linux-kernel - Re: [PATCH v2] PCI/P2PDMA: Root complex whitelist should not apply when an IOMMU is present

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Message-ID: <20190619214502.GE143205@google.com>
Date:   Wed, 19 Jun 2019 16:45:02 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     "linux-pci @ vger . kernel . org" <linux-pci@...r.kernel.org>,
        linux-kernel@...r.kernel.org,
        Christian König <christian.koenig@....com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v2] PCI/P2PDMA: Root complex whitelist should not apply
 when an IOMMU is present

On Wed, Jun 19, 2019 at 12:56:26PM -0600, Logan Gunthorpe wrote:
> Presently, there is no path to DMA map P2PDMA memory, so if a TLP
> targeting this memory hits the root complex and an IOMMU is present,
> the IOMMU will reject the transaction, even if the RC would support
> P2PDMA.
> 
> So until the kernel knows to map these DMA addresses in the IOMMU,
> we should not enable the whitelist when an IOMMU is present.
> 
> Link: https://lore.kernel.org/linux-pci/20190522201252.2997-1-logang@deltatee.com/
> Fixes: 0f97da831026 ("PCI/P2PDMA: Allow P2P DMA between any devices under AMD ZEN Root Complex")
> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
> Reviewed-by: Christian König <christian.koenig@....com>
> Cc: Bjorn Helgaas <bhelgaas@...gle.com>
> Cc: Christoph Hellwig <hch@....de>

Applied to for-linus for v5.2, since we merged 0f97da831026 during the v5.2
merge window, thanks!

> ---
>  drivers/pci/p2pdma.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> index a98126ad9c3a..a4994aa3acc0 100644
> --- a/drivers/pci/p2pdma.c
> +++ b/drivers/pci/p2pdma.c
> @@ -18,6 +18,7 @@
>  #include <linux/percpu-refcount.h>
>  #include <linux/random.h>
>  #include <linux/seq_buf.h>
> +#include <linux/iommu.h>
>  
>  struct pci_p2pdma {
>  	struct gen_pool *pool;
> @@ -299,6 +300,9 @@ static bool root_complex_whitelist(struct pci_dev *dev)
>  	struct pci_dev *root = pci_get_slot(host->bus, PCI_DEVFN(0, 0));
>  	unsigned short vendor, device;
>  
> +	if (iommu_present(dev->dev.bus))
> +		return false;
> +
>  	if (!root)
>  		return false;
>  
> -- 
> 2.20.1
>