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xen: Remove event channel notification through Xen PCI platform device

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Ever since commit 254d1a3f02 ("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 38e20b07ef ("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 <[email protected]>
Cc: David Vrabel <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: [email protected]
Cc: Konrad Rzeszutek Wilk <[email protected]>
Cc: Bjorn Helgaas <[email protected]>
Cc: Stefano Stabellini <[email protected]>
Cc: Julien Grall <[email protected]>
Cc: Vitaly Kuznetsov <[email protected]>
Cc: Paul Gortmaker <[email protected]>
Cc: Ross Lagerwall <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: Anthony Liguori <[email protected]>
Signed-off-by: KarimAllah Ahmed <[email protected]>
Reviewed-by: Boris Ostrovsky <[email protected]>
Signed-off-by: David Vrabel <[email protected]>
This commit is contained in:
KarimAllah Ahmed 2016-08-26 23:55:36 +02:00 • committed by David Vrabel
commit 72a9b18629
8 changed files with 17 additions and 117 deletions
Download patch file Download diff file Expand all files Collapse all files

26
drivers/xen/events/events_base.c
View 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) {}

64
drivers/xen/platform-pci.c
View 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)