xen: Remove event channel notification through Xen PCI platform device
authorKarimAllah Ahmed <karahmed@amazon.de>
Fri, 26 Aug 2016 21:55:36 +0000 (23:55 +0200)
committerDavid Vrabel <david.vrabel@citrix.com>
Fri, 30 Sep 2016 10:44:34 +0000 (11:44 +0100)
Ever since commit 254d1a3f02eb ("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 38e20b07efd5 ("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: KarimAllah Ahmed <karahmed@amazon.de>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
arch/x86/include/asm/xen/events.h
arch/x86/pci/xen.c
arch/x86/xen/enlighten.c
arch/x86/xen/smp.c
arch/x86/xen/time.c
drivers/xen/events/events_base.c
drivers/xen/platform-pci.c
include/xen/xen.h

index e6911caf5bbf16ddc46430c44fcd4186258b713c..608a79d5a4669ebf3a9060f895d0f5f03ab3286c 100644 (file)
@@ -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 */
index 3a483cb5ac817495be26b4b274c377b2774c347e..bedfab98077a219bd1d9842a0dc6e66f4b6a27c5 100644 (file)
@@ -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
index a9ba14ac3aeae3b6799dfa275aff57b2ca004c19..366b6aed4a8ee9ce499898b91724a1bf6f65e40e 100644 (file)
@@ -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;
 }
index 137afbbd05903baa700d9cce5d9707fac07f0062..311acad7dad2abdc8501c70866674ed4f5858495 100644 (file)
@@ -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;
index 67356d29d74d033f07ede538eb14fe8cefcc056a..33d8f6a7829d75c6673a8287d8a9d4be68401d9e 100644 (file)
@@ -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");
index d5dbdb9d24d8dc264ec2b0927833c5c7d9997dfd..9ecfcdcdd6d60afadb4adae79d7cbeace70f40d1 100644 (file)
@@ -1314,9 +1314,6 @@ static int rebind_irq_to_cpu(unsigned irq, unsigned tcpu)
        if (!VALID_EVTCHN(evtchn))
                return -1;
 
-       if (!xen_support_evtchn_rebind())
-               return -1;
-
        /* Send future instances of this interrupt to other vcpu. */
        bind_vcpu.port = evtchn;
        bind_vcpu.vcpu = xen_vcpu_nr(tcpu);
@@ -1650,20 +1647,15 @@ void xen_callback_vector(void)
 {
        int rc;
        uint64_t callback_via;
-       if (xen_have_vector_callback) {
-               callback_via = HVM_CALLBACK_VECTOR(HYPERVISOR_CALLBACK_VECTOR);
-               rc = xen_set_callback_via(callback_via);
-               if (rc) {
-                       pr_err("Request for Xen HVM callback vector failed\n");
-                       xen_have_vector_callback = 0;
-                       return;
-               }
-               pr_info("Xen HVM callback vector for event delivery is enabled\n");
-               /* in the restore case the vector has already been allocated */
-               if (!test_bit(HYPERVISOR_CALLBACK_VECTOR, used_vectors))
-                       alloc_intr_gate(HYPERVISOR_CALLBACK_VECTOR,
-                                       xen_hvm_callback_vector);
-       }
+
+       callback_via = HVM_CALLBACK_VECTOR(HYPERVISOR_CALLBACK_VECTOR);
+       rc = xen_set_callback_via(callback_via);
+       BUG_ON(rc);
+       pr_info("Xen HVM callback vector for event delivery is enabled\n");
+       /* in the restore case the vector has already been allocated */
+       if (!test_bit(HYPERVISOR_CALLBACK_VECTOR, used_vectors))
+               alloc_intr_gate(HYPERVISOR_CALLBACK_VECTOR,
+                               xen_hvm_callback_vector);
 }
 #else
 void xen_callback_vector(void) {}
index cf9666680c8c0e57225047939d169228724a7ab6..b59c9455aae1d79753fd4bd9aca72cc1e6ae40a5 100644 (file)
@@ -42,7 +42,6 @@
 static unsigned long platform_mmio;
 static unsigned long platform_mmio_alloc;
 static unsigned long platform_mmiolen;
-static uint64_t callback_via;
 
 static unsigned long alloc_xen_mmio(unsigned long len)
 {
@@ -55,51 +54,6 @@ static unsigned long alloc_xen_mmio(unsigned long len)
        return addr;
 }
 
-static uint64_t get_callback_via(struct pci_dev *pdev)
-{
-       u8 pin;
-       int irq;
-
-       irq = pdev->irq;
-       if (irq < 16)
-               return irq; /* ISA IRQ */
-
-       pin = pdev->pin;
-
-       /* We don't know the GSI. Specify the PCI INTx line instead. */
-       return ((uint64_t)0x01 << 56) | /* PCI INTx identifier */
-               ((uint64_t)pci_domain_nr(pdev->bus) << 32) |
-               ((uint64_t)pdev->bus->number << 16) |
-               ((uint64_t)(pdev->devfn & 0xff) << 8) |
-               ((uint64_t)(pin - 1) & 3);
-}
-
-static irqreturn_t do_hvm_evtchn_intr(int irq, void *dev_id)
-{
-       xen_hvm_evtchn_do_upcall();
-       return IRQ_HANDLED;
-}
-
-static int xen_allocate_irq(struct pci_dev *pdev)
-{
-       return request_irq(pdev->irq, do_hvm_evtchn_intr,
-                       IRQF_NOBALANCING | IRQF_TRIGGER_RISING,
-                       "xen-platform-pci", pdev);
-}
-
-static int platform_pci_resume(struct pci_dev *pdev)
-{
-       int err;
-       if (xen_have_vector_callback)
-               return 0;
-       err = xen_set_callback_via(callback_via);
-       if (err) {
-               dev_err(&pdev->dev, "platform_pci_resume failure!\n");
-               return err;
-       }
-       return 0;
-}
-
 static int platform_pci_probe(struct pci_dev *pdev,
                              const struct pci_device_id *ent)
 {
@@ -138,21 +92,6 @@ static int platform_pci_probe(struct pci_dev *pdev,
        platform_mmio = mmio_addr;
        platform_mmiolen = mmio_len;
 
-       if (!xen_have_vector_callback) {
-               ret = xen_allocate_irq(pdev);
-               if (ret) {
-                       dev_warn(&pdev->dev, "request_irq failed err=%d\n", ret);
-                       goto out;
-               }
-               callback_via = get_callback_via(pdev);
-               ret = xen_set_callback_via(callback_via);
-               if (ret) {
-                       dev_warn(&pdev->dev, "Unable to set the evtchn callback "
-                                        "err=%d\n", ret);
-                       goto out;
-               }
-       }
-
        max_nr_gframes = gnttab_max_grant_frames();
        grant_frames = alloc_xen_mmio(PAGE_SIZE * max_nr_gframes);
        ret = gnttab_setup_auto_xlat_frames(grant_frames);
@@ -184,9 +123,6 @@ static struct pci_driver platform_driver = {
        .name =           DRV_NAME,
        .probe =          platform_pci_probe,
        .id_table =       platform_pci_tbl,
-#ifdef CONFIG_PM
-       .resume_early =   platform_pci_resume,
-#endif
 };
 
 static int __init platform_pci_init(void)
index 0c0e3ef4c45dcfe7767af8c7f9d5ae2309e4efdc..f0f0252cff9aab2442e8df64430ec118a2f391aa 100644 (file)
@@ -38,8 +38,7 @@ extern enum xen_domain_type xen_domain_type;
  */
 #include <xen/features.h>
 #define xen_pvh_domain() (xen_pv_domain() && \
-                         xen_feature(XENFEAT_auto_translated_physmap) && \
-                         xen_have_vector_callback)
+                         xen_feature(XENFEAT_auto_translated_physmap))
 #else
 #define xen_pvh_domain()       (0)
 #endif