Merge tag 'hyperv-next-signed-20261028' of git://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linuxHEADmaster

Pull hyperv updates from Wei Liu:

 - Update to documents and code comments (Michael Kelley)

 - Harden Vmbus (Kameron Carr)

 - Rework MSHV driver page deposit logic (Mukesh Rathor)

 - Vmbus kexec bug fix (Shradha Gupta)

 - Miscellaneous bug fixes (Daehyeon Ko, Jiale Yao, Sasha Levin)

* tag 'hyperv-next-signed-20261028' of git://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux:
  Drivers: hv: Remove leftover support for old Hyper-V versions
  mshv: Remove unused *_old memory deposit functions
  mshv: Redesign hypervisor memory deposit logic
  mshv: Rename memory deposit memory functions to _old
  mshv_vtl: reject poll files with multiple waitqueues
  mshv_vtl: detach poll waiter on POLLFREE
  mshv_vtl: initialize poll file mutex before device registration
  Documentation: hyperv: Update information on guest CPU offlining
  Documentation: hyperv: Remove support for guests on Hyper-V 2012/2012R2
  Drivers: hv: Run VMBus kexec cleanup from syscore shutdown
  kexec: Add helper to report an active kexec reboot
  tools: hv: remove unused rte_smp_mb()
  Documentation: hyperv: Update documentation for sending VMBus packets
  Drivers: hv: vmbus: Check ACPI companion before use
  Documentation: hyperv: Describe validation of the ring buffer indices
  Drivers: hv: vmbus: Keep the ring byte counts sane for a bad index
  Drivers: hv: vmbus: Compute ring byte counts from a caller-held snapshot
  Drivers: hv: vmbus: Use *_ONCE() to access shared ring buffer indices
  Drivers: hv: vmbus: Bounds check the shared ring buffer indices

5 files changed, 37 insertions, 35 deletions

diff --git a/Documentation/networking/device_drivers/ethernet/microsoft/netvsc.rst b/Documentation/networking/device_drivers/ethernet/microsoft/netvsc.rst
index 616f808e885b..0d464706a59a 100644
--- a/Documentation/networking/device_drivers/ethernet/microsoft/netvsc.rst
+++ b/Documentation/networking/device_drivers/ethernet/microsoft/netvsc.rst
@@ -7,8 +7,9 @@ Hyper-V network driver
 Compatibility
 =============
 
-This driver is compatible with Windows Server 2012 R2, 2016 and
-Windows 10.
+This driver supports Linux guests running on Windows Server 2016 Hyper-V
+and later, and Windows 10 and later. Support for running as a guest on
+earlier versions of Hyper-V has been removed from Linux.
 
 Features
 ========
@@ -16,9 +17,8 @@ Features
 Checksum offload
 ----------------
   The netvsc driver supports checksum offload as long as the
-  Hyper-V host version does. Windows Server 2016 and Azure
-  support checksum offload for TCP and UDP for both IPv4 and
-  IPv6. Windows Server 2012 only supports checksum offload for TCP.
+  Hyper-V host version does. Windows Server 2016 Hyper-V and later, and
+  Azure, support checksum offload for TCP and UDP for both IPv4 and IPv6.
 
 Receive Side Scaling
 --------------------
@@ -58,8 +58,8 @@ Large Receive Offload (LRO), or Receive Side Coalescing (RSC)
 -------------------------------------------------------------
   The driver supports LRO/RSC in the vSwitch feature. It reduces the per packet
   processing overhead by coalescing multiple TCP segments when possible. The
-  feature is enabled by default on VMs running on Windows Server 2019 and
-  later. It may be changed by ethtool command::
+  feature is enabled by default on VMs running on Windows Server 2019 Hyper-V
+  and later. It may be changed by ethtool command::
 
 	ethtool -K eth0 lro on
 	ethtool -K eth0 lro off
diff --git a/Documentation/virt/hyperv/clocks.rst b/Documentation/virt/hyperv/clocks.rst
index 176043265803..9527e6073654 100644
--- a/Documentation/virt/hyperv/clocks.rst
+++ b/Documentation/virt/hyperv/clocks.rst
@@ -64,12 +64,8 @@ applying the scale and offset to get the constant 10 MHz clock.
 
 Linux clockevents are based on Hyper-V synthetic timer 0 (stimer0).
 While Hyper-V offers 4 synthetic timers for each CPU, Linux only uses
-timer 0. In older versions of Hyper-V, an interrupt from stimer0
-results in a VMBus control message that is demultiplexed by
-vmbus_isr() as described in the Documentation/virt/hyperv/vmbus.rst
-documentation. In newer versions of Hyper-V, stimer0 interrupts can
-be mapped to an architectural interrupt, which is referred to as
-"Direct Mode". Linux prefers to use Direct Mode when available. Since
+timer 0. stimer0 is operated in what Hyper-V calls "Direct Mode"
+where timer interrupts are mapped to an architectural interrupt. Since
 x86/x64 doesn't support per-CPU interrupts, Direct Mode statically
 allocates an x86 interrupt vector (HYPERV_STIMER0_VECTOR) across all CPUs
 and explicitly codes it to call the stimer0 interrupt handler. Hence
diff --git a/Documentation/virt/hyperv/coco.rst b/Documentation/virt/hyperv/coco.rst
index 3231e51444da..3e20249bd9b3 100644
--- a/Documentation/virt/hyperv/coco.rst
+++ b/Documentation/virt/hyperv/coco.rst
@@ -200,7 +200,10 @@ validation is performed. For messages passed from the host to the guest in a
 VMBus ring buffer, the length of the message is validated, and the message is
 copied into a temporary (encrypted) buffer for further validation and
 processing. The copying adds a small amount of overhead, but is the only way
-to protect against a malicious host. See hv_pkt_iter_first().
+to protect against a malicious host. See hv_pkt_iter_first(). Similarly, the
+ring buffer header is shared with the host, so the guest must snapshot and
+validate the read and write indices before using them to index into the ring
+buffer or to compute available space.
 
 Many drivers for VMBus devices have been "hardened" by adding code to fully
 validate messages received over VMBus, instead of assuming that Hyper-V is
diff --git a/Documentation/virt/hyperv/overview.rst b/Documentation/virt/hyperv/overview.rst
index 77408a89d1a4..6c1b9d4b6ddd 100644
--- a/Documentation/virt/hyperv/overview.rst
+++ b/Documentation/virt/hyperv/overview.rst
@@ -114,11 +114,13 @@ a shared page or remove an overlay page after the new kernel is
 using the page for a different purpose, corrupting the new kernel.
 Hyper-V does not provide a single "set everything" operation to
 guest VMs, so Linux code must individually revoke all sharing before
-doing kexec.   See hv_kexec_handler() and hv_crash_handler().  But
-the crash/panic path still has holes in cleanup because some shared
-pages are set using per-CPU synthetic registers and there's no
-mechanism to revoke the shared pages for CPUs other than the CPU
-running the panic path.
+doing kexec.  For a normal kexec reboot, the VMBus driver calls
+hv_kexec_handler() from its syscore shutdown callback, after device
+shutdown and before the architecture-specific machine shutdown.  The
+crash/panic path uses hv_crash_handler(), but still has holes in
+cleanup because some shared pages are set using per-CPU synthetic
+registers and there is no mechanism to revoke the shared pages for
+CPUs other than the CPU running the panic path.
 
 CPU Management
 --------------
@@ -132,11 +134,11 @@ Starting in Windows Server 2022 Hyper-V, the ACPI tables reflect
 only the CPUs actually present in the VM, so Linux does not report
 any hot-add CPUs.
 
-A Linux guest CPU may be taken offline using the normal Linux
-mechanisms, provided no VMBus channel interrupts are assigned to
-the CPU.  See the section on VMBus Interrupts for more details
-on how VMBus channel interrupts can be re-assigned to permit
-taking a CPU offline.
+A Linux guest CPU may be taken offline, and subsequently brought
+back online, using the normal Linux mechanisms. See the "VMBus
+Interrupts" section of Documentation/virt/hyperv/vmbus.rst
+documentation for how VMBus channel interrupts are automatically
+re-assigned if necessary when taking a CPU offline.
 
 32-bit and 64-bit
 -----------------
@@ -157,9 +159,9 @@ when accessing data shared with Hyper-V.
 Versioning
 ----------
 Current Linux kernels operate correctly with older versions of
-Hyper-V back to Windows Server 2012 Hyper-V. Support for running
-on the original Hyper-V release in Windows Server 2008/2008 R2
-has been removed.
+Hyper-V back to Windows Server 2016 Hyper-V and Windows 10. Support for
+running on Windows Server 2012/2012 R2, Windows Server 2008/2008 R2,
+and Windows 8.1 and earlier has been removed.
 
 A Linux guest on Hyper-V outputs in dmesg the version of Hyper-V
 it is running on.  This version is in the form of a Windows build
diff --git a/Documentation/virt/hyperv/vmbus.rst b/Documentation/virt/hyperv/vmbus.rst
index 654bb4849972..c546e821ce6b 100644
--- a/Documentation/virt/hyperv/vmbus.rst
+++ b/Documentation/virt/hyperv/vmbus.rst
@@ -141,14 +141,15 @@ Three functions exist to send VMBus channel messages:
 
 1. vmbus_sendpacket():  Control-only messages and messages with
    embedded data -- no GPAs
-2. vmbus_sendpacket_pagebuffer(): Message with list of GPAs
-   identifying data to transfer.  An offset and length is
-   associated with each GPA so that multiple discontinuous areas
-   of guest memory can be targeted.
-3. vmbus_sendpacket_mpb_desc(): Message with list of GPAs
-   identifying data to transfer.  A single offset and length is
-   associated with a list of GPAs.  The GPAs must describe a
-   single logical area of guest memory to be targeted.
+2. vmbus_sendpacket_getid(): Similar to vmbus_sendpacket() but returns
+   a transaction ID that is matched against a reply from the Hyper-V
+   host. Useful when the struct completion (or other rendezvous data)
+   must reside on the caller's stack. By invalidating the transaction
+   ID before exiting the function due to a timeout or other error, a
+   late arriving interrupt is assured to not trash the stack.
+3. vmbus_sendpacket_mpb_desc(): Message with one or more data ranges
+   to target. Each range consists of a single offset and length plus
+   a list of GPAs that describe a logical area of guest memory.
 
 Historically, Linux guests have trusted Hyper-V to send well-formed
 and valid messages, and Linux drivers for synthetic devices did not