Documentation: hyperv: Remove support for guests on Hyper-V 2012/2012R2

Support for running Linux guests on Windows Server 2012/2012 R2 Hyper-V
hosts and Windows 8/8.1 hosts has been removed, which includes removing
support for operating Hyper-V synthetic timers in other than Direct Mode.
Update the documentation to reflect these removals.

Signed-off-by: Michael Kelley <mhklinux@outlook.com>
Reviewed-by: Naman Jain <namjain@linux.microsoft.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>

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

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

Documentation/virt/hyperv/overview.rst

@@ -159,9 +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