linux-kernel - [PATCH] Ensure pci transactions coming from PLX NTB are handled when IOMMU is turned on

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Message-Id: <A3FA9DE1-2EEF-41D8-9AC2-B1F760E7F5D5@arista.com>
Date:   Thu, 24 Oct 2019 13:52:19 +0100
From:   James Sewart <jamessewart@...sta.com>
To:     iommu@...ts.linux-foundation.org
Cc:     linux-kernel@...r.kernel.org, Dmitry Safonov <dima@...sta.com>
Subject: [PATCH] Ensure pci transactions coming from PLX NTB are handled when 
 IOMMU is turned on

The PLX PEX NTB forwards DMA transactions using Requester ID's that don't exist as
PCI devices. The devfn for a transaction is used as an index into a lookup table
storing the origin of a transaction on the other side of the bridge.

This patch aliases all possible devfn's to the NTB device so that any transaction
coming in is governed by the mappings for the NTB.

Signed-Off-By: James Sewart <jamessewart@...sta.com>
---
 drivers/pci/quirks.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
index 320255e5e8f8..647f546e427f 100644
--- a/drivers/pci/quirks.c
+++ b/drivers/pci/quirks.c
@@ -5315,6 +5315,28 @@ SWITCHTEC_QUIRK(0x8574);  /* PFXI 64XG3 */
 SWITCHTEC_QUIRK(0x8575);  /* PFXI 80XG3 */
 SWITCHTEC_QUIRK(0x8576);  /* PFXI 96XG3 */
 
+/*
+ * PLX NTB uses devfn proxy IDs to move TLPs between NT endpoints. These IDs
+ * are used to forward responses to the originator on the other side of the
+ * NTB. Alias all possible IDs to the NTB to permit access when the IOMMU is
+ * turned on.
+ */
+static void quirk_PLX_NTB_dma_alias(struct pci_dev *pdev)
+{
+	if (!pdev->dma_alias_mask)
+		pdev->dma_alias_mask = kcalloc(BITS_TO_LONGS(U8_MAX),
+					      sizeof(long), GFP_KERNEL);
+	if (!pdev->dma_alias_mask) {
+		dev_warn(&pdev->dev, "Unable to allocate DMA alias mask\n");
+		return;
+	}
+
+	// PLX NTB may use all 256 devfns
+	memset(pdev->dma_alias_mask, U8_MAX, (U8_MAX+1)/BITS_PER_BYTE);
+}
+DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_PLX, 0x87b0, quirk_PLX_NTB_dma_alias);
+DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_PLX, 0x87b1, quirk_PLX_NTB_dma_alias);
+
 /*
  * On Lenovo Thinkpad P50 SKUs with a Nvidia Quadro M1000M, the BIOS does
  * not always reset the secondary Nvidia GPU between reboots if the system
-- 
2.19.1