From 2cffad7bad83157f89332872015f4305d2ac09ac Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Wed, 13 Sep 2017 23:29:53 +0200
Subject: x86/irq: Simplify hotplug vector accounting

Before a CPU is taken offline the number of active interrupt vectors on the
outgoing CPU and the number of vectors which are available on the other
online CPUs are counted and compared. If the active vectors are more than
the available vectors on the other CPUs then the CPU hot-unplug operation
is aborted. This again uses loop based search and is inaccurate.

The bitmap matrix allocator has accurate accounting information and can
tell exactly whether the vector space is sufficient or not.

Emit a message when the number of globaly reserved (unallocated) vectors is
larger than the number of available vectors after offlining a CPU because
after that point request_irq() might fail.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Juergen Gross <jgross@suse.com>
Tested-by: Yu Chen <yu.c.chen@intel.com>
Acked-by: Juergen Gross <jgross@suse.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Alok Kataria <akataria@vmware.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Rui Zhang <rui.zhang@intel.com>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Len Brown <lenb@kernel.org>
Link: https://lkml.kernel.org/r/20170913213156.351193962@linutronix.de
---
 arch/x86/kernel/apic/vector.c | 32 +++++++++++++++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)

(limited to 'arch/x86/kernel/apic/vector.c')

diff --git a/arch/x86/kernel/apic/vector.c b/arch/x86/kernel/apic/vector.c
index 5e58da8efe77..14b21ca4483c 100644
--- a/arch/x86/kernel/apic/vector.c
+++ b/arch/x86/kernel/apic/vector.c
@@ -945,7 +945,37 @@ void irq_force_complete_move(struct irq_desc *desc)
 unlock:
 	raw_spin_unlock(&vector_lock);
 }
-#endif
+
+#ifdef CONFIG_HOTPLUG_CPU
+/*
+ * Note, this is not accurate accounting, but at least good enough to
+ * prevent that the actual interrupt move will run out of vectors.
+ */
+int lapic_can_unplug_cpu(void)
+{
+	unsigned int rsvd, avl, tomove, cpu = smp_processor_id();
+	int ret = 0;
+
+	raw_spin_lock(&vector_lock);
+	tomove = irq_matrix_allocated(vector_matrix);
+	avl = irq_matrix_available(vector_matrix, true);
+	if (avl < tomove) {
+		pr_warn("CPU %u has %u vectors, %u available. Cannot disable CPU\n",
+			cpu, tomove, avl);
+		ret = -ENOSPC;
+		goto out;
+	}
+	rsvd = irq_matrix_reserved(vector_matrix);
+	if (avl < rsvd) {
+		pr_warn("Reserved vectors %u > available %u. IRQ request may fail\n",
+			rsvd, avl);
+	}
+out:
+	raw_spin_unlock(&vector_lock);
+	return ret;
+}
+#endif /* HOTPLUG_CPU */
+#endif /* SMP */
 
 static void __init print_APIC_field(int base)
 {
-- 
cgit