• Michael Neuling's avatar
    KVM: PPC: Book3S HV: Check for updated HDSISR on P9 HDSI exception · e001fa78
    Michael Neuling authored
    On POWER9 DD2.1 and below, sometimes on a Hypervisor Data Storage
    Interrupt (HDSI) the HDSISR is not be updated at all.
    
    To work around this we put a canary value into the HDSISR before
    returning to a guest and then check for this canary when we take a
    HDSI. If we find the canary on a HDSI, we know the hardware didn't
    update the HDSISR. In this case we return to the guest to retake the
    HDSI which should correctly update the HDSISR the second time HDSI
    entry.
    
    After talking to Paulus we've applied this workaround to all POWER9
    CPUs. The workaround of returning to the guest shouldn't ever be
    triggered on well behaving CPU. The extra instructions should have
    negligible performance impact.
    Signed-off-by: default avatarMichael Neuling <mikey@neuling.org>
    Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
    e001fa78
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