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Message-ID: <20250821073403.GA29749@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
Date: Thu, 21 Aug 2025 00:34:03 -0700
From: Shradha Gupta <shradhagupta@...ux.microsoft.com>
To: Nam Cao <namcao@...utronix.de>
Cc: "K . Y . Srinivasan" <kys@...rosoft.com>,
Nuno Das Neves <nunodasneves@...ux.microsoft.com>,
Marc Zyngier <maz@...nel.org>,
Haiyang Zhang <haiyangz@...rosoft.com>,
Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
"H . Peter Anvin" <hpa@...or.com>, linux-hyperv@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/1] x86/hyperv: Switch to
msi_create_parent_irq_domain()
On Fri, Jul 18, 2025 at 09:57:50PM +0200, Nam Cao wrote:
> Move away from the legacy MSI domain setup, switch to use
> msi_create_parent_irq_domain().
>
> While doing the conversion, I noticed that hv_irq_compose_msi_msg() is
> doing more than it is supposed to (composing message content). The
> interrupt allocation bits should be moved into hv_msi_domain_alloc().
> However, I have no hardware to test this change, therefore I leave a TODO
> note.
Hi Nam,
JFYI, I am working on a patch to optimize the hv_irq_compose_msi_msg()
callback to prevent potential busy looping due to
PCI_CREATE_INTERRUPT_MESSAGE hypercall. I think I can handle this TODO
in that patch
Thanks,
Shradha
>
> Signed-off-by: Nam Cao <namcao@...utronix.de>
> ---
> arch/x86/hyperv/irqdomain.c | 111 ++++++++++++++++++++++++------------
> drivers/hv/Kconfig | 1 +
> 2 files changed, 77 insertions(+), 35 deletions(-)
>
> diff --git a/arch/x86/hyperv/irqdomain.c b/arch/x86/hyperv/irqdomain.c
> index 090f5ac9f492..c3ba12b1bc07 100644
> --- a/arch/x86/hyperv/irqdomain.c
> +++ b/arch/x86/hyperv/irqdomain.c
> @@ -11,6 +11,7 @@
> #include <linux/pci.h>
> #include <linux/irq.h>
> #include <linux/export.h>
> +#include <linux/irqchip/irq-msi-lib.h>
> #include <asm/mshyperv.h>
>
> static int hv_map_interrupt(union hv_device_id device_id, bool level,
> @@ -289,59 +290,99 @@ static void hv_teardown_msi_irq(struct pci_dev *dev, struct irq_data *irqd)
> (void)hv_unmap_msi_interrupt(dev, &old_entry);
> }
>
> -static void hv_msi_free_irq(struct irq_domain *domain,
> - struct msi_domain_info *info, unsigned int virq)
> -{
> - struct irq_data *irqd = irq_get_irq_data(virq);
> - struct msi_desc *desc;
> -
> - if (!irqd)
> - return;
> -
> - desc = irq_data_get_msi_desc(irqd);
> - if (!desc || !desc->irq || WARN_ON_ONCE(!dev_is_pci(desc->dev)))
> - return;
> -
> - hv_teardown_msi_irq(to_pci_dev(desc->dev), irqd);
> -}
> -
> /*
> * IRQ Chip for MSI PCI/PCI-X/PCI-Express Devices,
> * which implement the MSI or MSI-X Capability Structure.
> */
> static struct irq_chip hv_pci_msi_controller = {
> .name = "HV-PCI-MSI",
> - .irq_unmask = pci_msi_unmask_irq,
> - .irq_mask = pci_msi_mask_irq,
> .irq_ack = irq_chip_ack_parent,
> - .irq_retrigger = irq_chip_retrigger_hierarchy,
> .irq_compose_msi_msg = hv_irq_compose_msi_msg,
> - .irq_set_affinity = msi_domain_set_affinity,
> - .flags = IRQCHIP_SKIP_SET_WAKE | IRQCHIP_MOVE_DEFERRED,
> + .irq_set_affinity = irq_chip_set_affinity_parent,
> };
>
> -static struct msi_domain_ops pci_msi_domain_ops = {
> - .msi_free = hv_msi_free_irq,
> - .msi_prepare = pci_msi_prepare,
> +static bool hv_init_dev_msi_info(struct device *dev, struct irq_domain *domain,
> + struct irq_domain *real_parent, struct msi_domain_info *info)
> +{
> + struct irq_chip *chip = info->chip;
> +
> + if (!msi_lib_init_dev_msi_info(dev, domain, real_parent, info))
> + return false;
> +
> + chip->flags |= IRQCHIP_SKIP_SET_WAKE | IRQCHIP_MOVE_DEFERRED;
> +
> + info->ops->msi_prepare = pci_msi_prepare;
> +
> + return true;
> +}
> +
> +#define HV_MSI_FLAGS_SUPPORTED (MSI_GENERIC_FLAGS_MASK | MSI_FLAG_PCI_MSIX)
> +#define HV_MSI_FLAGS_REQUIRED (MSI_FLAG_USE_DEF_DOM_OPS | MSI_FLAG_USE_DEF_CHIP_OPS)
> +
> +static struct msi_parent_ops hv_msi_parent_ops = {
> + .supported_flags = HV_MSI_FLAGS_SUPPORTED,
> + .required_flags = HV_MSI_FLAGS_REQUIRED,
> + .bus_select_token = DOMAIN_BUS_NEXUS,
> + .bus_select_mask = MATCH_PCI_MSI,
> + .chip_flags = MSI_CHIP_FLAG_SET_ACK,
> + .prefix = "HV-",
> + .init_dev_msi_info = hv_init_dev_msi_info,
> };
>
> -static struct msi_domain_info hv_pci_msi_domain_info = {
> - .flags = MSI_FLAG_USE_DEF_DOM_OPS | MSI_FLAG_USE_DEF_CHIP_OPS |
> - MSI_FLAG_PCI_MSIX,
> - .ops = &pci_msi_domain_ops,
> - .chip = &hv_pci_msi_controller,
> - .handler = handle_edge_irq,
> - .handler_name = "edge",
> +static int hv_msi_domain_alloc(struct irq_domain *d, unsigned int virq, unsigned int nr_irqs,
> + void *arg)
> +{
> + /*
> + * TODO: The allocation bits of hv_irq_compose_msi_msg(), i.e. everything except
> + * entry_to_msi_msg() should be in here.
> + */
> +
> + int ret;
> +
> + ret = irq_domain_alloc_irqs_parent(d, virq, nr_irqs, arg);
> + if (ret)
> + return ret;
> +
> + for (int i = 0; i < nr_irqs; ++i) {
> + irq_domain_set_info(d, virq + i, 0, &hv_pci_msi_controller, NULL,
> + handle_edge_irq, NULL, "edge");
> + }
> + return 0;
> +}
> +
> +static void hv_msi_domain_free(struct irq_domain *d, unsigned int virq, unsigned int nr_irqs)
> +{
> + for (int i = 0; i < nr_irqs; ++i) {
> + struct irq_data *irqd = irq_domain_get_irq_data(d, virq);
> + struct msi_desc *desc;
> +
> + desc = irq_data_get_msi_desc(irqd);
> + if (!desc || !desc->irq || WARN_ON_ONCE(!dev_is_pci(desc->dev)))
> + continue;
> +
> + hv_teardown_msi_irq(to_pci_dev(desc->dev), irqd);
> + }
> + irq_domain_free_irqs_top(d, virq, nr_irqs);
> +}
> +
> +static const struct irq_domain_ops hv_msi_domain_ops = {
> + .select = msi_lib_irq_domain_select,
> + .alloc = hv_msi_domain_alloc,
> + .free = hv_msi_domain_free,
> };
>
> struct irq_domain * __init hv_create_pci_msi_domain(void)
> {
> struct irq_domain *d = NULL;
> - struct fwnode_handle *fn;
>
> - fn = irq_domain_alloc_named_fwnode("HV-PCI-MSI");
> - if (fn)
> - d = pci_msi_create_irq_domain(fn, &hv_pci_msi_domain_info, x86_vector_domain);
> + struct irq_domain_info info = {
> + .fwnode = irq_domain_alloc_named_fwnode("HV-PCI-MSI"),
> + .ops = &hv_msi_domain_ops,
> + .parent = x86_vector_domain,
> + };
> +
> + if (info.fwnode)
> + d = msi_create_parent_irq_domain(&info, &hv_msi_parent_ops);
>
> /* No point in going further if we can't get an irq domain */
> BUG_ON(!d);
> diff --git a/drivers/hv/Kconfig b/drivers/hv/Kconfig
> index 57623ca7f350..9afffedce290 100644
> --- a/drivers/hv/Kconfig
> +++ b/drivers/hv/Kconfig
> @@ -10,6 +10,7 @@ config HYPERV
> select X86_HV_CALLBACK_VECTOR if X86
> select OF_EARLY_FLATTREE if OF
> select SYSFB if EFI && !HYPERV_VTL_MODE
> + select IRQ_MSI_LIB if X86
> help
> Select this option to run Linux as a Hyper-V client operating
> system.
> --
> 2.49.0
>
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