Date:   Thu, 7 Oct 2021 23:41:12 +0000
From:   Sunil Muthuswamy <sunilmut@...rosoft.com>
To:     Marc Zyngier <maz@...nel.org>
CC:     Michael Kelley <mikelley@...rosoft.com>,
        Boqun Feng <Boqun.Feng@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Dexuan Cui <decui@...rosoft.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        "Krzysztof Wilczyński" <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Wei Liu <wei.liu@...nel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [EXTERNAL] Re: [PATCH 2/2] PCI: hv: Support for Hyper-V vPCI for
 ARM64

On Mon, September 13, 2021 12:03 PM
Marc Zyngier <maz@...nel.org> wrote:

> > --- /dev/null
> > +++ b/arch/arm64/hyperv/hv_pci.c
> 
> Nit: this is definitely the wrong location. There isn't anything arm64
> specific here that warrants hiding it away. Like most other bizarre
> MSI implementation, it should either live in drivers/pci or in
> drivers/irqchip.
>
Thanks. I am moving all of this to drivers/pci/controller in v2.

> > @@ -0,0 +1,275 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +/*
> > + * Architecture specific vector management for the Hyper-V vPCI.
> > + *
> > + * Copyright (C) 2018, Microsoft, Inc.
> > + *
> > + * Author : Sunil Muthuswamy <sunilmut@...rosoft.com>
> > + *
> > + * This program is free software; you can redistribute it and/or modify it
> > + * under the terms of the GNU General Public License version 2 as
> published
> > + * by the Free Software Foundation.
> > + *
> > + * This program is distributed in the hope that it will be useful, but
> > + * WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD
> TITLE or
> > + * NON INFRINGEMENT. See the GNU General Public License for more
> > + * details.
> 
> What is the point of this if you have the SPDX tag?
> 
Will be fixed in V2

> > +/*
> > + * SPI vectors to use for vPCI; arch SPIs range is [32, 1019], but leaving a bit
> > + * of room at the start to allow for SPIs to be specified through ACPI.
> > + */
> > +#define HV_PCI_MSI_SPI_START	50
> 
> If that's the start, it has a good chance of being the wrong
> start. Given that the HyperV PCI controller advertises Multi-MSI
> support, INTID 50 cannot be used for any device that requires more
> than 2 vectors.
> 
Moved to a power of 2, in v2. More comments below.

> > +#define HV_PCI_MSI_SPI_NR	(1020 - HV_PCI_MSI_SPI_START)
> > +
> > +struct hv_pci_chip_data {
> > +	spinlock_t lock;
> 
> Why a spinlock? Either this can be used in interrupt context, and we
> require a raw_spinlock_t instead, or it never is used in interrupt
> context and should be a good old mutex.
> 
Good call. Upon reviewing the requirements again, I believe we can get
away with just a mutex.

> > +	DECLARE_BITMAP(bm, HV_PCI_MSI_SPI_NR);
> > +};
> > +
> > +/* Hyper-V vPCI MSI GIC IRQ domain */
> > +static struct irq_domain *hv_msi_gic_irq_domain;
> > +
> > +static struct irq_chip hv_msi_irq_chip = {
> > +	.name = "Hyper-V ARM64 PCI MSI",
> 
> That's a mouthful! How about "MSI" instead?
> 
Will be addressed in V2.

> > +	.irq_set_affinity = irq_chip_set_affinity_parent,
> > +	.irq_eoi = irq_chip_eoi_parent,
> > +	.irq_mask = irq_chip_mask_parent,
> > +	.irq_unmask = irq_chip_unmask_parent
> > +};
> > +
> > +/**
> > + * Frees the specified number of interrupts.
> > + * @domain: The IRQ domain
> > + * @virq: The virtual IRQ number.
> > + * @nr_irqs: Number of IRQ's to free.
> > + */
> > +static void hv_pci_vec_irq_domain_free(struct irq_domain *domain,
> > +				       unsigned int virq, unsigned int nr_irqs)
> > +{
> > +	struct hv_pci_chip_data *chip_data = domain->host_data;
> > +	unsigned long flags;
> > +	unsigned int i;
> > +
> > +	for (i = 0; i < nr_irqs; i++) {
> > +		struct irq_data *irqd = irq_domain_get_irq_data(domain,
> > +								virq + i);
> > +
> > +		spin_lock_irqsave(&chip_data->lock, flags);
> > +		clear_bit(irqd->hwirq - HV_PCI_MSI_SPI_START, chip_data-
> >bm);
> > +		spin_unlock_irqrestore(&chip_data->lock, flags);
> 
> Really? Why should you disable interrupts here? Why do you need to
> lock/unlock on each iteration of this loop?
> 
Good call. In v2, I am moving to using bitmap region to satisfy Multi-MSI
requirements and that should also take care of this.

> > +		irq_domain_reset_irq_data(irqd);
> > +	}
> > +
> > +	irq_domain_free_irqs_parent(domain, virq, nr_irqs);
> > +}
> > +
> > +/**
> > + * Allocate an interrupt from the domain.
> > + * @hwirq: Will be set to the allocated H/W IRQ.
> > + *
> > + * Return: 0 on success and error value on failure.
> > + */
> > +static int hv_pci_vec_alloc_device_irq(struct irq_domain *domain,
> > +				unsigned int virq, irq_hw_number_t *hwirq)
> > +{
> > +	struct hv_pci_chip_data *chip_data = domain->host_data;
> > +	unsigned long flags;
> > +	unsigned int index;
> > +
> > +	spin_lock_irqsave(&chip_data->lock, flags);
> > +	index = find_first_zero_bit(chip_data->bm, HV_PCI_MSI_SPI_NR);
> > +	if (index == HV_PCI_MSI_SPI_NR) {
> > +		spin_unlock_irqrestore(&chip_data->lock, flags);
> > +		pr_err("No more free IRQ vector available\n");
> 
> No, we don't shout because we're out of MSIs. It happens, and drivers
> can nicely use less vectors if needed.
> 
> But more importantly, this is totally breaks MultiMSI, see below.
> 
'pr_err' removed in v2 and more comments below on Mult-MSI.

> > +		return -ENOSPC;
> > +	}
> > +
> > +	set_bit(index, chip_data->bm);
> > +	spin_unlock_irqrestore(&chip_data->lock, flags);
> > +	*hwirq = index + HV_PCI_MSI_SPI_START;
> > +
> > +	return 0;
> > +}
> > +
> > +/**
> > + * Allocate an interrupt from the parent GIC domain.
> > + * @domain: The IRQ domain.
> > + * @virq: The virtual IRQ number.
> > + * @hwirq: The H/W IRQ number that needs to be allocated.
> > + *
> > + * Return: 0 on success and error value on failure.
> > + */
> > +static int hv_pci_vec_irq_gic_domain_alloc(struct irq_domain *domain,
> > +					   unsigned int virq,
> > +					   irq_hw_number_t hwirq)
> > +{
> > +	struct irq_fwspec fwspec;
> > +
> > +	fwspec.fwnode = domain->parent->fwnode;
> > +	fwspec.param_count = 2;
> > +	fwspec.param[0] = hwirq;
> > +	fwspec.param[1] = IRQ_TYPE_EDGE_RISING;
> > +
> > +	return irq_domain_alloc_irqs_parent(domain, virq, 1, &fwspec);
> > +}
> > +
> > +/**
> > + * Allocate specified number of interrupts from the domain.
> > + * @domain: The IRQ domain.
> > + * @virq: The starting virtual IRQ number.
> > + * @nr_irqs: Number of IRQ's to allocate.
> > + * @args: The MSI alloc information.
> > + *
> > + * Return: 0 on success and error value on failure.
> > + */
> > +static int hv_pci_vec_irq_domain_alloc(struct irq_domain *domain,
> > +				       unsigned int virq, unsigned int nr_irqs,
> > +				       void *args)
> > +{
> > +	irq_hw_number_t hwirq;
> > +	unsigned int i;
> > +	int ret;
> > +
> > +	for (i = 0; i < nr_irqs; i++) {
> > +		ret = hv_pci_vec_alloc_device_irq(domain, virq, &hwirq);
> > +		if (ret)
> > +			goto free_irq;
> > +
> > +		ret = hv_pci_vec_irq_gic_domain_alloc(domain, virq + i,
> hwirq);
> 
> Please read the specification for PCI MultiMSI. You offer none of the
> alignment and contiguity guarantees that are required.
> 
Good call on Multi-MSI and thank you! I am looking to address this in
v2. But, the 'MSI_FLAG_MULTI_PCI_MSI' flag that we set today in 
Hyper-V vPCI, even for x64 seems wrong and broken. We only allocate
one vector at a time from the Hypervisor. That's not going to work with
Multi-MSI. See 'vector_count' in 'hv_compose_msi_req_v2'.
Nevertheless, I do agree with you that if we are implementing something
new, we should be able to at least keep that clean. The Hyper-V vPCI
bug can be addressed separately.

> > +		if (ret)
> > +			goto free_irq;
> > +
> > +		ret = irq_domain_set_hwirq_and_chip(domain, virq + i,
> > +				hwirq, &hv_msi_irq_chip,
> > +				domain->host_data);
> > +		if (ret)
> > +			goto free_irq;
> > +
> > +
> 	irqd_set_single_target(irq_desc_get_irq_data(irq_to_desc(virq +
> i)));
> 
> Why? The GIC is responsible for the distribution, not the MSI layer.
> This looks completely bogus.
> 
Thanks. Will be removed in v2.

> > +		pr_debug("pID:%d vID:%u\n", (int)hwirq, virq + i);
> > +	}
> > +
> > +	return 0;
> > +
> > +free_irq:
> > +	if (i > 0)
> > +		hv_pci_vec_irq_domain_free(domain, virq, i - 1);
> > +
> > +	return ret;
> > +}
> > +
> > +/**
> > + * Activate the interrupt.
> > + * @domain: The IRQ domain.
> > + * @irqd: IRQ data.
> > + * @reserve: Indicates whether the IRQ's can be reserved.
> > + *
> > + * Return: 0 on success and error value on failure.
> > + */
> > +static int hv_pci_vec_irq_domain_activate(struct irq_domain *domain,
> > +					  struct irq_data *irqd, bool reserve)
> > +{
> > +	/* All available online CPUs are available for targeting */
> > +	irq_data_update_effective_affinity(irqd, cpu_online_mask);
> 
> Which completely contradicts what you have written above, and doesn't
> match what the GIC does either.
> 
We will need to still support this as when Hyper-V vPCI composes the MSI
message (' hv_compose_msi_req_get_cpu'), it will pick the first available CPU
from online cpu mask.

> > +	return 0;
> > +}
> > +
> > +static const struct irq_domain_ops hv_pci_domain_ops = {
> > +	.alloc	= hv_pci_vec_irq_domain_alloc,
> > +	.free	= hv_pci_vec_irq_domain_free,
> > +	.activate = hv_pci_vec_irq_domain_activate,
> > +};
> > +
> > +
> > +/**
> > + * This routine performs the architecture specific initialization for vector
> > + * domain to operate. It allocates an IRQ domain tree as a child of the GIC
> > + * IRQ domain.
> > + *
> > + * Return: 0 on success and error value on failure.
> > + */
> > +int hv_pci_vector_init(void)
> 
> Why isn't this static?
> 
Thanks. This is getting rearranged in v2.

> > +{
> > +	static struct hv_pci_chip_data *chip_data;
> > +	struct fwnode_handle *fn = NULL;
> > +	int ret = -ENOMEM;
> > +
> > +	chip_data = kzalloc(sizeof(*chip_data), GFP_KERNEL);
> > +	if (!chip_data)
> > +		return ret;
> > +
> > +	spin_lock_init(&chip_data->lock);
> > +	fn = irq_domain_alloc_named_fwnode("Hyper-V ARM64 vPCI");
> > +	if (!fn)
> > +		goto free_chip;
> > +
> > +	hv_msi_gic_irq_domain = acpi_irq_create_hierarchy(0,
> HV_PCI_MSI_SPI_NR,
> > +					fn, &hv_pci_domain_ops, chip_data);
> > +
> > +	if (!hv_msi_gic_irq_domain) {
> > +		pr_err("Failed to create Hyper-V ARMV vPCI MSI IRQ
> domain\n");
> > +		goto free_chip;
> > +	}
> > +
> > +	return 0;
> > +
> > +free_chip:
> > +	kfree(chip_data);
> > +	if (fn)
> > +		irq_domain_free_fwnode(fn);
> > +
> > +	return ret;
> > +}
> > +
> > +/* This routine performs the cleanup for the IRQ domain. */
> > +void hv_pci_vector_free(void)
> 
> Why isn't this static?
> 
Thanks. This is getting rearranged in v2.

> > +{
> > +	static struct hv_pci_chip_data *chip_data;
> > +
> > +	if (!hv_msi_gic_irq_domain)
> > +		return;
> > +
> > +	/* Host data cannot be null if the domain was created successfully */
> > +	chip_data = hv_msi_gic_irq_domain->host_data;
> > +	irq_domain_remove(hv_msi_gic_irq_domain);
> > +	hv_msi_gic_irq_domain = NULL;
> > +	kfree(chip_data);
> > +}
> > +
> > +/* Performs the architecture specific initialization for Hyper-V vPCI. */
> > +int hv_pci_arch_init(void)
> > +{
> > +	return hv_pci_vector_init();
> > +}
> > +EXPORT_SYMBOL_GPL(hv_pci_arch_init);
> > +
> > +/* Architecture specific cleanup for Hyper-V vPCI. */
> > +void hv_pci_arch_free(void)
> > +{
> > +	hv_pci_vector_free();
> > +}
> > +EXPORT_SYMBOL_GPL(hv_pci_arch_free);
> > +
> > +struct irq_domain *hv_msi_parent_vector_domain(void)
> > +{
> > +	return hv_msi_gic_irq_domain;
> > +}
> > +EXPORT_SYMBOL_GPL(hv_msi_parent_vector_domain);
> > +
> > +unsigned int hv_msi_get_int_vector(struct irq_data *irqd)
> > +{
> > +	irqd = irq_domain_get_irq_data(hv_msi_gic_irq_domain, irqd->irq);
> > +
> > +	return irqd->hwirq;
> > +}
> > +EXPORT_SYMBOL_GPL(hv_msi_get_int_vector);
> 
> I fail to understand why this is all exported instead of being part of
> the HyperV PCI module.
> 
Thanks. Yes, this will all become part of the Hyper-V vPCI module in v2
with the code rearrangement.

> > diff --git a/arch/arm64/include/asm/hyperv-tlfs.h
> b/arch/arm64/include/asm/hyperv-tlfs.h
> > index 4d964a7f02ee..bc6c7ac934a1 100644
> > --- a/arch/arm64/include/asm/hyperv-tlfs.h
> > +++ b/arch/arm64/include/asm/hyperv-tlfs.h
> > @@ -64,6 +64,15 @@
> >  #define HV_REGISTER_STIMER0_CONFIG	0x000B0000
> >  #define HV_REGISTER_STIMER0_COUNT	0x000B0001
> >
> > +union hv_msi_entry {
> > +	u64 as_uint64[2];
> > +	struct {
> > +		u64 address;
> > +		u32 data;
> > +		u32 reserved;
> > +	} __packed;
> > +};
> > +
> >  #include <asm-generic/hyperv-tlfs.h>
> >
> >  #endif
> > diff --git a/arch/arm64/include/asm/mshyperv.h
> b/arch/arm64/include/asm/mshyperv.h
> > index 20070a847304..68bc1617707b 100644
> > --- a/arch/arm64/include/asm/mshyperv.h
> > +++ b/arch/arm64/include/asm/mshyperv.h
> > @@ -20,6 +20,8 @@
> >
> >  #include <linux/types.h>
> >  #include <linux/arm-smccc.h>
> > +#include <linux/interrupt.h>
> > +#include <linux/msi.h>
> >  #include <asm/hyperv-tlfs.h>
> >
> >  /*
> > @@ -49,6 +51,30 @@ static inline u64 hv_get_register(unsigned int reg)
> >  				ARM_SMCCC_OWNER_VENDOR_HYP,	\
> >  				HV_SMCCC_FUNC_NUMBER)
> >
> > +#define hv_msi_handler			NULL
> > +#define hv_msi_handler_name		NULL
> > +#define hv_msi_irq_delivery_mode	0
> > +#define hv_msi_prepare NULL
> > +
> > +int hv_pci_arch_init(void);
> > +void hv_pci_arch_free(void);
> > +struct irq_domain *hv_msi_parent_vector_domain(void);
> > +unsigned int hv_msi_get_int_vector(struct irq_data *data);
> > +static inline irq_hw_number_t
> > +hv_msi_domain_ops_get_hwirq(struct msi_domain_info *info,
> > +			    msi_alloc_info_t *arg)
> > +{
> > +	return arg->hwirq;
> > +}
> > +
> > +static inline void hv_set_msi_entry_from_desc(union hv_msi_entry
> *msi_entry,
> > +					      struct msi_desc *msi_desc)
> > +{
> > +	msi_entry->address = ((u64)msi_desc->msg.address_hi << 32) |
> > +			      msi_desc->msg.address_lo;
> > +	msi_entry->data = msi_desc->msg.data;
> > +}
> 
> Why do we need any of this? Why inline? Please explain what you are
> trying to achieve here.
> 
This is because the 'hv_msi_entry' structure is defined differently by
the Hyper-V for x64 and arm64 (x64 doesn't has the high part of address).
And, so this is just to handle that difference.

Appreciate all of your inputs. v2 is coming up.

- Sunil

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