• Konrad Rzeszutek Wilk's avatar
    xen/enlighten: Expose MWAIT and MWAIT_LEAF if hypervisor OKs it. · 73c154c6
    Konrad Rzeszutek Wilk authored
    For the hypervisor to take advantage of the MWAIT support it needs
    to extract from the ACPI _CST the register address. But the
    hypervisor does not have the support to parse DSDT so it relies on
    the initial domain (dom0) to parse the ACPI Power Management information
    and push it up to the hypervisor. The pushing of the data is done
    by the processor_harveset_xen module which parses the information that
    the ACPI parser has graciously exposed in 'struct acpi_processor'.
    
    For the ACPI parser to also expose the Cx states for MWAIT, we need
    to expose the MWAIT capability (leaf 1). Furthermore we also need to
    expose the MWAIT_LEAF capability (leaf 5) for cstate.c to properly
    function.
    
    The hypervisor could expose these flags when it traps the XEN_EMULATE_PREFIX
    operations, but it can't do it since it needs to be backwards compatible.
    Instead we choose to use the native CPUID to figure out if the MWAIT
    capability exists and use the XEN_SET_PDC query hypercall to figure out
    if the hypervisor wants us to expose the MWAIT_LEAF capability or not.
    
    Note: The XEN_SET_PDC query was implemented in c/s 23783:
    "ACPI: add _PDC input override mechanism".
    
    With this in place, instead of
     C3 ACPI IOPORT 415
    we get now
     C3:ACPI FFH INTEL MWAIT 0x20
    
    Note: The cpu_idle which would be calling the mwait variants for idling
    never gets set b/c we set the default pm_idle to be the hypercall variant.
    Acked-by: default avatarJan Beulich <JBeulich@suse.com>
    [v2: Fix missing header file include and #ifdef]
    Signed-off-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
    73c154c6
platform.h 10.5 KB