linux-kernel - Re: [GIT PULL v2] PCI changes for v6.17

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Message-ID: <20250809144927.eUbR3MXg@linutronix.de>
Date: Sat, 9 Aug 2025 16:49:27 +0200
From: Nam Cao <namcao@...utronix.de>
To: Ammar Faizi <ammarfaizi2@...weeb.org>
Cc: Thomas Gleixner <tglx@...utronix.de>, Lukas Wunner <lukas@...ner.de>,
	Bjorn Helgaas <helgaas@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux PCI Mailing List <linux-pci@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Rob Herring <robh@...nel.org>,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	Manivannan Sadhasivam <mani@...nel.org>,
	Krzysztof Wilczynski <kwilczynski@...nel.org>,
	Armando Budianto <sprite@...weeb.org>,
	Alviro Iskandar Setiawan <alviro.iskandar@...weeb.org>,
	gwml@...r.gnuweeb.org, namcaov@...il.com
Subject: Re: [GIT PULL v2] PCI changes for v6.17

On Sat, Aug 09, 2025 at 08:28:39PM +0700, Ammar Faizi wrote:
> On Sat, Aug 09, 2025 at 06:34:29AM +0200, Nam Cao wrote:
> > On Sat, Aug 09, 2025 at 07:52:30AM +0900, Ammar Faizi wrote:
> > > I can do that. Send me a git diff. I'll test it and back with the dmesg
> > > output.
> > 
> > That would be very helpful, thanks!
> > 
> > Please bear with me, this may take a few iterations.
> > 
> > Let's first try the below.
> 
> I just got home from a family outing. A bit slow response.
> 
> Here's the result:
> 
>   https://gist.github.com/ammarfaizi2/ef5f98123ed3868f8d64ed41662edd63#file-dmesg_pci_debug_001-txt-L853

Thanks! Here's the problem:

    [    1.037223] pcieport 10000:e0:1d.0: __pci_enable_msix_range:840 err=hwsize

The PCIe port driver enables interrupt, trying MSI-X first. However, the
device does not support MSI-X, so it tries MSI instead, which triggers
the WARN_ON() in VMD driver.

What's strange is that, the VMD doc says:

    "Intel VMD only supports MSIx Interrupts from child devices and
    therefore the BIOS must enable PCIe Hot Plug and MSIx interrups"

Is it lying to us?

Can you	please try:

    Revert d5c647b08ee0 ("PCI: vmd: Fix wrong kfree() in vmd_msi_free()")
    Revert d7d8ab87e3e7 ("PCI: vmd: Switch to msi_create_parent_irq_domain()")

So that the driver is back to the original state before I touched it.

And apply the diff below. This will tell us if my commit breaks the driver
somehow, or VMD has been allowing MSI all this time.


diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
index d9b893bf4e45..e99d8cefb78d 100644
--- a/drivers/pci/controller/vmd.c
+++ b/drivers/pci/controller/vmd.c
@@ -255,9 +255,15 @@ static int vmd_msi_init(struct irq_domain *domain, struct msi_domain_info *info,
 			msi_alloc_info_t *arg)
 {
 	struct msi_desc *desc = arg->desc;
+	struct pci_dev *pci_dev = msi_desc_to_pci_dev(desc);
 	struct vmd_dev *vmd = vmd_from_bus(msi_desc_to_pci_dev(desc)->bus);
 	struct vmd_irq *vmdirq = kzalloc(sizeof(*vmdirq), GFP_KERNEL);
 
+	if (!pci_msix_vec_count(pci_dev))
+		pr_err("But VMD only supports MSIx Interrupts from child devices!\n");
+	else
+		pr_err("MSI-X, looking good...\n");
+	dump_stack();
 	if (!vmdirq)
 		return -ENOMEM;