vfio/pci: Invalidate mmaps and block the access in D3hot power state

According to [PCIe v5 5.3.1.4.1] for D3hot state

 "Configuration and Message requests are the only TLPs accepted by a
  Function in the D3Hot state. All other received Requests must be
  handled as Unsupported Requests, and all received Completions may
  optionally be handled as Unexpected Completions."

Currently, if the vfio PCI device has been put into D3hot state and if
user makes non-config related read/write request in D3hot state, these
requests will be forwarded to the host and this access may cause
issues on a few systems.

This patch leverages the memory-disable support added in commit
'abafbc551fdd ("vfio-pci: Invalidate mmaps and block MMIO access on
disabled memory")' to generate page fault on mmap access and
return error for the direct read/write. If the device is D3hot state,
then the error will be returned for MMIO access. The IO access generally
does not make the system unresponsive so the IO access can still happen
in D3hot state. The default value should be returned in this case
without bringing down the complete system.

Also, the power related structure fields need to be protected so
we can use the same 'memory_lock' to protect these fields also.
This protection is mainly needed when user changes the PCI
power state by writing into PCI_PM_CTRL register.
vfio_lock_and_set_power_state() wrapper function will take the
required locks and then it will invoke the vfio_pci_set_power_state().

Signed-off-by: Abhishek Sahu <abhsahu@nvidia.com>
Link: https://lore.kernel.org/r/20220518111612.16985-2-abhsahu@nvidia.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

Author: abhsahu

drivers/vfio/pci/vfio_pci_config.c

@@ -402,11 +402,14 @@ bool __vfio_pci_memory_enabled(struct vfio_pci_core_device *vdev)
 	u16 cmd = le16_to_cpu(*(__le16 *)&vdev->vconfig[PCI_COMMAND]);
 
 	/*
+	 * Memory region cannot be accessed if device power state is D3.
+	 *
 	 * SR-IOV VF memory enable is handled by the MSE bit in the
 	 * PF SR-IOV capability, there's therefore no need to trigger
 	 * faults based on the virtual value.
 	 */
-	return pdev->no_command_memory || (cmd & PCI_COMMAND_MEMORY);
+	return pdev->current_state < PCI_D3hot &&
+	       (pdev->no_command_memory || (cmd & PCI_COMMAND_MEMORY));
 }
 
 /*
@@ -692,6 +695,22 @@ static int __init init_pci_cap_basic_perm(struct perm_bits *perm)
 	return 0;
 }
 
+/*
+ * It takes all the required locks to protect the access of power related
+ * variables and then invokes vfio_pci_set_power_state().
+ */
+static void vfio_lock_and_set_power_state(struct vfio_pci_core_device *vdev,
+					  pci_power_t state)
+{
+	if (state >= PCI_D3hot)
+		vfio_pci_zap_and_down_write_memory_lock(vdev);
+	else
+		down_write(&vdev->memory_lock);
+
+	vfio_pci_set_power_state(vdev, state);
+	up_write(&vdev->memory_lock);
+}
+
 static int vfio_pm_config_write(struct vfio_pci_core_device *vdev, int pos,
 				int count, struct perm_bits *perm,
 				int offset, __le32 val)
@@ -718,7 +737,7 @@ static int vfio_pm_config_write(struct vfio_pci_core_device *vdev, int pos,
 			break;
 		}
 
-		vfio_pci_set_power_state(vdev, state);
+		vfio_lock_and_set_power_state(vdev, state);
 	}
 
 	return count;