• Alok Kataria's avatar
    x86: Hypervisor detection and get tsc_freq from hypervisor · 88b094fb
    Alok Kataria authored
    Impact: Changes timebase calibration on Vmware.
    
    v3->v2 : Abstract the hypervisor detection and feature (tsc_freq) request
    	 behind a hypervisor.c file
    v2->v1 : Add a x86_hyper_vendor field to the cpuinfo_x86 structure.
    	 This avoids multiple calls to the hypervisor detection function.
    
    This patch adds function to detect if we are running under VMware.
    The current way to check if we are on VMware is following,
    #  check if "hypervisor present bit" is set, if so read the 0x40000000
       cpuid leaf and check for "VMwareVMware" signature.
    #  if the above fails, check the DMI vendors name for "VMware" string
       if we find one we query the VMware hypervisor port to check if we are
       under VMware.
    
    The DMI + "VMware hypervisor port check" is needed for older VMware products,
    which don't implement the hypervisor signature cpuid leaf.
    Also note that since we are checking for the DMI signature the hypervisor
    port should never be accessed on native hardware.
    
    This patch also adds a hypervisor_get_tsc_freq function, instead of
    calibrating the frequency which can be error prone in virtualized
    environment, we ask the hypervisor for it. We get the frequency from
    the hypervisor by accessing the hypervisor port if we are running on VMware.
    Other hypervisors too can add code to the generic routine to get frequency on
    their platform.
    Signed-off-by: default avatarAlok N Kataria <akataria@vmware.com>
    Signed-off-by: default avatarDan Hecht <dhecht@vmware.com>
    Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
    88b094fb
tsc.c 21.6 KB