linux-kernel - Re: [PATCH v3 3/3] PCI/MSI: Convert pci_msi_ignore

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Message-ID: <87v7rxzct0.ffs@tglx>
Date: Tue, 25 Mar 2025 10:20:43 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Roger Pau Monné <roger.pau@...rix.com>, Daniel Gomez
 <da.gomez@...nel.org>
Cc: Jürgen Groß <jgross@...e.com>, Bjorn Helgaas
 <helgaas@...nel.org>,
 linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
 linux-pci@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>, 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>
Subject: Re: [PATCH v3 3/3] PCI/MSI: Convert pci_msi_ignore_mask to per MSI
 domain flag

On Tue, Mar 25 2025 at 09:11, Thomas Gleixner wrote:

> On Mon, Mar 24 2025 at 20:18, Roger Pau Monné wrote:
>> On Mon, Mar 24, 2025 at 07:58:14PM +0100, Daniel Gomez wrote:
>>> The issue is that info appears to be uninitialized. So, this worked for me:
>>
>> Indeed, irq_domain->host_data is NULL, there's no msi_domain_info.  As
>> this is x86, I was expecting x86 ot always use
>> x86_init_dev_msi_info(), but that doesn't seem to be the case.  I
>> would like to better understand this.
>
> Indeed. On x86 this should not happen at all. On architectures, which do
> not use (hierarchical) interrupt domains, it will return NULL.
>
> So I really want to understand why this happens on x86 before such a
> "fix" is deployed.

So after staring at it some more it's clear. Without XEN, the domain
returned is the MSI parent domain, which is the vector domain in that
setup. That does not have a domain info set. But on legacy architectures
there is not even a domain.

It's really wonderful that we have a gazillion ways to manage the
backends of PCI/MSI....

So none of the suggested pointer checks will cover it correctly. Though
there is already a function which allows to query MSI domain flags
independent of the underlying insanity. Sorry for not catching it in
review.

Untested patch below.

Thanks,

        tglx
---
 drivers/pci/msi/msi.c |   18 ++++++------------
 1 file changed, 6 insertions(+), 12 deletions(-)

--- a/drivers/pci/msi/msi.c
+++ b/drivers/pci/msi/msi.c
@@ -285,8 +285,6 @@ static void pci_msi_set_enable(struct pc
 static int msi_setup_msi_desc(struct pci_dev *dev, int nvec,
 			      struct irq_affinity_desc *masks)
 {
-	const struct irq_domain *d = dev_get_msi_domain(&dev->dev);
-	const struct msi_domain_info *info = d->host_data;
 	struct msi_desc desc;
 	u16 control;
 
@@ -297,7 +295,7 @@ static int msi_setup_msi_desc(struct pci
 	/* Lies, damned lies, and MSIs */
 	if (dev->dev_flags & PCI_DEV_FLAGS_HAS_MSI_MASKING)
 		control |= PCI_MSI_FLAGS_MASKBIT;
-	if (info->flags & MSI_FLAG_NO_MASK)
+	if (pci_msi_domain_supports(dev, MSI_FLAG_NO_MASK, DENY_LEGACY))
 		control &= ~PCI_MSI_FLAGS_MASKBIT;
 
 	desc.nvec_used			= nvec;
@@ -605,20 +603,18 @@ static void __iomem *msix_map_region(str
  */
 void msix_prepare_msi_desc(struct pci_dev *dev, struct msi_desc *desc)
 {
-	const struct irq_domain *d = dev_get_msi_domain(&dev->dev);
-	const struct msi_domain_info *info = d->host_data;
-
 	desc->nvec_used				= 1;
 	desc->pci.msi_attrib.is_msix		= 1;
 	desc->pci.msi_attrib.is_64		= 1;
 	desc->pci.msi_attrib.default_irq	= dev->irq;
 	desc->pci.mask_base			= dev->msix_base;
-	desc->pci.msi_attrib.can_mask		= !(info->flags & MSI_FLAG_NO_MASK) &&
-						  !desc->pci.msi_attrib.is_virtual;
 
-	if (desc->pci.msi_attrib.can_mask) {
+
+	if (!pci_msi_domain_supports(dev, MSI_FLAG_NO_MASK, DENY_LEGACY) &&
+	    !desc->pci.msi_attrib.is_virtual) {
 		void __iomem *addr = pci_msix_desc_addr(desc);
 
+		desc->pci.msi_attrib.can_mask = true;
 		desc->pci.msix_ctrl = readl(addr + PCI_MSIX_ENTRY_VECTOR_CTRL);
 	}
 }
@@ -715,8 +711,6 @@ static int msix_setup_interrupts(struct
 static int msix_capability_init(struct pci_dev *dev, struct msix_entry *entries,
 				int nvec, struct irq_affinity *affd)
 {
-	const struct irq_domain *d = dev_get_msi_domain(&dev->dev);
-	const struct msi_domain_info *info = d->host_data;
 	int ret, tsize;
 	u16 control;
 
@@ -747,7 +741,7 @@ static int msix_capability_init(struct p
 	/* Disable INTX */
 	pci_intx_for_msi(dev, 0);
 
-	if (!(info->flags & MSI_FLAG_NO_MASK)) {
+	if (!pci_msi_domain_supports(dev, MSI_FLAG_NO_MASK, DENY_LEGACY)) {
 		/*
 		 * Ensure that all table entries are masked to prevent
 		 * stale entries from firing in a crash kernel.