[PATCH v5 3/3] 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 repeated initialization with -EEXIST, using the initialized
state of the kvm_io_device as the indicator.  The check, the MMIO base
update and the bus registration are serialized by slots_lock, and the
real registration error is propagated instead of being replaced with
-EFAULT.  On a registration failure the base and the device state are
rolled back so that a retry can start over.

Fixes: d206d9514873 ("LoongArch: KVM: Add PCHPIC user mode read and write functions")
Signed-off-by: Tao Cui <cuitao@kylinos.cn>
Reviewed-by: Bibo Mao <maobibo@loongson.cn>
---
 arch/loongarch/kvm/intc/pch_pic.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/arch/loongarch/kvm/intc/pch_pic.c b/arch/loongarch/kvm/intc/pch_pic.c
index 51e4a6a39dc0..ee06bdfd6547 100644
--- a/arch/loongarch/kvm/intc/pch_pic.c
+++ b/arch/loongarch/kvm/intc/pch_pic.c
@@ -281,16 +281,26 @@ 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;
 	device = &s->device;
+	mutex_lock(&kvm->slots_lock);
+	if (s->device.ops) {
+		ret = -EEXIST;
+		goto out;
+	}
+	s->pch_pic_base = addr;
 	/* init device by pch pic writing and reading ops */
 	kvm_iodevice_init(device, &kvm_pch_pic_ops);
-	mutex_lock(&kvm->slots_lock);
 	/* register pch pic device */
 	ret = kvm_io_bus_register_dev(kvm, KVM_MMIO_BUS, addr, PCH_PIC_SIZE, device);
+	if (ret) {
+		/* undo the state so that a retry can start over */
+		s->pch_pic_base = 0;
+		s->device.ops = NULL;
+	}
+out:
 	mutex_unlock(&kvm->slots_lock);
 
-	return (ret < 0) ? -EFAULT : 0;
+	return ret;
 }
 
 /* used by user space to get or set pch pic registers */
-- 
2.43.0