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SubjectRe: [PATCH 2/3] HYPERV/IOMMU: Add Hyper-V stub IOMMU driver
Hi Sasha:
Thanks for your review.

On Fri, Feb 1, 2019 at 10:51 PM Sasha Levin <sashal@kernel.org> wrote:
>
> Hi Tianyu,
>
> Few comments below.
>
> On Thu, Jan 31, 2019 at 06:17:32PM +0800, lantianyu1986@gmail.com wrote:
> >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.
> >
> >Signed-off-by: Lan Tianyu <Tianyu.Lan@microsoft.com>
> >---
> > drivers/iommu/Kconfig | 7 ++
> > drivers/iommu/Makefile | 1 +
> > drivers/iommu/hyperv-iommu.c | 189 ++++++++++++++++++++++++++++++++++++++++++
> > drivers/iommu/irq_remapping.c | 3 +
> > drivers/iommu/irq_remapping.h | 1 +
> > 5 files changed, 201 insertions(+)
> > create mode 100644 drivers/iommu/hyperv-iommu.c
> >
> >diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> >index 45d7021..5c397c0 100644
> >--- a/drivers/iommu/Kconfig
> >+++ b/drivers/iommu/Kconfig
> >@@ -437,4 +437,11 @@ config QCOM_IOMMU
> > help
> > Support for IOMMU on certain Qualcomm SoCs.
> >
> >+config HYPERV_IOMMU
> >+ bool "Hyper-V stub IOMMU support"
> >+ depends on HYPERV
>
> select IOMMU_API ?

Yes。 will update.

>
> >+ help
> >+ Hyper-V stub IOMMU driver provides capability to run
> >+ Linux guest 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..a64b747
> >--- /dev/null
> >+++ b/drivers/iommu/hyperv-iommu.c
> >@@ -0,0 +1,189 @@
> >+// SPDX-License-Identifier: GPL-2.0
> >+
> >+#define pr_fmt(fmt) "HYPERV-IR: " fmt
> >+
> >+#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"
> >+
> >+/*
> >+ * According IO-APIC spec, IO APIC has a 24-entry Interrupt
> >+ * Redirection Table.
>
> Can the spec be linked somewhere? In the commit message, or here?

Sure. Will update.

>
> >+ */
> >+#define IOAPIC_REMAPPING_ENTRY 24
> >+
> >+static cpumask_t ioapic_max_cpumask = { CPU_BITS_NONE };
> >+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;
> >+ cpumask_t cpumask;
> >+ int ret;
> >+
> >+ cpumask_andnot(&cpumask, mask, &ioapic_max_cpumask);
> >+
> >+ /* Return error If new irq affinity is out of ioapic_max_cpumask. */
> >+ if (!cpumask_empty(&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 IO_APIC_route_entry *entry;
>
> What's the role of this variable? We set it, once, later on in the
> function but that's all?
>

This one should be removed.

> >+ struct irq_data *irq_data;
> >+ struct irq_desc *desc;
> >+ struct irq_cfg *cfg;
> >+ 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)
> >+ goto fail;
> >+
> >+ irq_data = irq_domain_get_irq_data(domain, virq);
> >+ cfg = irqd_cfg(irq_data);
>
> Is this actually being used anywhere, or do we only need it for the
> check below? It's not clear from the code why we're calling irqd_cfg()
> and ignoring the result.

Sorry. irqd_cfg() should not be needed here.

>
> >+ if (!irq_data || !cfg) {
>
> You just dereferenced irq_data in the line above this one, it's a bit
> late to check that it's not NULL.
>

OK. Will update.

> >+ ret = -EINVAL;
> >+ goto fail;
> >+ }
> >+
> >+ irq_data->chip = &hyperv_ir_chip;
> >+
> >+ /*
> >+ * Save IOAPIC entry pointer here in order to set vector and
> >+ * and dest_apicid in the hyperv_irq_remappng_activate()
> >+ * and hyperv_ir_set_affinity(). IOAPIC driver ignores
> >+ * cfg->dest_apicid and cfg->vector when irq remapping
> >+ * mode is enabled. Detail see ioapic_configure_entry().
> >+ */
> >+ irq_data->chip_data = entry = 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_and(desc->irq_common_data.affinity,
> >+ desc->irq_common_data.affinity,
> >+ &ioapic_max_cpumask);
> >+
> >+ fail:
> >+ return ret;
>
> This one doesn't actually free anything?

irq_domain_free_irqs_common() should be called here. Thanks.

>
> >+}
> >+
> >+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_remappng_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_remappng_activate,
> >+};
> >+
> >+static int __init hyperv_prepare_irq_remapping(void)
> >+{
> >+ struct fwnode_handle *fn;
> >+ u32 apic_id;
> >+ int i;
> >+
> >+ if (x86_hyper_type != X86_HYPER_MS_HYPERV ||
> >+ !x2apic_supported())
> >+ return -ENODEV;
> >+
> >+ fn = irq_domain_alloc_named_id_fwnode("HYPERV-IR", 0);
> >+ if (!fn)
> >+ return -EFAULT;
>
> Why EFAULT? The only reason irq_domain_alloc_named_id_fwnode() might
> fail is running out of memory.

ENOMEM should be more accurate.

>
> >+
> >+ 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.
> >+ * 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 255.
>
> Off-by-one here: it'll set the CPU in the affinity mask if it's less
> than 256, not 255.

Yes. will update.

>
> >+ */
> >+ for (i = 0; i < 256; i++) {
> >+ apic_id = cpu_physical_id(i);
> >+ if (apic_id > 255)
> >+ continue;
> >+
> >+ cpumask_set_cpu(i, &ioapic_max_cpumask);
> >+ }
>
> I'm curious here: assuming we have a large amount of CPUs, what
> guarantee do we have that this mask will have anything set? What happens
> if it remains empty?

The APIC id of BSP is always 0. The CPU's APIC ID comes from ACPI MADT table.
The APIC ID in the ACPI MADT table will be monotone increasing from Hyper-V
team.

>
> >+
> >+ 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,
> >+};
> >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
> >



--
Best regards
Tianyu Lan

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