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Date: Fri, 12 Aug 2016 13:43:35 +0200
From: Paolo Bonzini <pbonzini@...hat.com>
To: alex.popov@...ux.com
Cc: Thomas Gleixner <tglx@...utronix.de>,
Christoph Hellwig <hch@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Marc Zyngier <marc.zyngier@....com>,
"H. Peter Anvin" <hpa@...or.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Kees Cook <keescook@...omium.org>,
Dmitry Vyukov <dvyukov@...gle.com>,
Jiang Liu <jiang.liu@...ux.intel.com>,
Jason Cooper <jason@...edaemon.net>,
Radim Krcmar <rkrcmar@...hat.com>,
Joerg Roedel <joro@...tes.org>, linux-kernel@...r.kernel.org,
x86@...nel.org, kvm@...r.kernel.org
Subject: Re: [PATCH 1/1] x86/apic: Introduce paravirq irq_domain
On 12/08/2016 12:56, Alexander Popov wrote:
> Maybe the name "paravirq" is not very good, I'll try to describe the idea.
>
> There is some kernel module for special interactions between guest VMs.
> Currently it has to register a MSI-capable PCI device to handle interrupts
> injected by the hypervisor. And the bare-metal hypervisor has to emulate
> such a device for guest VMs.
>
> So I've implemented paravirq irq_domain to avoid this redundant emulation.
> With it we can just call:
> - paravirq_alloc_irq() to allocate a LAPIC irq;
> - request_irq() for it;
> - irqd_cfg(irq_get_irq_data()) to get the corresponding interrupt vector
> and inform the hypervisor about it.
> Now we happily handle the irq from the hypervisor when it injects this vector.
>
> The irq_mask/irq_unmask parameters of paravirq_init_chip() are the pointers
> to the functions from the interaction module which ask the hypervisor to
> start/stop injecting interrupts to the guest VM.
>
> Paravirq irq_domain allows to avoid the PCI device emulation in the hypervisor
> and provides the ability to run slimmer Linux guests without precompiled
> PCI and MSI support.
>
> Did I manage to answer your questions?
It's a bit clearer. My doubt is that the caller of paravirq_init_chip
has to provide irq_mask and irq_unmask, but it doesn't know who will
call paravirq_alloc_irq. So there are two cases:
1) there is only one device, and then your solution doesn't scale well
to multiple devices
2) there is some kind of commonality between all devices using
paravirq_alloc_irq, and then it should be abstracted in a bus.
The latter would be similar to what Xen and Hyper-V do, for example.
Using PCI is more similar to the KVM approach.
Paolo
> Please correct me if the idea is wrong or there's a better way to do that.
> Thanks.
>
>>> Signed-off-by: Alexander Popov <alex.popov@...ux.com>
>>> ---
>>> arch/x86/Kconfig | 8 +++
>>> arch/x86/include/asm/irqdomain.h | 6 ++
>>> arch/x86/include/asm/paravirq.h | 9 +++
>>> arch/x86/kernel/apic/Makefile | 2 +
>>> arch/x86/kernel/apic/paravirq.c | 128
>>> +++++++++++++++++++++++++++++++++++++++
>>> arch/x86/kernel/apic/vector.c | 1 +
>>> 6 files changed, 154 insertions(+)
>>> create mode 100644 arch/x86/include/asm/paravirq.h
>>> create mode 100644 arch/x86/kernel/apic/paravirq.c
>>>
>>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>>> index 5c6e747..209bd88 100644
>>> --- a/arch/x86/Kconfig
>>> +++ b/arch/x86/Kconfig
>>> @@ -760,6 +760,14 @@ config PARAVIRT_TIME_ACCOUNTING
>>>
>>> If in doubt, say N here.
>>>
>>> +config X86_PARAVIRQ
>>> + bool "Enable paravirq irq_domain"
>>> + depends on PARAVIRT && X86_LOCAL_APIC
>>> + default n
>>> + ---help---
>>> + This option enables paravirq irq_domain for interrupts injected
>>> + by the hypervisor using Intel VT-x technology.
>>> +
>>> config PARAVIRT_CLOCK
>>> bool
>>>
>>> diff --git a/arch/x86/include/asm/irqdomain.h
>>> b/arch/x86/include/asm/irqdomain.h
>>> index d26075b..e3192f6 100644
>>> --- a/arch/x86/include/asm/irqdomain.h
>>> +++ b/arch/x86/include/asm/irqdomain.h
>>> @@ -60,4 +60,10 @@ extern void arch_init_htirq_domain(struct irq_domain
>>> *domain);
>>> static inline void arch_init_htirq_domain(struct irq_domain *domain) { }
>>> #endif
>>>
>>> +#ifdef CONFIG_X86_PARAVIRQ
>>> +extern void arch_init_paravirq_domain(struct irq_domain *domain);
>>> +#else
>>> +static inline void arch_init_paravirq_domain(struct irq_domain *domain) { }
>>> +#endif
>>> +
>>> #endif
>>> diff --git a/arch/x86/include/asm/paravirq.h
>>> b/arch/x86/include/asm/paravirq.h
>>> new file mode 100644
>>> index 0000000..a137de2
>>> --- /dev/null
>>> +++ b/arch/x86/include/asm/paravirq.h
>>> @@ -0,0 +1,9 @@
>>> +#ifndef _ASM_X86_PARAVIRQ_H
>>> +#define _ASM_X86_PARAVIRQ_H
>>> +
>>> +int paravirq_init_chip(void (*irq_mask)(struct irq_data *data),
>>> + void (*irq_unmask)(struct irq_data *data));
>>> +int paravirq_alloc_irq(void);
>>> +void paravirq_free_irq(unsigned int irq);
>>> +
>>> +#endif /* _ASM_X86_PARAVIRQ_H */
>>> diff --git a/arch/x86/kernel/apic/Makefile b/arch/x86/kernel/apic/Makefile
>>> index 8e63ebd..84f9ce0 100644
>>> --- a/arch/x86/kernel/apic/Makefile
>>> +++ b/arch/x86/kernel/apic/Makefile
>>> @@ -28,3 +28,5 @@ obj-$(CONFIG_X86_BIGSMP) += bigsmp_32.o
>>>
>>> # For 32bit, probe_32 need to be listed last
>>> obj-$(CONFIG_X86_LOCAL_APIC) += probe_$(BITS).o
>>> +
>>> +obj-$(CONFIG_X86_PARAVIRQ) += paravirq.o
>>> diff --git a/arch/x86/kernel/apic/paravirq.c
>>> b/arch/x86/kernel/apic/paravirq.c
>>> new file mode 100644
>>> index 0000000..430b819
>>> --- /dev/null
>>> +++ b/arch/x86/kernel/apic/paravirq.c
>>> @@ -0,0 +1,128 @@
>>> +/*
>>> + * An irq_domain for interrupts injected by the hypervisor using
>>> + * Intel VT-x technology.
>>> + *
>>> + * Copyright (C) 2016 Alexander Popov <alex.popov@...ux.com>.
>>> + *
>>> + * This file is released under the GPLv2.
>>> + */
>>> +
>>> +#include <linux/init.h>
>>> +#include <linux/irq.h>
>>> +#include <asm/irqdomain.h>
>>> +#include <asm/paravirq.h>
>>> +
>>> +static struct irq_domain *paravirq_domain;
>>> +
>>> +static struct irq_chip paravirq_chip = {
>>> + .name = "PARAVIRQ",
>>> + .irq_ack = irq_chip_ack_parent,
>>> +};
>>> +
>>> +static int paravirq_domain_alloc(struct irq_domain *domain,
>>> + unsigned int virq, unsigned int nr_irqs, void *arg)
>>> +{
>>> + int ret = 0;
>>> +
>>> + BUG_ON(domain != paravirq_domain);
>>> +
>>> + if (nr_irqs != 1)
>>> + return -EINVAL;
>>> +
>>> + ret = irq_domain_set_hwirq_and_chip(paravirq_domain,
>>> + virq, virq, ¶virq_chip, NULL);
>>> + if (ret) {
>>> + pr_warn("setting chip, hwirq for irq %u failed\n", virq);
>>> + return ret;
>>> + }
>>> +
>>> + __irq_set_handler(virq, handle_edge_irq, 0, "edge");
>>> +
>>> + return 0;
>>> +}
>>> +
>>> +static void paravirq_domain_free(struct irq_domain *domain,
>>> + unsigned int virq, unsigned int nr_irqs)
>>> +{
>>> + struct irq_data *irq_data;
>>> +
>>> + BUG_ON(domain != paravirq_domain);
>>> + BUG_ON(nr_irqs != 1);
>>> +
>>> + irq_data = irq_domain_get_irq_data(paravirq_domain, virq);
>>> + if (irq_data)
>>> + irq_domain_reset_irq_data(irq_data);
>>> + else
>>> + pr_warn("irq %u is not in paravirq irq_domain\n", virq);
>>> +}
>>> +
>>> +static const struct irq_domain_ops paravirq_domain_ops = {
>>> + .alloc = paravirq_domain_alloc,
>>> + .free = paravirq_domain_free,
>>> +};
>>> +
>>> +int paravirq_alloc_irq(void)
>>> +{
>>> + struct irq_alloc_info info;
>>> +
>>> + if (!paravirq_domain)
>>> + return -ENODEV;
>>> +
>>> + if (!paravirq_chip.irq_mask || !paravirq_chip.irq_unmask)
>>> + return -EINVAL;
>>> +
>>> + init_irq_alloc_info(&info, NULL);
>>> +
>>> + return irq_domain_alloc_irqs(paravirq_domain, 1, NUMA_NO_NODE, &info);
>>> +}
>>> +EXPORT_SYMBOL(paravirq_alloc_irq);
>>> +
>>> +void paravirq_free_irq(unsigned int virq)
>>> +{
>>> + struct irq_data *irq_data;
>>> +
>>> + if (!paravirq_domain) {
>>> + pr_warn("paravirq irq_domain is not initialized\n");
>>> + return;
>>> + }
>>> +
>>> + irq_data = irq_domain_get_irq_data(paravirq_domain, virq);
>>> + if (irq_data)
>>> + irq_domain_free_irqs(virq, 1);
>>> + else
>>> + pr_warn("irq %u is not in paravirq irq_domain\n", virq);
>>> +}
>>> +EXPORT_SYMBOL(paravirq_free_irq);
>>> +
>>> +int paravirq_init_chip(void (*irq_mask)(struct irq_data *data),
>>> + void (*irq_unmask)(struct irq_data *data))
>>> +{
>>> + if (!paravirq_domain)
>>> + return -ENODEV;
>>> +
>>> + if (paravirq_chip.irq_mask || paravirq_chip.irq_unmask)
>>> + return -EEXIST;
>>> +
>>> + if (!irq_mask || !irq_unmask)
>>> + return -EINVAL;
>>> +
>>> + paravirq_chip.irq_mask = irq_mask;
>>> + paravirq_chip.irq_unmask = irq_unmask;
>>> +
>>> + return 0;
>>> +}
>>> +EXPORT_SYMBOL(paravirq_init_chip);
>>> +
>>> +void arch_init_paravirq_domain(struct irq_domain *parent)
>>> +{
>>> + paravirq_domain = irq_domain_add_tree(NULL, ¶virq_domain_ops, NULL);
>>> + if (!paravirq_domain) {
>>> + pr_warn("failed to initialize paravirq irq_domain\n");
>>> + return;
>>> + }
>>> +
>>> + paravirq_domain->name = paravirq_chip.name;
>>> + paravirq_domain->parent = parent;
>>> + paravirq_domain->flags |= IRQ_DOMAIN_FLAG_AUTO_RECURSIVE;
>>> +}
>>> +
>>> diff --git a/arch/x86/kernel/apic/vector.c b/arch/x86/kernel/apic/vector.c
>>> index 6066d94..878b440 100644
>>> --- a/arch/x86/kernel/apic/vector.c
>>> +++ b/arch/x86/kernel/apic/vector.c
>>> @@ -438,6 +438,7 @@ int __init arch_early_irq_init(void)
>>>
>>> arch_init_msi_domain(x86_vector_domain);
>>> arch_init_htirq_domain(x86_vector_domain);
>>> + arch_init_paravirq_domain(x86_vector_domain);
>>>
>>> BUG_ON(!alloc_cpumask_var(&vector_cpumask, GFP_KERNEL));
>>> BUG_ON(!alloc_cpumask_var(&vector_searchmask, GFP_KERNEL));
>>> --
>>> 2.5.5
>>>
>>>
>
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