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    Subject[PATCH v6 30/46] x86/xen: Use get/put_online_cpus_atomic() to prevent CPU offline
    Date
    Once stop_machine() is gone from the CPU offline path, we won't be able to
    depend on preempt_disable() or local_irq_disable() to prevent CPUs from
    going offline from under us.

    Use the get/put_online_cpus_atomic() APIs to prevent CPUs from going offline,
    while invoking from atomic context.

    Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
    Cc: Jeremy Fitzhardinge <jeremy@goop.org>
    Cc: "H. Peter Anvin" <hpa@zytor.com>
    Cc: x86@kernel.org
    Cc: xen-devel@lists.xensource.com
    Cc: virtualization@lists.linux-foundation.org
    Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
    ---

    arch/x86/xen/mmu.c | 11 +++++++++--
    arch/x86/xen/smp.c | 9 +++++++++
    2 files changed, 18 insertions(+), 2 deletions(-)

    diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
    index 01de35c..6a95a15 100644
    --- a/arch/x86/xen/mmu.c
    +++ b/arch/x86/xen/mmu.c
    @@ -39,6 +39,7 @@
    * Jeremy Fitzhardinge <jeremy@xensource.com>, XenSource Inc, 2007
    */
    #include <linux/sched.h>
    +#include <linux/cpu.h>
    #include <linux/highmem.h>
    #include <linux/debugfs.h>
    #include <linux/bug.h>
    @@ -1163,9 +1164,13 @@ static void xen_drop_mm_ref(struct mm_struct *mm)
    */
    static void xen_exit_mmap(struct mm_struct *mm)
    {
    - get_cpu(); /* make sure we don't move around */
    + /*
    + * Make sure we don't move around, and prevent CPUs from going
    + * offline.
    + */
    + get_online_cpus_atomic();
    xen_drop_mm_ref(mm);
    - put_cpu();
    + put_online_cpus_atomic();

    spin_lock(&mm->page_table_lock);

    @@ -1371,6 +1376,7 @@ static void xen_flush_tlb_others(const struct cpumask *cpus,
    args->op.arg2.vcpumask = to_cpumask(args->mask);

    /* Remove us, and any offline CPUS. */
    + get_online_cpus_atomic();
    cpumask_and(to_cpumask(args->mask), cpus, cpu_online_mask);
    cpumask_clear_cpu(smp_processor_id(), to_cpumask(args->mask));

    @@ -1383,6 +1389,7 @@ static void xen_flush_tlb_others(const struct cpumask *cpus,
    MULTI_mmuext_op(mcs.mc, &args->op, 1, NULL, DOMID_SELF);

    xen_mc_issue(PARAVIRT_LAZY_MMU);
    + put_online_cpus_atomic();
    }

    static unsigned long xen_read_cr3(void)
    diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
    index 34bc4ce..cb82e71 100644
    --- a/arch/x86/xen/smp.c
    +++ b/arch/x86/xen/smp.c
    @@ -16,6 +16,7 @@
    #include <linux/err.h>
    #include <linux/slab.h>
    #include <linux/smp.h>
    +#include <linux/cpu.h>
    #include <linux/irq_work.h>

    #include <asm/paravirt.h>
    @@ -480,8 +481,10 @@ static void __xen_send_IPI_mask(const struct cpumask *mask,
    {
    unsigned cpu;

    + get_online_cpus_atomic();
    for_each_cpu_and(cpu, mask, cpu_online_mask)
    xen_send_IPI_one(cpu, vector);
    + put_online_cpus_atomic();
    }

    static void xen_smp_send_call_function_ipi(const struct cpumask *mask)
    @@ -544,8 +547,10 @@ void xen_send_IPI_all(int vector)
    {
    int xen_vector = xen_map_vector(vector);

    + get_online_cpus_atomic();
    if (xen_vector >= 0)
    __xen_send_IPI_mask(cpu_online_mask, xen_vector);
    + put_online_cpus_atomic();
    }

    void xen_send_IPI_self(int vector)
    @@ -565,20 +570,24 @@ void xen_send_IPI_mask_allbutself(const struct cpumask *mask,
    if (!(num_online_cpus() > 1))
    return;

    + get_online_cpus_atomic();
    for_each_cpu_and(cpu, mask, cpu_online_mask) {
    if (this_cpu == cpu)
    continue;

    xen_smp_send_call_function_single_ipi(cpu);
    }
    + put_online_cpus_atomic();
    }

    void xen_send_IPI_allbutself(int vector)
    {
    int xen_vector = xen_map_vector(vector);

    + get_online_cpus_atomic();
    if (xen_vector >= 0)
    xen_send_IPI_mask_allbutself(cpu_online_mask, xen_vector);
    + put_online_cpus_atomic();
    }

    static irqreturn_t xen_call_function_interrupt(int irq, void *dev_id)


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