linux-kernel - Re: [PATCH] PCI/ACS: Enforce pci=noats with Transaction Blocking

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Message-ID: <20210803232851.GA1585719@bjorn-Precision-5520>
Date:   Tue, 3 Aug 2021 18:28:51 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     linux-pci@...r.kernel.org, bhelgaas@...gle.com, rajatja@...gle.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI/ACS: Enforce pci=noats with Transaction Blocking

On Fri, Jun 18, 2021 at 02:55:14PM -0600, Alex Williamson wrote:
> PCIe Address Translation Services (ATS) provides a mechanism for a
> device to provide an on-device caching translation agent (device
> iotlb).  We already have a means to disable support for this feature
> via the pci=noats option.  For untrusted and externally facing
> devices, we not only disable ATS support for the device, but we use
> Access Control Services (ACS) Transaction Blocking to actively
> prevent devices from sending TLPs with non-default AT field values.
> 
> Extend pci=noats to also make use of PCI_ACS_TB so that not only is
> ATS disabled at the device, but blocked at the downstream ports.
> This provides a means to further lock-down ATS for cases such as
> device assignment, where it may not be the hardware configuration of
> the device that makes it untrusted, but the driver running on the
> device.
> 
> Cc: Rajat Jain <rajatja@...gle.com>
> Signed-off-by: Alex Williamson <alex.williamson@...hat.com>

Applied to pci/virtualization for v5.15, thanks!

> ---
>  drivers/pci/pci.c    |    4 ++--
>  drivers/pci/quirks.c |    2 +-
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 68f57d86b243..5aa1bb2ddd80 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -915,8 +915,8 @@ static void pci_std_enable_acs(struct pci_dev *dev)
>  	/* Upstream Forwarding */
>  	ctrl |= (cap & PCI_ACS_UF);
>  
> -	/* Enable Translation Blocking for external devices */
> -	if (dev->external_facing || dev->untrusted)
> +	/* Enable Translation Blocking for external devices and noats */
> +	if (pci_ats_disabled() || dev->external_facing || dev->untrusted)
>  		ctrl |= (cap & PCI_ACS_TB);
>  
>  	pci_write_config_word(dev, pos + PCI_ACS_CTRL, ctrl);
> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> index 6d74386eadc2..d541076c083a 100644
> --- a/drivers/pci/quirks.c
> +++ b/drivers/pci/quirks.c
> @@ -5031,7 +5031,7 @@ static int pci_quirk_enable_intel_spt_pch_acs(struct pci_dev *dev)
>  	ctrl |= (cap & PCI_ACS_CR);
>  	ctrl |= (cap & PCI_ACS_UF);
>  
> -	if (dev->external_facing || dev->untrusted)
> +	if (pci_ats_disabled() || dev->external_facing || dev->untrusted)
>  		ctrl |= (cap & PCI_ACS_TB);
>  
>  	pci_write_config_dword(dev, pos + INTEL_SPT_ACS_CTRL, ctrl);
> 
>