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

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

[Logan Gunthorpe]

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@deltatee.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Christoph Hellwig <hch@lst.de>
---
 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

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

[Bjorn Helgaas]

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@deltatee.com>
> Reviewed-by: Christian König <christian.koenig@amd.com>
> Cc: Bjorn Helgaas <bhelgaas@google.com>
> Cc: Christoph Hellwig <hch@lst.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
>