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    Subject[RFC PATCH] xen: get correct nr_irqs_gsi value from hypervisor
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    nr_irqs_gsi is set in probe_nr_irqs_gsi()
    nr_irqs_gsi = gsi_top + NR_IRQS_LEGACY;

    gsi_top is set in mp_register_ioapic()
    gsi_top = gsi_cfg->gsi_end + 1;

    mp_register_ioapic() calls io_apic_read, which don't have a Xen specific
    version. Actually, io_apic_read() always return -1 on Xen Dom0 kernel.

    So currently, nr_irqs_gsi is always wrong on Xen Dom0 kernel.

    This patch gets the correct nr_irqs_gsi value from Xen hypervisor with a
    hypercall.

    Signed-off-by: Lin Ming <mlin@ss.pku.edu.cn>
    --
    arch/x86/include/asm/io_apic.h | 2 ++
    arch/x86/kernel/apic/io_apic.c | 2 +-
    arch/x86/xen/setup.c | 9 +++++++++
    include/xen/interface/physdev.h | 6 ++++++
    4 files changed, 18 insertions(+), 1 deletions(-)

    (I will send xen hypervisor patch in another mail)

    Here comes the detail story.

    Xen Dom0 kernel panics with 3.4-rc1. I took the panics picture at
    http://www.sendspace.com/file/12ob33

    Bisected to below commit.

    commit 73d63d038ee9f769f5e5b46792d227fe20e442c5
    Author: Suresh Siddha <suresh.b.siddha@intel.com>
    Date: Mon Mar 12 11:36:33 2012 -0700

    x86/ioapic: Add register level checks to detect bogus io-apic entries

    But this commit itself has no problem.
    This commit just triggers the panic.

    The panic happens at xen_irq_init(..)

    pci_enable_device
    __pci_enable_device_flags
    do_pci_enable_device
    pcibios_enable_device
    acpi_pci_irq_enable
    acpi_register_gsi
    acpi_register_gsi_xen
    xen_register_gsi
    xen_register_pirq
    xen_bind_pirq_gsi_to_irq
    xen_allocate_irq_gsi:
    irq = irq_alloc_desc_at(gsi, -1);
    xen_irq_init(irq);

    On my machine, when enable PCI root port, gsi 16 is passed into
    irq_alloc_desc_at, but it returns -17(-EEXIST) because irq 16 was
    already took by xen timer(see below). Then negative value -17 is passed
    into xen_irq_init --> irq_to_desc --> radix_tree_lookup, which causes
    the panic.

    xen timer allocates the irq number "nr_irqs_gsi"
    nr_irqs_gsi is set in probe_nr_irqs_gsi()
    nr_irqs_gsi = gsi_top + NR_IRQS_LEGACY
    gsi_top is set in mp_register_ioapic()
    gsi_top = gsi_cfg->gsi_end + 1;

    In 3.4-rc1 kernel:

    mp_register_ioapic
    bad_ioapic_register (added in 3.4-rc1)
    <always return true(bad) on Xen Dom0 kernel>

    So mp_register_ioapic exist and gsi_top was not set up. It is left as
    the initialized value(zero). So nr_irqs_gsi is 16(NR_IRQS_LEGACY).
    That's why Xen timer allocated irq 16.


    Actually, gsi_top was never setup correctly in mp_register_ioapic on Xen
    Dom0 kernel. Because mp_register_ioapic calls io_apic_read, which is not
    implemented with hypercall in Linux kernel. So io_apic_read() always
    return -1 on Xen Dom0 kernel.

    For 3.3 kernel in Xen Dom0, the dmesg shows

    IOAPIC[0]: apic_id 2, version 255, address 0xfec00000, GSI 0-255
    ......
    nr_irqs_gsi: 272

    This is obviously wrong, "255" is actually -1(0xFFFF).


    diff --git a/arch/x86/include/asm/io_apic.h b/arch/x86/include/asm/io_apic.h
    index 2c4943d..a8bf3b2 100644
    --- a/arch/x86/include/asm/io_apic.h
    +++ b/arch/x86/include/asm/io_apic.h
    @@ -115,6 +115,8 @@ struct IR_IO_APIC_route_entry {
    */
    extern int nr_ioapics;

    +extern int nr_irqs_gsi;
    +
    extern int mpc_ioapic_id(int ioapic);
    extern unsigned int mpc_ioapic_addr(int ioapic);
    extern struct mp_ioapic_gsi *mp_ioapic_gsi_routing(int ioapic);
    diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
    index e88300d..8bff292 100644
    --- a/arch/x86/kernel/apic/io_apic.c
    +++ b/arch/x86/kernel/apic/io_apic.c
    @@ -140,7 +140,7 @@ struct mpc_intsrc mp_irqs[MAX_IRQ_SOURCES];
    int mp_irq_entries;

    /* GSI interrupts */
    -static int nr_irqs_gsi = NR_IRQS_LEGACY;
    +int nr_irqs_gsi = NR_IRQS_LEGACY;

    #if defined (CONFIG_MCA) || defined (CONFIG_EISA)
    int mp_bus_id_to_type[MAX_MP_BUSSES];
    diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
    index 1ba8dff..9ce82bc 100644
    --- a/arch/x86/xen/setup.c
    +++ b/arch/x86/xen/setup.c
    @@ -389,6 +389,9 @@ void __cpuinit xen_enable_syscall(void)

    void __init xen_arch_setup(void)
    {
    + struct physdev_nr_irqs_gsi irqs_gsi;
    + int rc;
    +
    xen_panic_handler_init();

    HYPERVISOR_vm_assist(VMASST_CMD_enable, VMASST_TYPE_4gb_segments);
    @@ -424,4 +427,10 @@ void __init xen_arch_setup(void)
    disable_cpufreq();
    WARN_ON(set_pm_idle_to_default());
    fiddle_vdso();
    +
    + rc = HYPERVISOR_physdev_op(PHYSDEVOP_nr_irqs_gsi, &irqs_gsi);
    + if (rc)
    + printk(KERN_ERR "Failed to init nr_irqs_gsi, err_code:%d\n", rc);
    + else
    + nr_irqs_gsi = irqs_gsi.nr_irqs_gsi;
    }
    diff --git a/include/xen/interface/physdev.h b/include/xen/interface/physdev.h
    index 9ce788d..180a0a3 100644
    --- a/include/xen/interface/physdev.h
    +++ b/include/xen/interface/physdev.h
    @@ -258,6 +258,12 @@ struct physdev_pci_device {
    uint8_t devfn;
    };

    +#define PHYSDEVOP_nr_irqs_gsi 29
    +struct physdev_nr_irqs_gsi {
    + /* OUT */
    + uint32_t nr_irqs_gsi;
    +};
    +
    /*
    * Notify that some PIRQ-bound event channels have been unmasked.
    * ** This command is obsolete since interface version 0x00030202 and is **





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