• James Morse's avatar
    KVM: arm64: Defer guest entry when an asynchronous exception is pending · 5dcd0fdb
    James Morse authored
    SError that occur during world-switch's entry to the guest will be
    accounted to the guest, as the exception is masked until we enter the
    guest... but we want to attribute the SError as precisely as possible.
    
    Reading DISR_EL1 before guest entry requires free registers, and using
    ESB+DISR_EL1 to consume and read back the ESR would leave KVM holding
    a host SError... We would rather leave the SError pending and let the
    host take it once we exit world-switch. To do this, we need to defer
    guest-entry if an SError is pending.
    
    Read the ISR to see if SError (or an IRQ) is pending. If so fake an
    exit. Place this check between __guest_enter()'s save of the host
    registers, and restore of the guest's. SError that occur between
    here and the eret into the guest must have affected the guest's
    registers, which we can naturally attribute to the guest.
    
    The dsb is needed to ensure any previous writes have been done before
    we read ISR_EL1. On systems without the v8.2 RAS extensions this
    doesn't give us anything as we can't contain errors, and the ESR bits
    to describe the severity are all implementation-defined. Replace
    this with a nop for these systems.
    Signed-off-by: default avatarJames Morse <james.morse@arm.com>
    Signed-off-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
    5dcd0fdb
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