Re: [Xen-devel] [PATCH 7 of 7] KEXEC: correctly revert x2apic state when kexecing

[Keir Fraser <keir@xxxxxxx>]

On 13/06/2011 18:02, "Andrew Cooper" <andrew.cooper3@xxxxxxxxxx> wrote:

> Introduce the boolean variable 'kexecing' which indicates to functions
> whether we are on the kexec path or not.  This is used by
> disable_local_APIC() to try and revert the APIC mode back to how it
> was found on boot.

Does this need to be done only on the kexec path, rather than
unconditionally in disable_local_APIC()?

 -- Keir

> We also need some fudging of the x2apic_enabled variable.  It is used
> in multiple places over the codebase to mean multiple things,
> including:
>     What did the user specifify on the command line?
>     Did the BIOS boot me in x2apic mode?
>     Is the BSP Local APIC in x2apic mode?
>     What mode is my Local APIC in?
> 
> Therefore, set it up to prevent a protection fault when disabling the
> IOAPICs.  (In this case, it is used in the "What mode is my Local APIC
> in?" case, so the processor doesnt suffer a protection fault because
> of trying to use x2apic MSRs when it should be using xapic MMIO)
> 
> Finally, make sure that interrupts are disabled when jumping into the
> purgatory code.  It would be bad to service interrupts in the Xen
> context when the next kernel is booting.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> 
> diff -r 3ad737eb0a8d -r b6666fbafe33 xen/arch/x86/apic.c
> --- a/xen/arch/x86/apic.c Mon Jun 13 17:45:43 2011 +0100
> +++ b/xen/arch/x86/apic.c Mon Jun 13 17:45:43 2011 +0100
> @@ -37,6 +37,7 @@
>  #include <asm/asm_defns.h> /* for BUILD_SMP_INTERRUPT */
>  #include <mach_apic.h>
>  #include <io_ports.h>
> +#include <xen/kexec.h>
>  
>  static bool_t tdt_enabled __read_mostly;
>  static bool_t tdt_enable __initdata = 1;
> @@ -345,6 +346,33 @@ void disable_local_APIC(void)
>          wrmsrl(MSR_IA32_APICBASE, msr_content &
>                 ~(MSR_IA32_APICBASE_ENABLE|MSR_IA32_APICBASE_EXTD));
>      }
> +
> +    if ( kexecing )
> +    {
> +        uint64_t msr_content;
> +        rdmsrl(MSR_IA32_APICBASE, msr_content);
> +        msr_content &= ~(MSR_IA32_APICBASE_ENABLE|MSR_IA32_APICBASE_EXTD);
> +        wrmsrl(MSR_IA32_APICBASE, msr_content);
> +
> +        switch ( apic_boot_mode )
> +        {
> +        case APIC_MODE_DISABLED:
> +            break; /* Nothing to do - we did this above */
> +        case APIC_MODE_XAPIC:
> +            msr_content |= MSR_IA32_APICBASE_ENABLE;
> +            wrmsrl(MSR_IA32_APICBASE, msr_content);
> +            break;
> +        case APIC_MODE_X2APIC:
> +            msr_content |= (MSR_IA32_APICBASE_ENABLE|MSR_IA32_APICBASE_EXTD);
> +            wrmsrl(MSR_IA32_APICBASE, msr_content);
> +            break;
> +        default:
> +            printk("Default case when reverting #%d lapic to boot state\n",
> +                   smp_processor_id());
> +            break;
> +        }
> +    }
> +
>  }
>  
>  /*
> diff -r 3ad737eb0a8d -r b6666fbafe33 xen/arch/x86/crash.c
> --- a/xen/arch/x86/crash.c Mon Jun 13 17:45:43 2011 +0100
> +++ b/xen/arch/x86/crash.c Mon Jun 13 17:45:43 2011 +0100
> @@ -27,6 +27,7 @@
>  #include <asm/hvm/support.h>
>  #include <asm/apic.h>
>  #include <asm/io_apic.h>
> +#include <xen/iommu.h>
>  
>  static atomic_t waiting_for_crash_ipi;
>  static unsigned int crashing_cpu;
> @@ -82,6 +83,15 @@ static void nmi_shootdown_cpus(void)
>      iommu_crash_shutdown();
>  
>      __stop_this_cpu();
> +
> +    /* This is a bit of a hack due to the problems with the x2apic_enabled
> +     * variable, but we can't do any better without a significant refactoring
> +     * of the APIC code */
> +    if ( current_local_apic_mode() == APIC_MODE_X2APIC )
> +        x2apic_enabled = 1;
> +    else
> +        x2apic_enabled = 0;
> +
>      disable_IO_APIC();
>  
>      local_irq_restore(flags);
> diff -r 3ad737eb0a8d -r b6666fbafe33 xen/arch/x86/machine_kexec.c
> --- a/xen/arch/x86/machine_kexec.c Mon Jun 13 17:45:43 2011 +0100
> +++ b/xen/arch/x86/machine_kexec.c Mon Jun 13 17:45:43 2011 +0100
> @@ -91,6 +91,11 @@ void machine_kexec(xen_kexec_image_t *im
>      if ( hpet_broadcast_is_available() )
>          hpet_disable_legacy_broadcast();
>  
> +    /* We are about to permenantly jump out of the Xen context into the kexec
> +     * purgatory code.  We really dont want to be still servicing interupts.
> +     */
> +    local_irq_disable();
> +
>      /*
>       * compat_machine_kexec() returns to idle pagetables, which requires us
>       * to be running on a static GDT mapping (idle pagetables have no GDT
> diff -r 3ad737eb0a8d -r b6666fbafe33 xen/common/kexec.c
> --- a/xen/common/kexec.c Mon Jun 13 17:45:43 2011 +0100
> +++ b/xen/common/kexec.c Mon Jun 13 17:45:43 2011 +0100
> @@ -29,6 +29,8 @@
>  #include <compat/kexec.h>
>  #endif
>  
> +bool_t kexecing = FALSE;
> +
>  static DEFINE_PER_CPU_READ_MOSTLY(void *, crash_notes);
>  
>  static Elf_Note *xen_crash_note;
> @@ -220,6 +222,8 @@ void kexec_crash(void)
>      if ( !test_bit(KEXEC_IMAGE_CRASH_BASE + pos, &kexec_flags) )
>          return;
>  
> +    kexecing = TRUE;
> +
>      kexec_common_shutdown();
>      kexec_crash_save_cpu();
>      machine_crash_shutdown();
> @@ -232,6 +236,8 @@ static long kexec_reboot(void *_image)
>  {
>      xen_kexec_image_t *image = _image;
>  
> +    kexecing = TRUE;
> +
>      kexec_common_shutdown();
>      machine_reboot_kexec(image);
>  
> diff -r 3ad737eb0a8d -r b6666fbafe33 xen/include/xen/kexec.h
> --- a/xen/include/xen/kexec.h Mon Jun 13 17:45:43 2011 +0100
> +++ b/xen/include/xen/kexec.h Mon Jun 13 17:45:43 2011 +0100
> @@ -12,6 +12,8 @@ typedef struct xen_kexec_reserve {
>  
>  extern xen_kexec_reserve_t kexec_crash_area;
>  
> +extern bool_t kexecing;
> +
>  void set_kexec_crash_area_size(u64 system_ram);
>  
>  /* We have space for 4 images to support atomic update
> 
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