644
--- a/arch/loongarch/kvm/intc/pch_pic.c
+++ b/arch/loongarch/kvm/intc/pch_pic.c
@@ -285,7 +285,10 @@ static int kvm_pch_pic_init(struct kvm_device *dev, u64 addr)
 	struct kvm_io_device *device;
 	struct loongarch_pch_pic *s = dev->kvm->arch.pch_pic;
 
-	s->pch_pic_base = addr;
+	if (!addr)
+		return -EINVAL;
+	if (s->pch_pic_base)
+		return -EBUSY;
 	device = &s->device;
 	/* init device by pch pic writing and reading ops */
 	kvm_iodevice_init(device, &kvm_pch_pic_ops);
@@ -293,8 +296,11 @@ static int kvm_pch_pic_init(struct kvm_device *dev, u64 addr)
 	/* register pch pic device */
 	ret = kvm_io_bus_register_dev(kvm, KVM_MMIO_BUS, addr, PCH_PIC_SIZE, device);
 	mutex_unlock(&kvm->slots_lock);
+	if (ret < 0)
+		return ret;
 
-	return (ret < 0) ? -EFAULT : 0;
+	s->pch_pic_base = addr;
+	return 0;
 }
 
 /* used by user space to get or set pch pic registers */
-- 
2.43.0