Re: [PATCH] irqdomain: Add the missing assignment of domain->fwnode for named fwnode

[Marc Zyngier]

Hi Dexuan,

On 03/09/2019 00:14, Dexuan Cui wrote:
> 
> Recently device pass-through stops working for Linux VM running on Hyper-V.
> 
> git-bisect shows the regression is caused by the recent commit
> 467a3bb97432 ("PCI: hv: Allocate a named fwnode ..."), but the root cause
> is that the commit d59f6617eef0 forgets to set the domain->fwnode for
> IRQCHIP_FWNODE_NAMED*, and as a result:
> 
> 1. The domain->fwnode remains to be NULL.
> 
> 2. irq_find_matching_fwspec() returns NULL since "h->fwnode == fwnode" is
> false, and pci_set_bus_msi_domain() sets the Hyper-V PCI root bus's
> msi_domain to NULL.
> 
> 3. When the device is added onto the root bus, the device's dev->msi_domain
> is set to NULL in pci_set_msi_domain().
> 
> 4. When a device driver tries to enable MSI-X, pci_msi_setup_msi_irqs()
> calls arch_setup_msi_irqs(), which uses the native MSI chip (i.e.
> arch/x86/kernel/apic/msi.c: pci_msi_controller) to set up the irqs, but
> actually pci_msi_setup_msi_irqs() is supposed to call
> msi_domain_alloc_irqs() with the hbus->irq_domain, which is created in
> hv_pcie_init_irq_domain() and is associated with the Hyper-V chip
> hv_msi_irq_chip. Consequently, the irq line is not properly set up, and
> the device driver can not receive any interrupt.
> 
> Fixes: d59f6617eef0 ("genirq: Allow fwnode to carry name information only")
> Fixes: 467a3bb97432 ("PCI: hv: Allocate a named fwnode instead of an address-based one")
> Reported-by: Lili Deng <v-lide@xxxxxxxxxxxxx>
> Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
> ---
> 
> Note: the commit 467a3bb97432 ("PCI: hv: Allocate a named fwnode ...") has not
> gone in Linus's tree yet (the commit is in linux-next for a while), so the commit ID
> in the changelog can change when it goes in Linus's tree.

This branch is supposed to be stable, and I try to only apply fixes to
it. This normally ensures that commit IDs are the same once they land in
Linus' tree.

> This patch works in my test, but I'm not 100% sure this is the right fix. 
> 
> Looking forward to your comment!
> 
>  kernel/irq/irqdomain.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/irq/irqdomain.c b/kernel/irq/irqdomain.c
> index e7bbab149750..132672b74e4b 100644
> --- a/kernel/irq/irqdomain.c
> +++ b/kernel/irq/irqdomain.c
> @@ -149,6 +149,7 @@ struct irq_domain *__irq_domain_add(struct fwnode_handle *fwnode, int size,
>  		switch (fwid->type) {
>  		case IRQCHIP_FWNODE_NAMED:
>  		case IRQCHIP_FWNODE_NAMED_ID:
> +			domain->fwnode = fwnode;
>  			domain->name = kstrdup(fwid->name, GFP_KERNEL);
>  			if (!domain->name) {
>  				kfree(domain);
> 

Looks absolutely correct to me, thanks for fixing it. I've applied it on
top of irqchip-next.

Thanks,

	M.
-- 
Jazz is not dead, it just smells funny...