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

On Thu, Jan 31, 2019 at 10:04 PM Vitaly Kuznetsov <vkuznets@redhat.com> wrote:
>
> lantianyu1986@gmail.com writes:
>
> > 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
> > + 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.
> > + */
> > +#define IOAPIC_REMAPPING_ENTRY 24
>
> KVM already defines KVM_IOAPIC_NUM_PINS - is this the same thing?

It's the same purpose IOMMU driver is out of KVM scope and so define a new one.
Otherwise, this maybe changed in the future when add interrupt
remapping function.

>
> > +
> > +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;
> > + 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);
> > + if (!irq_data || !cfg) {
> > + ret = -EINVAL;
> > + goto fail;
> > + }
>
> fail: label doesn't do anything, you can just return (and you actually
> do on the first failure path).

Yes,will update.

>
> > +
> > + 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 and

Nice catch.

>
> > + * 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().
>
> I would re-phrase this a bit:
>
> /*
> * IOAPIC entry pointer is saved in chip_data to allow
> * hyperv_irq_remappng_activate()/hyperv_ir_set_affinity() to set
> * vector and dest_apicid. cfg->vector and cfg->dest_apicid are
> * ignorred when IRQ remapping is enabled. See ioapic_configure_entry().
> */
>
> But I'm still a bit confused. Hope others are not.

This is better. Thanks.

>
> > + */
> > + irq_data->chip_data = entry = info->ioapic_entry;
> > +
>
> I personally dislike double assignments, hard to remember which one
> happens first :-)

OK. will update.

>
> > + /*
> > + * 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;
> > +}
> > +
> > +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;
> > +
> > + 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.
> > + */
> > + for (i = 0; i < 256; i++) {
> > + apic_id = cpu_physical_id(i);
> > + if (apic_id > 255)
> > + continue;
> > +
> > + cpumask_set_cpu(i, &ioapic_max_cpumask);
> > + }
>
> This is probably not an issue right now, but what if we have > 256 CPUs?
> Assuming there are no CPUs with the same APIC is, would it be better to
> go through all of them seeting bits in ioapic_max_cpumask accordingly?
> (Imagine a situation when CPU257 has APIC id = 1).

The APiC ID assignment with "CPUx"accords the order of local APIC
entry in the ACPI MADT table.
We got that the order will be monotonic increasing from Hyper-V team
.I will add this in the comment
to avoid confusion. APIC IDs reflects cpu topology and so there maybe
some APIC ID gaps(e.g, cpu
number in one socket is a number of power of 2).

>
> > +
> > + 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;
>
> Here we act under assumption that Intel/AMD IOMMUs will never be exposed
> under Hyper-V. It may make sense to actually reverse the order of the
> check: check PV IOMMUs _before_ we actually check for hardware ones.

Yes, this will be better for Hyper-V case but KVM guest and bare metal
use Intel/AMD
IOMMU driver. The function is just called once during boot up and so check order
will not affect boot time too much.

@Joerg Roedel Could you have a look this? Thanks.

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