diff options
| author | Michael Kelley <mhklinux@outlook.com> | 2025-05-19 21:44:35 -0700 |
|---|---|---|
| committer | Wei Liu <wei.liu@kernel.org> | 2025-05-23 16:30:56 +0000 |
| commit | f77276d1c9597ade06f3facbceb51bd1abf1bd5c (patch) | |
| tree | 64bbeffe0e405da451a638589d58a024e0441f2f | |
| parent | dd1af0c4c56d7c60eaf7f30f9d816ed1befbd7d7 (diff) | |
Documentation: hyperv: Update VMBus doc with new features and info
Starting in the 6.15 kernel, VMBus interrupts are automatically
assigned away from a CPU that is being taken offline. Add documentation
describing this case.
Also add details of Hyper-V behavior when the primary channel of
a VMBus device is closed as the result of unbinding the device's
driver. This behavior has not changed, but it was not previously
documented.
Signed-off-by: Michael Kelley <mhklinux@outlook.com>
Link: https://lore.kernel.org/r/20250520044435.7734-1-mhklinux@outlook.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Message-ID: <20250520044435.7734-1-mhklinux@outlook.com>
| -rw-r--r-- | Documentation/virt/hyperv/vmbus.rst | 28 |
1 files changed, 24 insertions, 4 deletions
diff --git a/Documentation/virt/hyperv/vmbus.rst b/Documentation/virt/hyperv/vmbus.rst index 1dcef6a7fda3..654bb4849972 100644 --- a/Documentation/virt/hyperv/vmbus.rst +++ b/Documentation/virt/hyperv/vmbus.rst @@ -250,10 +250,18 @@ interrupts are not Linux IRQs, there are no entries in /proc/interrupts or /proc/irq corresponding to individual VMBus channel interrupts. An online CPU in a Linux guest may not be taken offline if it has -VMBus channel interrupts assigned to it. Any such channel -interrupts must first be manually reassigned to another CPU as -described above. When no channel interrupts are assigned to the -CPU, it can be taken offline. +VMBus channel interrupts assigned to it. Starting in kernel v6.15, +any such interrupts are automatically reassigned to some other CPU +at the time of offlining. The "other" CPU is chosen by the +implementation and is not load balanced or otherwise intelligently +determined. If the CPU is onlined again, channel interrupts previously +assigned to it are not moved back. As a result, after multiple CPUs +have been offlined, and perhaps onlined again, the interrupt-to-CPU +mapping may be scrambled and non-optimal. In such a case, optimal +assignments must be re-established manually. For kernels v6.14 and +earlier, any conflicting channel interrupts must first be manually +reassigned to another CPU as described above. Then when no channel +interrupts are assigned to the CPU, it can be taken offline. The VMBus channel interrupt handling code is designed to work correctly even if an interrupt is received on a CPU other than the @@ -324,3 +332,15 @@ rescinded, neither Hyper-V nor Linux retains any state about its previous existence. Such a device might be re-added later, in which case it is treated as an entirely new device. See vmbus_onoffer_rescind(). + +For some devices, such as the KVP device, Hyper-V automatically +sends a rescind message when the primary channel is closed, +likely as a result of unbinding the device from its driver. +The rescind causes Linux to remove the device. But then Hyper-V +immediately reoffers the device to the guest, causing a new +instance of the device to be created in Linux. For other +devices, such as the synthetic SCSI and NIC devices, closing the +primary channel does *not* result in Hyper-V sending a rescind +message. The device continues to exist in Linux on the VMBus, +but with no driver bound to it. The same driver or a new driver +can subsequently be bound to the existing instance of the device. |