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

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Message-Id: <0B8FAD0D-B598-4CEA-A614-67F4C7C5B9CA@arista.com>
Date:   Tue, 5 Nov 2019 12:17:42 +0000
From:   James Sewart <jamessewart@...sta.com>
To:     iommu@...ts.linux-foundation.org
Cc:     linux-kernel@...r.kernel.org, Dmitry Safonov <dima@...sta.com>
Subject: Re: [PATCH] Ensure pci transactions coming from PLX NTB are handled
 when  IOMMU is turned on

Any comments on this?

Cheers,
James.

> On 24 Oct 2019, at 13:52, James Sewart <jamessewart@...sta.com> wrote:
> 
> 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
> 
>