KVM: x86: Fix KVM clock precision in get_kvmclock() with TSC scaling

When in master clock mode, the KVM clock is defined in terms of the
guest TSC. But get_kvmclock() was computing it from the host TSC
without applying TSC scaling, leading to a systemic drift from the
values the guest computes from its own TSC.

Store the VM's TSC scaling ratio in kvm_arch and precompute the
guest-TSC-based mul/shift in pvclock_update_vm_gtod_copy(). Use these
in get_kvmclock() to scale the host TSC delta to guest TSC before
converting to nanoseconds.

This avoids "definition C" of the KVM clock described in commit
633d7652f80f ("KVM: x86/xen: Do not corrupt KVM clock in
kvm_xen_shared_info_init()").

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Link: https://patch.msgid.link/20260826213303.914988-12-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

0 files changed, 0 insertions, 0 deletions