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Subject[PATCH V4 2/3] HYPERV/IOMMU: Add Hyper-V stub IOMMU driver
Date
From: Lan Tianyu <Tianyu.Lan@microsoft.com>

On the bare metal, enabling X2APIC mode requires interrupt remapping
function which helps to deliver irq to cpu with 32-bit APIC ID.
Hyper-V doesn't provide interrupt remapping function so far and Hyper-V
MSI protocol already supports to deliver interrupt to the CPU whose
virtual processor index is more than 255. IO-APIC interrupt still has
8-bit APIC ID limitation.

This patch is to add Hyper-V stub IOMMU driver in order to enable
X2APIC mode successfully in Hyper-V Linux guest. The driver returns X2APIC
interrupt remapping capability when X2APIC mode is available. Otherwise,
it creates a Hyper-V irq domain to limit IO-APIC interrupts' affinity
and make sure cpus assigned with IO-APIC interrupt have 8-bit APIC ID.

Define 24 IO-APIC remapping entries because Hyper-V only expose one
single IO-APIC and one IO-APIC has 24 pins according IO-APIC spec(
https://pdos.csail.mit.edu/6.828/2016/readings/ia32/ioapic.pdf).

Signed-off-by: Lan Tianyu <Tianyu.Lan@microsoft.com>
---
Change since v3:
- Make Hyper-V IOMMU as Hyper-V default driver
- Fix hypervisor_is_type() input parameter
- Check possible cpu numbers during scan 0~255 cpu's apic id.

Change since v2:
- Improve comment about why save IO-APIC entry in the irq chip data.
- Some code improvement.
- Improve statement in the IOMMU Kconfig.

Change since v1:
- Remove unused pr_fmt
- Make ioapic_ir_domain as static variable
- Remove unused variables cfg and entry in the hyperv_irq_remapping_alloc()
- Fix comments
---
drivers/iommu/Kconfig | 9 ++
drivers/iommu/Makefile | 1 +
drivers/iommu/hyperv-iommu.c | 194 ++++++++++++++++++++++++++++++++++++++++++
drivers/iommu/irq_remapping.c | 3 +
drivers/iommu/irq_remapping.h | 1 +
5 files changed, 208 insertions(+)
create mode 100644 drivers/iommu/hyperv-iommu.c

diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
index 45d7021..6f07f3b 100644
--- a/drivers/iommu/Kconfig
+++ b/drivers/iommu/Kconfig
@@ -437,4 +437,13 @@ config QCOM_IOMMU
help
Support for IOMMU on certain Qualcomm SoCs.

+config HYPERV_IOMMU
+ bool "Hyper-V x2APIC IRQ Handling"
+ depends on HYPERV
+ select IOMMU_API
+ default HYPERV
+ help
+ Stub IOMMU driver to handle IRQs as to allow Hyper-V Linux
+ guests to run with x2APIC mode enabled.
+
endif # IOMMU_SUPPORT
diff --git a/drivers/iommu/Makefile b/drivers/iommu/Makefile
index a158a68..8c71a15 100644
--- a/drivers/iommu/Makefile
+++ b/drivers/iommu/Makefile
@@ -32,3 +32,4 @@ obj-$(CONFIG_EXYNOS_IOMMU) += exynos-iommu.o
obj-$(CONFIG_FSL_PAMU) += fsl_pamu.o fsl_pamu_domain.o
obj-$(CONFIG_S390_IOMMU) += s390-iommu.o
obj-$(CONFIG_QCOM_IOMMU) += qcom_iommu.o
+obj-$(CONFIG_HYPERV_IOMMU) += hyperv-iommu.o
diff --git a/drivers/iommu/hyperv-iommu.c b/drivers/iommu/hyperv-iommu.c
new file mode 100644
index 0000000..c61240e0
--- /dev/null
+++ b/drivers/iommu/hyperv-iommu.c
@@ -0,0 +1,194 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Hyper-V stub IOMMU driver.
+ *
+ * Copyright (C) 2019, Microsoft, Inc.
+ *
+ * Author : Lan Tianyu <Tianyu.Lan@microsoft.com>
+ */
+
+#include <linux/types.h>
+#include <linux/interrupt.h>
+#include <linux/irq.h>
+#include <linux/iommu.h>
+#include <linux/module.h>
+
+#include <asm/hw_irq.h>
+#include <asm/io_apic.h>
+#include <asm/irq_remapping.h>
+#include <asm/hypervisor.h>
+
+#include "irq_remapping.h"
+
+#ifdef CONFIG_IRQ_REMAP
+
+/*
+ * According 82093AA IO-APIC spec , IO APIC has a 24-entry Interrupt
+ * Redirection Table. Hyper-V exposes one single IO-APIC and so define
+ * 24 IO APIC remmapping entries.
+ */
+#define IOAPIC_REMAPPING_ENTRY 24
+
+static cpumask_t ioapic_max_cpumask = { CPU_BITS_NONE };
+static struct irq_domain *ioapic_ir_domain;
+
+static int hyperv_ir_set_affinity(struct irq_data *data,
+ const struct cpumask *mask, bool force)
+{
+ struct irq_data *parent = data->parent_data;
+ struct irq_cfg *cfg = irqd_cfg(data);
+ struct IO_APIC_route_entry *entry;
+ int ret;
+
+ /* Return error If new irq affinity is out of ioapic_max_cpumask. */
+ if (!cpumask_subset(mask, &ioapic_max_cpumask))
+ return -EINVAL;
+
+ ret = parent->chip->irq_set_affinity(parent, mask, force);
+ if (ret < 0 || ret == IRQ_SET_MASK_OK_DONE)
+ return ret;
+
+ entry = data->chip_data;
+ entry->dest = cfg->dest_apicid;
+ entry->vector = cfg->vector;
+ send_cleanup_vector(cfg);
+
+ return 0;
+}
+
+static struct irq_chip hyperv_ir_chip = {
+ .name = "HYPERV-IR",
+ .irq_ack = apic_ack_irq,
+ .irq_set_affinity = hyperv_ir_set_affinity,
+};
+
+static int hyperv_irq_remapping_alloc(struct irq_domain *domain,
+ unsigned int virq, unsigned int nr_irqs,
+ void *arg)
+{
+ struct irq_alloc_info *info = arg;
+ struct irq_data *irq_data;
+ struct irq_desc *desc;
+ int ret = 0;
+
+ if (!info || info->type != X86_IRQ_ALLOC_TYPE_IOAPIC || nr_irqs > 1)
+ return -EINVAL;
+
+ ret = irq_domain_alloc_irqs_parent(domain, virq, nr_irqs, arg);
+ if (ret < 0)
+ return ret;
+
+ irq_data = irq_domain_get_irq_data(domain, virq);
+ if (!irq_data) {
+ irq_domain_free_irqs_common(domain, virq, nr_irqs);
+ return -EINVAL;
+ }
+
+ irq_data->chip = &hyperv_ir_chip;
+
+ /*
+ * If there is interrupt remapping function of IOMMU, setting irq
+ * affinity only needs to change IRTE of IOMMU. But Hyper-V doesn't
+ * support interrupt remapping function, setting irq affinity of IO-APIC
+ * interrupts still needs to change IO-APIC registers. But ioapic_
+ * configure_entry() will ignore value of cfg->vector and cfg->
+ * dest_apicid when IO-APIC's parent irq domain is not the vector
+ * domain.(See ioapic_configure_entry()) In order to setting vector
+ * and dest_apicid to IO-APIC register, IO-APIC entry pointer is saved
+ * in the chip_data and hyperv_irq_remapping_activate()/hyperv_ir_set_
+ * affinity() set vector and dest_apicid directly into IO-APIC entry.
+ */
+ irq_data->chip_data = info->ioapic_entry;
+
+ /*
+ * Hypver-V IO APIC irq affinity should be in the scope of
+ * ioapic_max_cpumask because no irq remapping support.
+ */
+ desc = irq_data_to_desc(irq_data);
+ cpumask_copy(desc->irq_common_data.affinity, &ioapic_max_cpumask);
+
+ return 0;
+}
+
+static void hyperv_irq_remapping_free(struct irq_domain *domain,
+ unsigned int virq, unsigned int nr_irqs)
+{
+ irq_domain_free_irqs_common(domain, virq, nr_irqs);
+}
+
+static int hyperv_irq_remapping_activate(struct irq_domain *domain,
+ struct irq_data *irq_data, bool reserve)
+{
+ struct irq_cfg *cfg = irqd_cfg(irq_data);
+ struct IO_APIC_route_entry *entry = irq_data->chip_data;
+
+ entry->dest = cfg->dest_apicid;
+ entry->vector = cfg->vector;
+
+ return 0;
+}
+
+static struct irq_domain_ops hyperv_ir_domain_ops = {
+ .alloc = hyperv_irq_remapping_alloc,
+ .free = hyperv_irq_remapping_free,
+ .activate = hyperv_irq_remapping_activate,
+};
+
+static int __init hyperv_prepare_irq_remapping(void)
+{
+ struct fwnode_handle *fn;
+ int i;
+
+ if (!hypervisor_is_type(X86_HYPER_MS_HYPERV) ||
+ !x2apic_supported())
+ return -ENODEV;
+
+ fn = irq_domain_alloc_named_id_fwnode("HYPERV-IR", 0);
+ if (!fn)
+ return -ENOMEM;
+
+ ioapic_ir_domain =
+ irq_domain_create_hierarchy(arch_get_ir_parent_domain(),
+ 0, IOAPIC_REMAPPING_ENTRY, fn,
+ &hyperv_ir_domain_ops, NULL);
+
+ irq_domain_free_fwnode(fn);
+
+ /*
+ * Hyper-V doesn't provide irq remapping function for
+ * IO-APIC and so IO-APIC only accepts 8-bit APIC ID.
+ * Cpu's APIC ID is read from ACPI MADT table and APIC IDs
+ * in the MADT table on Hyper-v are sorted monotonic increasingly.
+ * APIC ID reflects cpu topology. There maybe some APIC ID
+ * gaps when cpu number in a socket is not power of two. Prepare
+ * max cpu affinity for IOAPIC irqs. Scan cpu 0-255 and set cpu
+ * into ioapic_max_cpumask if its APIC ID is less than 256.
+ */
+ for (i = min_t(unsigned int, num_possible_cpus(), 255); i >= 0; i--)
+ if (cpu_physical_id(i) < 256)
+ cpumask_set_cpu(i, &ioapic_max_cpumask);
+
+ return 0;
+}
+
+static int __init hyperv_enable_irq_remapping(void)
+{
+ return IRQ_REMAP_X2APIC_MODE;
+}
+
+static struct irq_domain *hyperv_get_ir_irq_domain(struct irq_alloc_info *info)
+{
+ if (info->type == X86_IRQ_ALLOC_TYPE_IOAPIC)
+ return ioapic_ir_domain;
+ else
+ return NULL;
+}
+
+struct irq_remap_ops hyperv_irq_remap_ops = {
+ .prepare = hyperv_prepare_irq_remapping,
+ .enable = hyperv_enable_irq_remapping,
+ .get_ir_irq_domain = hyperv_get_ir_irq_domain,
+};
+
+#endif
diff --git a/drivers/iommu/irq_remapping.c b/drivers/iommu/irq_remapping.c
index b94ebd4..81cf290 100644
--- a/drivers/iommu/irq_remapping.c
+++ b/drivers/iommu/irq_remapping.c
@@ -103,6 +103,9 @@ int __init irq_remapping_prepare(void)
else if (IS_ENABLED(CONFIG_AMD_IOMMU) &&
amd_iommu_irq_ops.prepare() == 0)
remap_ops = &amd_iommu_irq_ops;
+ else if (IS_ENABLED(CONFIG_HYPERV_IOMMU) &&
+ hyperv_irq_remap_ops.prepare() == 0)
+ remap_ops = &hyperv_irq_remap_ops;
else
return -ENOSYS;

diff --git a/drivers/iommu/irq_remapping.h b/drivers/iommu/irq_remapping.h
index 0afef6e..f8609e9 100644
--- a/drivers/iommu/irq_remapping.h
+++ b/drivers/iommu/irq_remapping.h
@@ -64,6 +64,7 @@ struct irq_remap_ops {

extern struct irq_remap_ops intel_irq_remap_ops;
extern struct irq_remap_ops amd_iommu_irq_ops;
+extern struct irq_remap_ops hyperv_irq_remap_ops;

#else /* CONFIG_IRQ_REMAP */

--
2.7.4
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