• Igor Druzhinin's avatar
    xen/pci: reserve MCFG areas earlier · a4098bc6
    Igor Druzhinin authored
    If MCFG area is not reserved in E820, Xen by default will defer its usage
    until Dom0 registers it explicitly after ACPI parser recognizes it as
    a reserved resource in DSDT. Having it reserved in E820 is not
    mandatory according to "PCI Firmware Specification, rev 3.2" (par. 4.1.2)
    and firmware is free to keep a hole in E820 in that place. Xen doesn't know
    what exactly is inside this hole since it lacks full ACPI view of the
    platform therefore it's potentially harmful to access MCFG region
    without additional checks as some machines are known to provide
    inconsistent information on the size of the region.
    
    Now xen_mcfg_late() runs after acpi_init() which is too late as some basic
    PCI enumeration starts exactly there as well. Trying to register a device
    prior to MCFG reservation causes multiple problems with PCIe extended
    capability initializations in Xen (e.g. SR-IOV VF BAR sizing). There are
    no convenient hooks for us to subscribe to so register MCFG areas earlier
    upon the first invocation of xen_add_device(). It should be safe to do once
    since all the boot time buses must have their MCFG areas in MCFG table
    already and we don't support PCI bus hot-plug.
    Signed-off-by: default avatarIgor Druzhinin <igor.druzhinin@citrix.com>
    Reviewed-by: default avatarBoris Ostrovsky <boris.ostrovsky@oracle.com>
    Signed-off-by: default avatarBoris Ostrovsky <boris.ostrovsky@oracle.com>
    a4098bc6
pci.c 5.64 KB