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Commit 72a9b186 authored by KarimAllah Ahmed's avatar KarimAllah Ahmed Committed by David Vrabel
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xen: Remove event channel notification through Xen PCI platform device 



Ever since commit 254d1a3f ("xen/pv-on-hvm kexec: shutdown watches
from old kernel") using the INTx interrupt from Xen PCI platform
device for event channel notification would just lockup the guest
during bootup.  postcore_initcall now calls xs_reset_watches which
will eventually try to read a value from XenStore and will get stuck
on read_reply at XenBus forever since the platform driver is not
probed yet and its INTx interrupt handler is not registered yet. That
means that the guest can not be notified at this moment of any pending
event channels and none of the per-event handlers will ever be invoked
(including the XenStore one) and the reply will never be picked up by
the kernel.

The exact stack where things get stuck during xenbus_init:

-xenbus_init
 -xs_init
  -xs_reset_watches
   -xenbus_scanf
    -xenbus_read
     -xs_single
      -xs_single
       -xs_talkv

Vector callbacks have always been the favourite event notification
mechanism since their introduction in commit 38e20b07 ("x86/xen:
event channels delivery on HVM.") and the vector callback feature has
always been advertised for quite some time by Xen that's why INTx was
broken for several years now without impacting anyone.

Luckily this also means that event channel notification through INTx
is basically dead-code which can be safely removed without impacting
anybody since it has been effectively disabled for more than 4 years
with nobody complaining about it (at least as far as I'm aware of).

This commit removes event channel notification through Xen PCI
platform device.

Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: Julien Grall <julien.grall@citrix.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Ross Lagerwall <ross.lagerwall@citrix.com>
Cc: xen-devel@lists.xenproject.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-pci@vger.kernel.org
Cc: Anthony Liguori <aliguori@amazon.com>
Signed-off-by: default avatarKarimAllah Ahmed <karahmed@amazon.de>
Reviewed-by: default avatarBoris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: default avatarDavid Vrabel <david.vrabel@citrix.com>
parent c8761e20

arch/x86/include/asm/xen/events.h

+0 −11
Original line number Diff line number Diff line
@@ -20,15 +20,4 @@ static inline int xen_irqs_disabled(struct pt_regs *regs) 
/* No need for a barrier -- XCHG is a barrier on x86. */

#define xchg_xen_ulong(ptr, val) xchg((ptr), (val))



extern int xen_have_vector_callback;



/*

 * Events delivered via platform PCI interrupts are always

 * routed to vcpu 0 and hence cannot be rebound.

 */

static inline bool xen_support_evtchn_rebind(void)

{

	return (!xen_hvm_domain() || xen_have_vector_callback);

}



#endif /* _ASM_X86_XEN_EVENTS_H */

arch/x86/pci/xen.c

+1 −1
Original line number Diff line number Diff line
@@ -456,7 +456,7 @@ void __init xen_msi_init(void) 


int __init pci_xen_hvm_init(void)

{

	if (!xen_have_vector_callback || !xen_feature(XENFEAT_hvm_pirqs))

	if (!xen_feature(XENFEAT_hvm_pirqs))

		return 0;



#ifdef CONFIG_ACPI

arch/x86/xen/enlighten.c

+6 −15
Original line number Diff line number Diff line
@@ -137,8 +137,6 @@ struct shared_info xen_dummy_shared_info; 
void *xen_initial_gdt;



RESERVE_BRK(shared_info_page_brk, PAGE_SIZE);

__read_mostly int xen_have_vector_callback;

EXPORT_SYMBOL_GPL(xen_have_vector_callback);



static int xen_cpu_up_prepare(unsigned int cpu);

static int xen_cpu_up_online(unsigned int cpu);
@@ -1524,10 +1522,7 @@ static void __init xen_pvh_early_guest_init(void) 
	if (!xen_feature(XENFEAT_auto_translated_physmap))

		return;



	if (!xen_feature(XENFEAT_hvm_callback_vector))

		return;



	xen_have_vector_callback = 1;

	BUG_ON(!xen_feature(XENFEAT_hvm_callback_vector));



	xen_pvh_early_cpu_init(0, false);

	xen_pvh_set_cr_flags(0);
@@ -1864,9 +1859,7 @@ static int xen_cpu_up_prepare(unsigned int cpu) 
		xen_vcpu_setup(cpu);

	}



	if (xen_pv_domain() ||

	    (xen_have_vector_callback &&

	     xen_feature(XENFEAT_hvm_safe_pvclock)))

	if (xen_pv_domain() || xen_feature(XENFEAT_hvm_safe_pvclock))

		xen_setup_timer(cpu);



	rc = xen_smp_intr_init(cpu);
@@ -1882,9 +1875,7 @@ static int xen_cpu_dead(unsigned int cpu) 
{

	xen_smp_intr_free(cpu);



	if (xen_pv_domain() ||

	    (xen_have_vector_callback &&

	     xen_feature(XENFEAT_hvm_safe_pvclock)))

	if (xen_pv_domain() || xen_feature(XENFEAT_hvm_safe_pvclock))

		xen_teardown_timer(cpu);



	return 0;
@@ -1922,8 +1913,8 @@ static void __init xen_hvm_guest_init(void) 


	xen_panic_handler_init();



	if (xen_feature(XENFEAT_hvm_callback_vector))

		xen_have_vector_callback = 1;

	BUG_ON(!xen_feature(XENFEAT_hvm_callback_vector));



	xen_hvm_smp_init();

	WARN_ON(xen_cpuhp_setup());

	xen_unplug_emulated_devices();
@@ -1961,7 +1952,7 @@ bool xen_hvm_need_lapic(void) 
		return false;

	if (!xen_hvm_domain())

		return false;

	if (xen_feature(XENFEAT_hvm_pirqs) && xen_have_vector_callback)

	if (xen_feature(XENFEAT_hvm_pirqs))

		return false;

	return true;

}

arch/x86/xen/smp.c

+0 −2
Original line number Diff line number Diff line
@@ -765,8 +765,6 @@ static void __init xen_hvm_smp_prepare_cpus(unsigned int max_cpus) 


void __init xen_hvm_smp_init(void)

{

	if (!xen_have_vector_callback)

		return;

	smp_ops.smp_prepare_cpus = xen_hvm_smp_prepare_cpus;

	smp_ops.smp_send_reschedule = xen_smp_send_reschedule;

	smp_ops.cpu_die = xen_cpu_die;

arch/x86/xen/time.c

+0 −5
Original line number Diff line number Diff line
@@ -432,11 +432,6 @@ static void xen_hvm_setup_cpu_clockevents(void) 


void __init xen_hvm_init_time_ops(void)

{

	/* vector callback is needed otherwise we cannot receive interrupts

	 * on cpu > 0 and at this point we don't know how many cpus are

	 * available */

	if (!xen_have_vector_callback)

		return;

	if (!xen_feature(XENFEAT_hvm_safe_pvclock)) {

		printk(KERN_INFO "Xen doesn't support pvclock on HVM,"

				"disable pv timer\n");