From 93de2a6a4b91b72607136dd656edf03fb399d27f Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Wed, 23 Sep 2026 09:37:21 -0700 Subject: KVM: SEV: Do cache maintenance on the source VM during intra-host migration Manually perform cache maintenance on the source VM during intra-host migration to ensure no stale data is left in CPU caches after the VM is destroyed. Because the source VM is "converted" to a non-SEV VM, KVM's memory reclaim flows won't trigger cache maintenance, e.g. when all guest memory is reclaimed in response to detaching from the mmu_notifier. Note, relying on the destination VM to do cache maintenance isn't an option as KVM doesn't require identical guest memory configurations, i.e. the source VM may have access to memory that the destination VM does not. Enforcing equivalent memory configurations is infeasible, as it would require a *deep* comparison of memslots, e.g. to verify that not only are the memslot identical, but what the memslots point at is also identical. Fixes: b56639318bb2 ("KVM: SEV: Add support for SEV intra host migration") Cc: stable@vger.kernel.org Reported-by: Stefan Teodorescu Signed-off-by: Sean Christopherson Message-ID: <20260923163721.1584779-3-seanjc@google.com> Signed-off-by: Paolo Bonzini --- Documentation/driver-api/driver-model/overview.rst | 124 +++++++++++++++++++++ 1 file changed, 124 insertions(+) create mode 100644 Documentation/driver-api/driver-model/overview.rst (limited to 'Documentation/driver-api/driver-model/overview.rst') diff --git a/Documentation/driver-api/driver-model/overview.rst b/Documentation/driver-api/driver-model/overview.rst new file mode 100644 index 000000000..b3f447bf9 --- /dev/null +++ b/Documentation/driver-api/driver-model/overview.rst @@ -0,0 +1,124 @@ +============================= +The Linux Kernel Device Model +============================= + +Patrick Mochel + +Drafted 26 August 2002 +Updated 31 January 2006 + + +Overview +~~~~~~~~ + +The Linux Kernel Driver Model is a unification of all the disparate driver +models that were previously used in the kernel. It is intended to augment the +bus-specific drivers for bridges and devices by consolidating a set of data +and operations into globally accessible data structures. + +Traditional driver models implemented some sort of tree-like structure +(sometimes just a list) for the devices they control. There wasn't any +uniformity across the different bus types. + +The current driver model provides a common, uniform data model for describing +a bus and the devices that can appear under the bus. The unified bus +model includes a set of common attributes which all buses carry, and a set +of common callbacks, such as device discovery during bus probing, bus +shutdown, bus power management, etc. + +The common device and bridge interface reflects the goals of the modern +computer: namely the ability to do seamless device "plug and play", power +management, and hot plug. In particular, the model dictated by Intel and +Microsoft (namely ACPI) ensures that almost every device on almost any bus +on an x86-compatible system can work within this paradigm. Of course, +not every bus is able to support all such operations, although most +buses support most of those operations. + + +Downstream Access +~~~~~~~~~~~~~~~~~ + +Common data fields have been moved out of individual bus layers into a common +data structure. These fields must still be accessed by the bus layers, +and sometimes by the device-specific drivers. + +Other bus layers are encouraged to do what has been done for the PCI layer. +struct pci_dev now looks like this:: + + struct pci_dev { + ... + + struct device dev; /* Generic device interface */ + ... + }; + +Note first that the struct device dev within the struct pci_dev is +statically allocated. This means only one allocation on device discovery. + +Note also that that struct device dev is not necessarily defined at the +front of the pci_dev structure. This is to make people think about what +they're doing when switching between the bus driver and the global driver, +and to discourage meaningless and incorrect casts between the two. + +The PCI bus layer freely accesses the fields of struct device. It knows about +the structure of struct pci_dev, and it should know the structure of struct +device. Individual PCI device drivers that have been converted to the current +driver model generally do not and should not touch the fields of struct device, +unless there is a compelling reason to do so. + +The above abstraction prevents unnecessary pain during transitional phases. +If it were not done this way, then when a field was renamed or removed, every +downstream driver would break. On the other hand, if only the bus layer +(and not the device layer) accesses the struct device, it is only the bus +layer that needs to change. + + +User Interface +~~~~~~~~~~~~~~ + +By virtue of having a complete hierarchical view of all the devices in the +system, exporting a complete hierarchical view to userspace becomes relatively +easy. This has been accomplished by implementing a special purpose virtual +file system named sysfs. + +Almost all mainstream Linux distros mount this filesystem automatically; you +can see some variation of the following in the output of the "mount" command:: + + $ mount + ... + none on /sys type sysfs (rw,noexec,nosuid,nodev) + ... + $ + +The auto-mounting of sysfs is typically accomplished by an entry similar to +the following in the /etc/fstab file:: + + none /sys sysfs defaults 0 0 + +or something similar in the /lib/init/fstab file on Debian-based systems:: + + none /sys sysfs nodev,noexec,nosuid 0 0 + +If sysfs is not automatically mounted, you can always do it manually with:: + + # mount -t sysfs sysfs /sys + +Whenever a device is inserted into the tree, a directory is created for it. +This directory may be populated at each layer of discovery - the global layer, +the bus layer, or the device layer. + +The global layer currently creates two files - 'name' and 'power'. The +former only reports the name of the device. The latter reports the +current power state of the device. It will also be used to set the current +power state. + +The bus layer may also create files for the devices it finds while probing the +bus. For example, the PCI layer currently creates 'irq' and 'resource' files +for each PCI device. + +A device-specific driver may also export files in its directory to expose +device-specific data or tunable interfaces. + +More information about the sysfs directory layout can be found in +the other documents in this directory and in the file +Documentation/filesystems/sysfs.rst. -- cgit v1.3.1