Re: [PATCH v2] PCI: hv: Fix hibernation in case interrupts are not re-created

[Lorenzo Pieralisi]

[+MarcZ - this patch needs IRQ maintainers vetting]

On Tue, Sep 08, 2020 at 04:17:59PM -0700, Dexuan Cui wrote:
> Hyper-V doesn't trap and emulate the accesses to the MSI/MSI-X registers,
> and we must use hv_compose_msi_msg() to ask Hyper-V to create the IOMMU
> Interrupt Remapping Table Entries. This is not an issue for a lot of
> PCI device drivers (e.g. NVMe driver, Mellanox NIC drivers), which
> destroy and re-create the interrupts across hibernation, so
> hv_compose_msi_msg() is called automatically. However, some other PCI
> device drivers (e.g. the Nvidia driver) may not destroy and re-create
> the interrupts across hibernation, so hv_pci_resume() has to call
> hv_compose_msi_msg(), otherwise the PCI device drivers can no longer
> receive MSI/MSI-X interrupts after hibernation.

This looks like drivers bugs and I don't think the HV controller
driver is where you should fix them. Regardless, this commit log
does not provide the information that it should.

> Fixes: ac82fc832708 ("PCI: hv: Add hibernation support")
> Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
> Reviewed-by: Jake Oshins <jakeo@xxxxxxxxxxxxx>
> 
> ---
> 
> Changes in v2:
>     Fixed a typo in the comment in hv_irq_unmask. Thanks to Michael!
>     Added Jake's Reviewed-by.
> 
>  drivers/pci/controller/pci-hyperv.c | 44 +++++++++++++++++++++++++++++
>  1 file changed, 44 insertions(+)
> 
> diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
> index fc4c3a15e570..dd21afb5d62b 100644
> --- a/drivers/pci/controller/pci-hyperv.c
> +++ b/drivers/pci/controller/pci-hyperv.c
> @@ -1211,6 +1211,21 @@ static void hv_irq_unmask(struct irq_data *data)
>  	pbus = pdev->bus;
>  	hbus = container_of(pbus->sysdata, struct hv_pcibus_device, sysdata);
>  
> +	if (hbus->state == hv_pcibus_removing) {
> +		/*
> +		 * During hibernation, when a CPU is offlined, the kernel tries
> +		 * to move the interrupt to the remaining CPUs that haven't
> +		 * been offlined yet. In this case, the below hv_do_hypercall()
> +		 * always fails since the vmbus channel has been closed, so we
> +		 * should not call the hypercall, but we still need
> +		 * pci_msi_unmask_irq() to reset the mask bit in desc->masked:
> +		 * see cpu_disable_common() -> fixup_irqs() ->
> +		 * irq_migrate_all_off_this_cpu() -> migrate_one_irq().
> +		 */
> +		pci_msi_unmask_irq(data);

This is not appropriate - it looks like a plaster to paper over an
issue with hyper-V hibernation code sequence. Fix that issue instead
of papering over it here.

Thanks,
Lorenzo

> +		return;
> +	}
> +
>  	spin_lock_irqsave(&hbus->retarget_msi_interrupt_lock, flags);
>  
>  	params = &hbus->retarget_msi_interrupt_params;
> @@ -3372,6 +3387,33 @@ static int hv_pci_suspend(struct hv_device *hdev)
>  	return 0;
>  }
>  
> +static int hv_pci_restore_msi_msg(struct pci_dev *pdev, void *arg)
> +{
> +	struct msi_desc *entry;
> +	struct irq_data *irq_data;
> +
> +	for_each_pci_msi_entry(entry, pdev) {
> +		irq_data = irq_get_irq_data(entry->irq);
> +		if (WARN_ON_ONCE(!irq_data))
> +			return -EINVAL;
> +
> +		hv_compose_msi_msg(irq_data, &entry->msg);
> +	}
> +
> +	return 0;
> +}
> +
> +/*
> + * Upon resume, pci_restore_msi_state() -> ... ->  __pci_write_msi_msg()
> + * re-writes the MSI/MSI-X registers, but since Hyper-V doesn't trap and
> + * emulate the accesses, we have to call hv_compose_msi_msg() to ask
> + * Hyper-V to re-create the IOMMU Interrupt Remapping Table Entries.
> + */
> +static void hv_pci_restore_msi_state(struct hv_pcibus_device *hbus)
> +{
> +	pci_walk_bus(hbus->pci_bus, hv_pci_restore_msi_msg, NULL);
> +}
> +
>  static int hv_pci_resume(struct hv_device *hdev)
>  {
>  	struct hv_pcibus_device *hbus = hv_get_drvdata(hdev);
> @@ -3405,6 +3447,8 @@ static int hv_pci_resume(struct hv_device *hdev)
>  
>  	prepopulate_bars(hbus);
>  
> +	hv_pci_restore_msi_state(hbus);
> +
>  	hbus->state = hv_pcibus_installed;
>  	return 0;
>  out:
> -- 
> 2.19.1
>