RE: [PATCH] genirq/msi: Activate Multi-MSI early when MSI_FLAG_ACTIVATE_EARLY is set

Shameerali Kolothum Thodi
2021-01-25T16:37:36Z

> -----Original Message-----
> From: Marc Zyngier [mailto:maz@kernel.org]
> Sent: 23 January 2021 12:28
> To: linux-kernel@vger.kernel.org
> Cc: Thomas Gleixner <tglx@linutronix.de>; Bjorn Helgaas
> <bhelgaas@google.com>; Shameerali Kolothum Thodi
> <shameerali.kolothum.thodi@huawei.com>; stable@vger.kernel.org
> Subject: [PATCH] genirq/msi: Activate Multi-MSI early when
> MSI_FLAG_ACTIVATE_EARLY is set
>
> When MSI_FLAG_ACTIVATE_EARLY is set (which is the case for PCI),
> we perform the activation of the interrupt (which in the case of
> PCI results in the endpoint being programmed) as soon as the
> interrupt is allocated.
>
> But it appears that this is only done for the first vector,
> introducing an inconsistent behaviour for PCI Multi-MSI.
>
> Fix it by iterating over the number of vectors allocated to
> each MSI descriptor. This is easily achieved by introducing
> a new "for_each_msi_vector" iterator, together with a tiny
> bit of refactoring.
>
> Fixes: f3b0946d629c ("genirq/msi: Make sure PCI MSIs are activated early")
> Reported-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> Cc: stable@vger.kernel.org
> ---
> include/linux/msi.h | 6 ++++++
> kernel/irq/msi.c | 44 ++++++++++++++++++++------------------------
> 2 files changed, 26 insertions(+), 24 deletions(-)
>
> diff --git a/include/linux/msi.h b/include/linux/msi.h
> index 360a0a7e7341..aef35fd1cf11 100644
> --- a/include/linux/msi.h
> +++ b/include/linux/msi.h
> @@ -178,6 +178,12 @@ struct msi_desc {
> list_for_each_entry((desc), dev_to_msi_list((dev)), list)
> #define for_each_msi_entry_safe(desc, tmp, dev) \
> list_for_each_entry_safe((desc), (tmp), dev_to_msi_list((dev)), list)
> +#define for_each_msi_vector(desc, __irq, dev) \
> + for_each_msi_entry((desc), (dev)) \
> + if ((desc)->irq) \
> + for (__irq = (desc)->irq; \
> + __irq < ((desc)->irq + (desc)->nvec_used); \
> + __irq++)
>
> #ifdef CONFIG_IRQ_MSI_IOMMU
> static inline const void *msi_desc_get_iommu_cookie(struct msi_desc *desc)
> diff --git a/kernel/irq/msi.c b/kernel/irq/msi.c
> index 2c0c4d6d0f83..d924676c8781 100644
> --- a/kernel/irq/msi.c
> +++ b/kernel/irq/msi.c
> @@ -436,22 +436,22 @@ int __msi_domain_alloc_irqs(struct irq_domain
> *domain, struct device *dev,
>
> can_reserve = msi_check_reservation_mode(domain, info, dev);
>
> - for_each_msi_entry(desc, dev) {
> - virq = desc->irq;
> - if (desc->nvec_used == 1)
> - dev_dbg(dev, "irq %d for MSI\n", virq);
> - else
> + /*
> + * This flag is set by the PCI layer as we need to activate
> + * the MSI entries before the PCI layer enables MSI in the
> + * card. Otherwise the card latches a random msi message.
> + */
> + if (!(info->flags & MSI_FLAG_ACTIVATE_EARLY))
> + goto skip_activate;

This will change the dbg print behavior. From the commit f3b0946d629c,
it looks like the below dev_dbg() code was there for !MSI_FLAG_ACTIVATE_EARLY
case as well. Not sure how much this matters though.

Thanks,
Shameer

> +
> + for_each_msi_vector(desc, i, dev) {
> + if (desc->irq == i) {
> + virq = desc->irq;
> dev_dbg(dev, "irq [%d-%d] for MSI\n",
> virq, virq + desc->nvec_used - 1);
> - /*
> - * This flag is set by the PCI layer as we need to activate
> - * the MSI entries before the PCI layer enables MSI in the
> - * card. Otherwise the card latches a random msi message.
> - */
> - if (!(info->flags & MSI_FLAG_ACTIVATE_EARLY))
> - continue;
> + }
>
> - irq_data = irq_domain_get_irq_data(domain, desc->irq);
> + irq_data = irq_domain_get_irq_data(domain, i);
> if (!can_reserve) {
> irqd_clr_can_reserve(irq_data);
> if (domain->flags & IRQ_DOMAIN_MSI_NOMASK_QUIRK)
> @@ -462,28 +462,24 @@ int __msi_domain_alloc_irqs(struct irq_domain
> *domain, struct device *dev,
> goto cleanup;
> }
>
> +skip_activate:
> /*
> * If these interrupts use reservation mode, clear the activated bit
> * so request_irq() will assign the final vector.
> */
> if (can_reserve) {
> - for_each_msi_entry(desc, dev) {
> - irq_data = irq_domain_get_irq_data(domain, desc->irq);
> + for_each_msi_vector(desc, i, dev) {
> + irq_data = irq_domain_get_irq_data(domain, i);
> irqd_clr_activated(irq_data);
> }
> }
> return 0;
>
> cleanup:
> - for_each_msi_entry(desc, dev) {
> - struct irq_data *irqd;
> -
> - if (desc->irq == virq)
> - break;
> -
> - irqd = irq_domain_get_irq_data(domain, desc->irq);
> - if (irqd_is_activated(irqd))
> - irq_domain_deactivate_irq(irqd);
> + for_each_msi_vector(desc, i, dev) {
> + irq_data = irq_domain_get_irq_data(domain, i);
> + if (irqd_is_activated(irq_data))
> + irq_domain_deactivate_irq(irq_data);
> }
> msi_domain_free_irqs(domain, dev);
> return ret;
> --
> 2.29.2