• David Vrabel's avatar
    x86/xen: allow privcmd hypercalls to be preempted · fdfd811d
    David Vrabel authored
    Hypercalls submitted by user space tools via the privcmd driver can
    take a long time (potentially many 10s of seconds) if the hypercall
    has many sub-operations.
    
    A fully preemptible kernel may deschedule such as task in any upcall
    called from a hypercall continuation.
    
    However, in a kernel with voluntary or no preemption, hypercall
    continuations in Xen allow event handlers to be run but the task
    issuing the hypercall will not be descheduled until the hypercall is
    complete and the ioctl returns to user space.  These long running
    tasks may also trigger the kernel's soft lockup detection.
    
    Add xen_preemptible_hcall_begin() and xen_preemptible_hcall_end() to
    bracket hypercalls that may be preempted.  Use these in the privcmd
    driver.
    
    When returning from an upcall, call xen_maybe_preempt_hcall() which
    adds a schedule point if if the current task was within a preemptible
    hypercall.
    
    Since _cond_resched() can move the task to a different CPU, clear and
    set xen_in_preemptible_hcall around the call.
    Signed-off-by: default avatarDavid Vrabel <david.vrabel@citrix.com>
    Reviewed-by: default avatarBoris Ostrovsky <boris.ostrovsky@oracle.com>
    fdfd811d
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