linux-kernel - [PATCH 2/3] vmd: disable MSI remapping bypass under Xen

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Message-ID: <20250110140152.27624-3-roger.pau@citrix.com>
Date: Fri, 10 Jan 2025 15:01:49 +0100
From: Roger Pau Monne <roger.pau@...rix.com>
To: linux-kernel@...r.kernel.org,
	xen-devel@...ts.xenproject.org,
	linux-pci@...r.kernel.org
Cc: Roger Pau Monne <roger.pau@...rix.com>,
	Nirmal Patel <nirmal.patel@...ux.intel.com>,
	Jonathan Derrick <jonathan.derrick@...ux.dev>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Rob Herring <robh@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>
Subject: [PATCH 2/3] vmd: disable MSI remapping bypass under Xen

MSI remapping bypass (directly configuring MSI entries for devices on the VMD
bus) won't work under Xen, as Xen is not aware of devices in such bus, and
hence cannot configure the entries using the pIRQ interface in the PV case, and
in the PVH case traps won't be setup for MSI entries for such devices.

Until Xen is aware of devices in the VMD bus prevent the
VMD_FEAT_CAN_BYPASS_MSI_REMAP capability from being used when running as any
kind of Xen guest.

Signed-off-by: Roger Pau Monné <roger.pau@...rix.com>
---
 drivers/pci/controller/vmd.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
index 264a180403a0..d9b7510ace29 100644
--- a/drivers/pci/controller/vmd.c
+++ b/drivers/pci/controller/vmd.c
@@ -965,6 +965,15 @@ static int vmd_probe(struct pci_dev *dev, const struct pci_device_id *id)
 	struct vmd_dev *vmd;
 	int err;
 
+	if (xen_domain())
+		/*
+		 * Xen doesn't have knowledge about devices in the VMD bus.
+		 * Bypass of MSI remapping won't work in that case as direct
+		 * write to the MSI entries won't result in functional
+		 * interrupts.
+		 */
+		features &= ~VMD_FEAT_CAN_BYPASS_MSI_REMAP;
+
 	if (resource_size(&dev->resource[VMD_CFGBAR]) < (1 << 20))
 		return -ENOMEM;
 
-- 
2.46.0