• Suresh Siddha's avatar
    x86, pat/mtrr: Rendezvous all the cpus for MTRR/PAT init · d0af9eed
    Suresh Siddha authored
    SDM Vol 3a section titled "MTRR considerations in MP systems" specifies
    the need for synchronizing the logical cpu's while initializing/updating
    MTRR.
    
    Currently Linux kernel does the synchronization of all cpu's only when
    a single MTRR register is programmed/updated. During an AP online
    (during boot/cpu-online/resume)  where we initialize all the MTRR/PAT registers,
    we don't follow this synchronization algorithm.
    
    This can lead to scenarios where during a dynamic cpu online, that logical cpu
    is initializing MTRR/PAT with cache disabled (cr0.cd=1) etc while other logical
    HT sibling continue to run (also with cache disabled because of cr0.cd=1
    on its sibling).
    
    Starting from Westmere, VMX transitions with cr0.cd=1 don't work properly
    (because of some VMX performance optimizations) and the above scenario
    (with one logical cpu doing VMX activity and another logical cpu coming online)
    can result in system crash.
    
    Fix the MTRR initialization by doing rendezvous of all the cpus. During
    boot and resume, we delay the MTRR/PAT init for APs till all the
    logical cpu's come online and the rendezvous process at the end of AP's bringup,
    will initialize the MTRR/PAT for all AP's.
    
    For dynamic single cpu online, we synchronize all the logical cpus and
    do the MTRR/PAT init on the AP that is coming online.
    Signed-off-by: default avatarSuresh Siddha <suresh.b.siddha@intel.com>
    Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
    d0af9eed
cpu.c 13.9 KB