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Re: [Xen-devel] [PATCH v2] xen/events: Always allocate legacy interrupts on PV guests

On 11/20/2015 06:24 AM, Stefano Stabellini wrote:
On Wed, 18 Nov 2015, Boris Ostrovsky wrote:
After commit 8c058b0b9c34 ("x86/irq: Probe for PIC presence before
allocating descs for legacy IRQs") early_irq_init() will no longer
preallocate descriptors for legacy interrupts if PIC does not
exist, which is the case for Xen PV guests.

Therefore we may need to allocate those descriptors ourselves.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
You need to do this for arm64 too.

FYI you can download arm64 cross-compilers from
then you can use them by exporting ARCH=arm64 and

I did test on arm but didn't realize that arm64 uses different include files.

Does arm64 not have any legacy interrupts?

BTW, I got this build error:

  STUBCPY drivers/firmware/efi/libstub/lib-sort.stub.o
0000000000000000 R_AARCH64_ABS64   __efistub_sort
0000000000000008 R_AARCH64_ABS64   .init__ksymtab_strings
drivers/firmware/efi/libstub/lib-sort.stub.o: absolute symbol references not allowed in the EFI stub drivers/firmware/efi/libstub/Makefile:63: recipe for target 'drivers/firmware/efi/libstub/lib-sort.stub.o' failed
make[4]: *** [drivers/firmware/efi/libstub/lib-sort.stub.o] Error 1
scripts/Makefile.build:403: recipe for target 'drivers/firmware/efi/libstub' failed
make[3]: *** [drivers/firmware/efi/libstub] Error 2
scripts/Makefile.build:403: recipe for target 'drivers/firmware/efi' failed
make[2]: *** [drivers/firmware/efi] Error 2
scripts/Makefile.build:403: recipe for target 'drivers/firmware' failed
make[1]: *** [drivers/firmware] Error 2
Makefile:943: recipe for target 'drivers' failed
make: *** [drivers] Error 2

I worked around this by removing some of EFI config options but presumably this needs to be properly fixed.


v2: Use nr_legacy_irqs() instead of NR_IRQS_LEGACY (needs definition for ARM)

  arch/arm/include/asm/irq.h       | 4 ++++
  drivers/xen/events/events_base.c | 5 +++--
  2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/arm/include/asm/irq.h b/arch/arm/include/asm/irq.h
index be1d07d..b864f60 100644
--- a/arch/arm/include/asm/irq.h
+++ b/arch/arm/include/asm/irq.h
@@ -2,6 +2,10 @@
  #define __ASM_ARM_IRQ_H
#define NR_IRQS_LEGACY 16
+static inline int nr_legacy_irqs(void)
+       return NR_IRQS_LEGACY;
  #include <mach/irqs.h>
diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
index 849500e..524c221 100644
--- a/drivers/xen/events/events_base.c
+++ b/drivers/xen/events/events_base.c
@@ -39,6 +39,7 @@
  #include <asm/irq.h>
  #include <asm/idle.h>
  #include <asm/io_apic.h>
+#include <asm/i8259.h>
  #include <asm/xen/pci.h>
  #include <asm/sync_bitops.h>
@@ -420,7 +421,7 @@ static int __must_check xen_allocate_irq_gsi(unsigned gsi)
                return xen_allocate_irq_dynamic();
/* Legacy IRQ descriptors are already allocated by the arch. */
-       if (gsi < NR_IRQS_LEGACY)
+       if (gsi < nr_legacy_irqs())
                irq = gsi;
                irq = irq_alloc_desc_at(gsi, -1);
@@ -446,7 +447,7 @@ static void xen_free_irq(unsigned irq)
/* Legacy IRQ descriptors are managed by the arch. */
-       if (irq < NR_IRQS_LEGACY)
+       if (irq < nr_legacy_irqs())

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