From 72a9b186292d98494f222226cfd24a1621796209 Mon Sep 17 00:00:00 2001 From: KarimAllah Ahmed Date: Fri, 26 Aug 2016 23:55:36 +0200 Subject: xen: Remove event channel notification through Xen PCI platform device 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 Cc: David Vrabel Cc: Juergen Gross Cc: Thomas Gleixner Cc: Ingo Molnar Cc: "H. Peter Anvin" Cc: x86@kernel.org Cc: Konrad Rzeszutek Wilk Cc: Bjorn Helgaas Cc: Stefano Stabellini Cc: Julien Grall Cc: Vitaly Kuznetsov Cc: Paul Gortmaker Cc: Ross Lagerwall Cc: xen-devel@lists.xenproject.org Cc: linux-kernel@vger.kernel.org Cc: linux-pci@vger.kernel.org Cc: Anthony Liguori Signed-off-by: KarimAllah Ahmed Reviewed-by: Boris Ostrovsky Signed-off-by: David Vrabel --- arch/x86/pci/xen.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch/x86/pci/xen.c') diff --git a/arch/x86/pci/xen.c b/arch/x86/pci/xen.c index 3a483cb5ac81..bedfab98077a 100644 --- a/arch/x86/pci/xen.c +++ b/arch/x86/pci/xen.c @@ -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 -- cgit v1.2.3