Merge tag 'hyperv-next-signed-20251006' of git://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux

Pull hyperv updates from Wei Liu:

 - Unify guest entry code for KVM and MSHV (Sean Christopherson)

 - Switch Hyper-V MSI domain to use msi_create_parent_irq_domain()
   (Nam Cao)

 - Add CONFIG_HYPERV_VMBUS and limit the semantics of CONFIG_HYPERV
   (Mukesh Rathor)

 - Add kexec/kdump support on Azure CVMs (Vitaly Kuznetsov)

 - Deprecate hyperv_fb in favor of Hyper-V DRM driver (Prasanna
   Kumar T S M)

 - Miscellaneous enhancements, fixes and cleanups (Abhishek Tiwari,
   Alok Tiwari, Nuno Das Neves, Wei Liu, Roman Kisel, Michael Kelley)

* tag 'hyperv-next-signed-20251006' of git://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux:
  hyperv: Remove the spurious null directive line
  MAINTAINERS: Mark hyperv_fb driver Obsolete
  fbdev/hyperv_fb: deprecate this in favor of Hyper-V DRM driver
  Drivers: hv: Make CONFIG_HYPERV bool
  Drivers: hv: Add CONFIG_HYPERV_VMBUS option
  Drivers: hv: vmbus: Fix typos in vmbus_drv.c
  Drivers: hv: vmbus: Fix sysfs output format for ring buffer index
  Drivers: hv: vmbus: Clean up sscanf format specifier in target_cpu_store()
  x86/hyperv: Switch to msi_create_parent_irq_domain()
  mshv: Use common "entry virt" APIs to do work in root before running guest
  entry: Rename "kvm" entry code assets to "virt" to genericize APIs
  entry/kvm: KVM: Move KVM details related to signal/-EINTR into KVM proper
  mshv: Handle NEED_RESCHED_LAZY before transferring to guest
  x86/hyperv: Add kexec/kdump support on Azure CVMs
  Drivers: hv: Simplify data structures for VMBus channel close message
  Drivers: hv: util: Cosmetic changes for hv_utils_transport.c
  mshv: Add support for a new parent partition configuration
  clocksource: hyper-v: Skip unnecessary checks for the root partition
  hyperv: Add missing field to hv_output_map_device_interrupt

1 files changed, 10 insertions, 1 deletions

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index c78f860419d6..25773af116bc 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -565,6 +565,11 @@ static void __init ms_hyperv_init_platform(void)
 	machine_ops.crash_shutdown = hv_machine_crash_shutdown;
 #endif
 #endif
+	/*
+	 * HV_ACCESS_TSC_INVARIANT is always zero for the root partition. Root
+	 * partition doesn't need to write to synthetic MSR to enable invariant
+	 * TSC feature. It sees what the hardware provides.
+	 */
 	if (ms_hyperv.features & HV_ACCESS_TSC_INVARIANT) {
 		/*
 		 * Writing to synthetic MSR 0x40000118 updates/changes the
@@ -636,8 +641,12 @@ static void __init ms_hyperv_init_platform(void)
 	 * TSC should be marked as unstable only after Hyper-V
 	 * clocksource has been initialized. This ensures that the
 	 * stability of the sched_clock is not altered.
+	 *
+	 * HV_ACCESS_TSC_INVARIANT is always zero for the root partition. No
+	 * need to check for it.
 	 */
-	if (!(ms_hyperv.features & HV_ACCESS_TSC_INVARIANT))
+	if (!hv_root_partition() &&
+	    !(ms_hyperv.features & HV_ACCESS_TSC_INVARIANT))
 		mark_tsc_unstable("running on Hyper-V");
 
 	hardlockup_detector_disable();