x86/MSI: Support multiple MSIs in presense of IRQ remapping

The MSI specification has several constraints in comparison with
MSI-X, most notable of them is the inability to configure MSIs
independently. As a result, it is impossible to dispatch
interrupts from different queues to different CPUs. This is
largely devalues the support of multiple MSIs in SMP systems.

Also, a necessity to allocate a contiguous block of vector
numbers for devices capable of multiple MSIs might cause a
considerable pressure on x86 interrupt vector allocator and
could lead to fragmentation of the interrupt vectors space.

This patch overcomes both drawbacks in presense of IRQ remapping
and lets devices take advantage of multiple queues and per-IRQ
affinity assignments.

Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Matthew Wilcox <willy@linux.intel.com>
Cc: Jeff Garzik <jgarzik@pobox.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/c8bd86ff56b5fc118257436768aaa04489ac0a4c.1353324359.git.agordeev@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 133 insertions, 32 deletions

diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
index b739d398bb29..2016f9dabd72 100644
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -300,9 +300,9 @@ static struct irq_cfg *alloc_irq_and_cfg_at(unsigned int at, int node)
         return cfg;
 }
 
-static int alloc_irq_from(unsigned int from, int node)
+static int alloc_irqs_from(unsigned int from, unsigned int count, int node)
 {
-        return irq_alloc_desc_from(from, node);
+        return irq_alloc_descs_from(from, count, node);
 }
 
 static void free_irq_at(unsigned int at, struct irq_cfg *cfg)
@@ -2982,37 +2982,58 @@ device_initcall(ioapic_init_ops);
 /*
  * Dynamic irq allocate and deallocation
  */
-unsigned int create_irq_nr(unsigned int from, int node)
+unsigned int __create_irqs(unsigned int from, unsigned int count, int node)
 {
-        struct irq_cfg *cfg;
+        struct irq_cfg **cfg;
         unsigned long flags;
-        unsigned int ret = 0;
-        int irq;
+        int irq, i;
 
         if (from < nr_irqs_gsi)
                 from = nr_irqs_gsi;
 
-        irq = alloc_irq_from(from, node);
-        if (irq < 0)
-                return 0;
-        cfg = alloc_irq_cfg(irq, node);
-        if (!cfg) {
-                free_irq_at(irq, NULL);
+        cfg = kzalloc_node(count * sizeof(cfg[0]), GFP_KERNEL, node);
+        if (!cfg)
                 return 0;
+
+        irq = alloc_irqs_from(from, count, node);
+        if (irq < 0)
+                goto out_cfgs;
+
+        for (i = 0; i < count; i++) {
+                cfg[i] = alloc_irq_cfg(irq + i, node);
+                if (!cfg[i])
+                        goto out_irqs;
         }
 
         raw_spin_lock_irqsave(&vector_lock, flags);
-        if (!__assign_irq_vector(irq, cfg, apic->target_cpus()))
-                ret = irq;
+        for (i = 0; i < count; i++)
+                if (__assign_irq_vector(irq + i, cfg[i], apic->target_cpus()))
+                        goto out_vecs;
         raw_spin_unlock_irqrestore(&vector_lock, flags);
 
-        if (ret) {
-                irq_set_chip_data(irq, cfg);
-                irq_clear_status_flags(irq, IRQ_NOREQUEST);
-        } else {
-                free_irq_at(irq, cfg);
+        for (i = 0; i < count; i++) {
+                irq_set_chip_data(irq + i, cfg[i]);
+                irq_clear_status_flags(irq + i, IRQ_NOREQUEST);
         }
-        return ret;
+
+        kfree(cfg);
+        return irq;
+
+out_vecs:
+        for (i--; i >= 0; i--)
+                __clear_irq_vector(irq + i, cfg[i]);
+        raw_spin_unlock_irqrestore(&vector_lock, flags);
+out_irqs:
+        for (i = 0; i < count; i++)
+                free_irq_at(irq + i, cfg[i]);
+out_cfgs:
+        kfree(cfg);
+        return 0;
+}
+
+unsigned int create_irq_nr(unsigned int from, int node)
+{
+        return __create_irqs(from, 1, node);
 }
 
 int create_irq(void)
@@ -3045,6 +3066,14 @@ void destroy_irq(unsigned int irq)
         free_irq_at(irq, cfg);
 }
 
+static inline void destroy_irqs(unsigned int irq, unsigned int count)
+{
+        unsigned int i;
+
+        for (i = 0; i < count; i++)
+                destroy_irq(irq + i);
+}
+
 /*
  * MSI message composition
  */
@@ -3071,7 +3100,7 @@ static int msi_compose_msg(struct pci_dev *pdev, unsigned int irq,
 
         if (irq_remapped(cfg)) {
                 compose_remapped_msi_msg(pdev, irq, dest, msg, hpet_id);
-                return err;
+                return 0;
         }
 
         if (x2apic_enabled())
@@ -3098,7 +3127,7 @@ static int msi_compose_msg(struct pci_dev *pdev, unsigned int irq,
                         MSI_DATA_DELIVERY_LOWPRI) |
                 MSI_DATA_VECTOR(cfg->vector);
 
-        return err;
+        return 0;
 }
 
 static int
@@ -3136,18 +3165,26 @@ static struct irq_chip msi_chip = {
         .irq_retrigger          = ioapic_retrigger_irq,
 };
 
-static int setup_msi_irq(struct pci_dev *dev, struct msi_desc *msidesc, int irq)
+static int setup_msi_irq(struct pci_dev *dev, struct msi_desc *msidesc,
+                         unsigned int irq_base, unsigned int irq_offset)
 {
         struct irq_chip *chip = &msi_chip;
         struct msi_msg msg;
+        unsigned int irq = irq_base + irq_offset;
         int ret;
 
         ret = msi_compose_msg(dev, irq, &msg, -1);
         if (ret < 0)
                 return ret;
 
-        irq_set_msi_desc(irq, msidesc);
-        write_msi_msg(irq, &msg);
+        irq_set_msi_desc_off(irq_base, irq_offset, msidesc);
+
+        /*
+         * MSI-X message is written per-IRQ, the offset is always 0.
+         * MSI message denotes a contiguous group of IRQs, written for 0th IRQ.
+         */
+        if (!irq_offset)
+                write_msi_msg(irq, &msg);
 
         if (irq_remapped(irq_get_chip_data(irq))) {
                 irq_set_status_flags(irq, IRQ_MOVE_PCNTXT);
@@ -3161,23 +3198,19 @@ static int setup_msi_irq(struct pci_dev *dev, struct msi_desc *msidesc, int irq)
         return 0;
 }
 
-int native_setup_msi_irqs(struct pci_dev *dev, int nvec, int type)
+int setup_msix_irqs(struct pci_dev *dev, int nvec)
 {
         int node, ret, sub_handle, index = 0;
         unsigned int irq, irq_want;
         struct msi_desc *msidesc;
 
-        /* x86 doesn't support multiple MSI yet */
-        if (type == PCI_CAP_ID_MSI && nvec > 1)
-                return 1;
-
         node = dev_to_node(&dev->dev);
         irq_want = nr_irqs_gsi;
         sub_handle = 0;
         list_for_each_entry(msidesc, &dev->msi_list, list) {
                 irq = create_irq_nr(irq_want, node);
                 if (irq == 0)
-                        return -1;
+                        return -ENOSPC;
                 irq_want = irq + 1;
                 if (!irq_remapping_enabled)
                         goto no_ir;
@@ -3199,7 +3232,7 @@ int native_setup_msi_irqs(struct pci_dev *dev, int nvec, int type)
                                 goto error;
                 }
 no_ir:
-                ret = setup_msi_irq(dev, msidesc, irq);
+                ret = setup_msi_irq(dev, msidesc, irq, 0);
                 if (ret < 0)
                         goto error;
                 sub_handle++;
@@ -3211,6 +3244,74 @@ error:
         return ret;
 }
 
+int setup_msi_irqs(struct pci_dev *dev, int nvec)
+{
+        int node, ret, sub_handle, index = 0;
+        unsigned int irq;
+        struct msi_desc *msidesc;
+
+        if (nvec > 1 && !irq_remapping_enabled)
+                return 1;
+
+        nvec = __roundup_pow_of_two(nvec);
+
+        WARN_ON(!list_is_singular(&dev->msi_list));
+        msidesc = list_entry(dev->msi_list.next, struct msi_desc, list);
+        WARN_ON(msidesc->irq);
+        WARN_ON(msidesc->msi_attrib.multiple);
+
+        node = dev_to_node(&dev->dev);
+        irq = __create_irqs(nr_irqs_gsi, nvec, node);
+        if (irq == 0)
+                return -ENOSPC;
+
+        if (!irq_remapping_enabled) {
+                ret = setup_msi_irq(dev, msidesc, irq, 0);
+                if (ret < 0)
+                        goto error;
+                return 0;
+        }
+
+        msidesc->msi_attrib.multiple = ilog2(nvec);
+        for (sub_handle = 0; sub_handle < nvec; sub_handle++) {
+                if (!sub_handle) {
+                        index = msi_alloc_remapped_irq(dev, irq, nvec);
+                        if (index < 0) {
+                                ret = index;
+                                goto error;
+                        }
+                } else {
+                        ret = msi_setup_remapped_irq(dev, irq + sub_handle,
+                                                     index, sub_handle);
+                        if (ret < 0)
+                                goto error;
+                }
+                ret = setup_msi_irq(dev, msidesc, irq, sub_handle);
+                if (ret < 0)
+                        goto error;
+        }
+        return 0;
+
+error:
+        destroy_irqs(irq, nvec);
+
+        /*
+         * Restore altered MSI descriptor fields and prevent just destroyed
+         * IRQs from tearing down again in default_teardown_msi_irqs()
+         */
+        msidesc->irq = 0;
+        msidesc->msi_attrib.multiple = 0;
+
+        return ret;
+}
+
+int native_setup_msi_irqs(struct pci_dev *dev, int nvec, int type)
+{
+        if (type == PCI_CAP_ID_MSI)
+                return setup_msi_irqs(dev, nvec);
+        return setup_msix_irqs(dev, nvec);
+}
+
 void native_teardown_msi_irq(unsigned int irq)
 {
         destroy_irq(irq);