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    Subject[PATCH 04/10] xen: add batch completion callbacks
    This adds a mechanism to register a callback function to be called once
    a batch of hypercalls has been issued. This is typically used to unlock
    things which must remain locked until the hypercall has taken place.

    [ Stable folks: pre-req for 2.6.23 bugfix "xen: deal with stale cr3
    values when unpinning pagetables" ]

    Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
    Cc: Stable Kernel <stable@kernel.org>

    ---
    arch/i386/xen/multicalls.c | 29 ++++++++++++++++++++++++++---
    arch/i386/xen/multicalls.h | 3 +++
    2 files changed, 29 insertions(+), 3 deletions(-)

    ===================================================================
    --- a/arch/i386/xen/multicalls.c
    +++ b/arch/i386/xen/multicalls.c
    @@ -32,7 +32,11 @@ struct mc_buffer {
    struct mc_buffer {
    struct multicall_entry entries[MC_BATCH];
    u64 args[MC_ARGS];
    - unsigned mcidx, argidx;
    + struct callback {
    + void (*fn)(void *);
    + void *data;
    + } callbacks[MC_BATCH];
    + unsigned mcidx, argidx, cbidx;
    };

    static DEFINE_PER_CPU(struct mc_buffer, mc_buffer);
    @@ -43,6 +47,7 @@ void xen_mc_flush(void)
    struct mc_buffer *b = &__get_cpu_var(mc_buffer);
    int ret = 0;
    unsigned long flags;
    + int i;

    BUG_ON(preemptible());

    @@ -51,8 +56,6 @@ void xen_mc_flush(void)
    local_irq_save(flags);

    if (b->mcidx) {
    - int i;
    -
    if (HYPERVISOR_multicall(b->entries, b->mcidx) != 0)
    BUG();
    for (i = 0; i < b->mcidx; i++)
    @@ -64,6 +67,13 @@ void xen_mc_flush(void)
    BUG_ON(b->argidx != 0);

    local_irq_restore(flags);
    +
    + for(i = 0; i < b->cbidx; i++) {
    + struct callback *cb = &b->callbacks[i];
    +
    + (*cb->fn)(cb->data);
    + }
    + b->cbidx = 0;

    BUG_ON(ret);
    }
    @@ -88,3 +98,16 @@ struct multicall_space __xen_mc_entry(si

    return ret;
    }
    +
    +void xen_mc_callback(void (*fn)(void *), void *data)
    +{
    + struct mc_buffer *b = &__get_cpu_var(mc_buffer);
    + struct callback *cb;
    +
    + if (b->cbidx == MC_BATCH)
    + xen_mc_flush();
    +
    + cb = &b->callbacks[b->cbidx++];
    + cb->fn = fn;
    + cb->data = data;
    +}
    ===================================================================
    --- a/arch/i386/xen/multicalls.h
    +++ b/arch/i386/xen/multicalls.h
    @@ -42,4 +42,7 @@ static inline void xen_mc_issue(unsigned
    local_irq_restore(x86_read_percpu(xen_mc_irq_flags));
    }

    +/* Set up a callback to be called when the current batch is flushed */
    +void xen_mc_callback(void (*fn)(void *), void *data);
    +
    #endif /* _XEN_MULTICALLS_H */
    --

    -
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