Re: [Xen-devel] [PATCH V2] keep iommu disabled until iommu_setup() is called

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 22.10.12 at 00:22, Ronny Hegewald <ronny.hegewald@xxxxxxxxx> wrote:
> The iommu is enabled by default when xen is booting and later disabled in 
> iommu_setup() when no iommu is present.
> 
> But under some circumstances iommu-code can be called before iommu_setup() is 
> 
> processed. If there is no iommu available xen crashes.
> 
> This can happen for example when panic(...) is called that got introduced 
> with
> patch "x86-64: detect processors subject to AMD erratum #121 and refuse to 
> boot." since xen 4.1.3 and results in the following stacktrace:
> 
>    find_iommu_for_device
>    amd_iommu_ioapic_update_ire
>    timer_interrupt
>    enable_8259_A_irq
>    do_IRQ
>    printk_start_of_line
>    acpi_os_printf
>    io_apic_write
>    __ioapic_write_entry
>    ioapic_write_entry
>    __clear_IO_APIC_pin
>    clear_IO_APIC
>    disable_IO_APIC
>    __stop_this_cpu
>    smp_send_stop
>    machine_restart
>    panic
>    tasklet_schedule_on_cpu
>    display_cacheinfo
>    init_amd
>    generic_identify
>    identify_cpu
>    _start_xen
>    _high_start
> 
> 
> This patch fixes this by keeping the iommu disabled until iommu_setup() is 
> entered. 
> 
> Signed-off-by: Ronny Hegewald@xxxxxxxxx 
> 
> ---
> Changed since V1:
>    * simplify code as suggested by Jan Beulich

I'm completing that adjustment as originally requested. Plus, in
case you happen to send patches again in the future, please
prepare them against the -unstable tree, not some older version.

Jan

> --- xen/drivers/passthrough/iommu.c.org       2012-10-05 03:38:33.000000000 
> +0000
> +++ xen/drivers/passthrough/iommu.c   2012-10-21 21:07:37.000000000 +0000
> @@ -38,7 +38,8 @@
>   *   no-intremap                Disable VT-d Interrupt Remapping
>   */
>  custom_param("iommu", parse_iommu_param);
> -bool_t __read_mostly iommu_enabled = 1;
> +bool_t iommu_enable_default __initdata = 1;
> +bool_t __read_mostly iommu_enabled;
>  bool_t __read_mostly force_iommu;
>  bool_t __initdata iommu_dom0_strict;
>  bool_t __read_mostly iommu_verbose;
> @@ -61,7 +62,7 @@
>              *ss = '\0';
>  
>          if ( !parse_bool(s) )
> -            iommu_enabled = 0;
> +            iommu_enable_default = 0;
>          else if ( !strcmp(s, "force") || !strcmp(s, "required") )
>              force_iommu = 1;
>          else if ( !strcmp(s, "workaround_bios_bug") )
> @@ -316,7 +317,7 @@
>      if ( iommu_dom0_strict )
>          iommu_passthrough = 0;
>  
> -    if ( iommu_enabled )
> +    if ( iommu_enable_default )
>      {
>          rc = iommu_hardware_setup();
>          iommu_enabled = (rc == 0);
> 
> 
> 
> 
> _______________________________________________
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> Xen-devel@xxxxxxxxxxxxx 
> http://lists.xen.org/xen-devel 




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