cxl: Drop commands if the PCI channel is not in normal state

If the PCI channel has gone down, don't attempt to poke the hardware.

We need to guard every time cxl_whatever_(read|write) is called. This
is because a call to those functions will dereference an offset into an
mmio register, and the mmio mappings get invalidated in the EEH
teardown.

Check in the read/write functions in the header.
We give them the same semantics as usual PCI operations:
 - a write to a channel that is down is ignored.
 - a read from a channel that is down returns all fs.

Also, we try to access the MMIO space of a vPHB device as part of the
PCI disable path. Because that's a read that bypasses most of our usual
checks, we handle it explicitly.

As far as user visible warnings go:
 - Check link state in file ops, return -EIO if down.
 - Be reasonably quiet if there's an error in a teardown path,
   or when we already know the hardware is going down.
 - Throw a big WARN if someone tries to start a CXL operation
   while the card is down. This gives a useful stacktrace for
   debugging whatever is doing that.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 19 insertions, 0 deletions

diff --git a/drivers/misc/cxl/file.c b/drivers/misc/cxl/file.c
index c8c8bfa2679b..57bdb473749f 100644
--- a/drivers/misc/cxl/file.c
+++ b/drivers/misc/cxl/file.c
@@ -73,6 +73,11 @@ static int __afu_open(struct inode *inode, struct file *file, bool master)
 	if (!afu->current_mode)
 		goto err_put_afu;
 
+	if (!cxl_adapter_link_ok(adapter)) {
+		rc = -EIO;
+		goto err_put_afu;
+	}
+
 	if (!(ctx = cxl_context_alloc())) {
 		rc = -ENOMEM;
 		goto err_put_afu;
@@ -238,6 +243,9 @@ long afu_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 	if (ctx->status == CLOSED)
 		return -EIO;
 
+	if (!cxl_adapter_link_ok(ctx->afu->adapter))
+		return -EIO;
+
 	pr_devel("afu_ioctl\n");
 	switch (cmd) {
 	case CXL_IOCTL_START_WORK:
@@ -265,6 +273,9 @@ int afu_mmap(struct file *file, struct vm_area_struct *vm)
 	if (ctx->status != STARTED)
 		return -EIO;
 
+	if (!cxl_adapter_link_ok(ctx->afu->adapter))
+		return -EIO;
+
 	return cxl_context_iomap(ctx, vm);
 }
 
@@ -309,6 +320,9 @@ ssize_t afu_read(struct file *file, char __user *buf, size_t count,
 	int rc;
 	DEFINE_WAIT(wait);
 
+	if (!cxl_adapter_link_ok(ctx->afu->adapter))
+		return -EIO;
+
 	if (count < CXL_READ_MIN_SIZE)
 		return -EINVAL;
 
@@ -319,6 +333,11 @@ ssize_t afu_read(struct file *file, char __user *buf, size_t count,
 		if (ctx_event_pending(ctx))
 			break;
 
+		if (!cxl_adapter_link_ok(ctx->afu->adapter)) {
+			rc = -EIO;
+			goto out;
+		}
+
 		if (file->f_flags & O_NONBLOCK) {
 			rc = -EAGAIN;
 			goto out;