Re: [core-for-CI PATCH] thunderbolt: Add Kconfig option to disable PCIe tunneling

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Tue, Jun 04, 2024 at 07:16:18PM +0300, Imre Deak wrote:
> From: Mika Westerberg <mika.westerberg@linux.intel.com>
> 
> In typical cases PCIe tunneling is needed to make the devices fully
> usable for the host system. However, it poses a security issue because
> they can also use DMA to access the host memory. We already have two
> ways of preventing this, one an IOMMU that is enabled on recent systems
> by default and the second is the "authorized" attribute under each
> connected device that needs to be written by userspace before a PCIe
> tunnel is created. This option adds one more by adding a Kconfig option,
> which is enabled by default, that can be used to make kernel binaries
> where PCIe tunneling is completely disabled.
> 
> Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> References: https://intel-gfx-ci.01.org/tree/drm-tip/Trybot_134314v1/bat-mtlp-9/boot0.txt
> References: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/11261
> Signed-off-by: Imre Deak <imre.deak@intel.com>
> ---
> 
> The issue at the first References: link is a known false-positive lockdep issue
> in the TBT/PCIe subsystem. After discussion with the TBT maintainer (Mika
> Westerberg), the easiest solution for the iGFX CI is to disable the PCIe TBT
> tunneling functionality which leads to the issue, as
> 
> - It's not an important feature iGFX CI needs to test.
> - There is no available solution (patch) yet to solve the lockdep issue.
> 
> The feature could be re-enabled if needed once the lockdep issue is
> solved upstream. This patch will be merged upstream, until that sending it
> for core-for-CI.

Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

> 
>  drivers/thunderbolt/Kconfig  | 18 ++++++++++++++++++
>  drivers/thunderbolt/tb.c     |  2 +-
>  drivers/thunderbolt/tb.h     |  9 +++++++++
>  drivers/thunderbolt/tunnel.c |  8 ++++----
>  drivers/thunderbolt/usb4.c   |  2 +-
>  5 files changed, 33 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/thunderbolt/Kconfig b/drivers/thunderbolt/Kconfig
> index 448fd2ec8f6e2..facf2e684c022 100644
> --- a/drivers/thunderbolt/Kconfig
> +++ b/drivers/thunderbolt/Kconfig
> @@ -18,6 +18,24 @@ menuconfig USB4
>  
>  if USB4
>  
> +config USB4_PCIE_TUNNELING
> +	bool "Allow PCI Express tunneling over USB4 fabric"
> +	depends on PCI
> +	default y
> +	help
> +	  USB4 and Thunderbolt devices typically include PCIe switch
> +	  with a number of PCIe endpoints such as USB host controllers,
> +	  GPUs and network adapters. These are made available to the
> +	  host system through PCIe tunneling. These can use DMA and
> +	  therefore have access to the host memory which is typically
> +	  guarded by an IOMMU. This option allows disabling PCIe
> +	  tunneling completely.
> +
> +	  For devices to be usable it is recommended to say Y here.
> +
> +	  Note this only works with systems that use Software Based
> +	  Connection Manager (this is most USB4 hosts).
> +
>  config USB4_DEBUGFS_WRITE
>  	bool "Enable write by debugfs to configuration spaces (DANGEROUS)"
>  	help
> diff --git a/drivers/thunderbolt/tb.c b/drivers/thunderbolt/tb.c
> index 10e719dd837ce..7d71ff3f82c13 100644
> --- a/drivers/thunderbolt/tb.c
> +++ b/drivers/thunderbolt/tb.c
> @@ -3181,7 +3181,7 @@ struct tb *tb_probe(struct tb_nhi *nhi)
>  	if (!tb)
>  		return NULL;
>  
> -	if (tb_acpi_may_tunnel_pcie())
> +	if (tb_may_tunnel_pcie())
>  		tb->security_level = TB_SECURITY_USER;
>  	else
>  		tb->security_level = TB_SECURITY_NOPCIE;
> diff --git a/drivers/thunderbolt/tb.h b/drivers/thunderbolt/tb.h
> index 18aae4ccaed59..22fad8a9679ae 100644
> --- a/drivers/thunderbolt/tb.h
> +++ b/drivers/thunderbolt/tb.h
> @@ -1436,6 +1436,15 @@ static inline int tb_acpi_power_on_retimers(struct tb_port *port) { return 0; }
>  static inline int tb_acpi_power_off_retimers(struct tb_port *port) { return 0; }
>  #endif
>  
> +static inline bool tb_may_tunnel_pcie(void)
> +{
> +#ifdef CONFIG_USB4_PCIE_TUNNELING
> +	return tb_acpi_may_tunnel_pcie();
> +#else
> +	return false;
> +#endif
> +}
> +
>  #ifdef CONFIG_DEBUG_FS
>  void tb_debugfs_init(void);
>  void tb_debugfs_exit(void);
> diff --git a/drivers/thunderbolt/tunnel.c b/drivers/thunderbolt/tunnel.c
> index 41cf6378ad251..7c8397c135ba9 100644
> --- a/drivers/thunderbolt/tunnel.c
> +++ b/drivers/thunderbolt/tunnel.c
> @@ -101,7 +101,7 @@ static unsigned int tb_available_credits(const struct tb_port *port,
>  	size_t ndp;
>  
>  	usb3 = tb_acpi_may_tunnel_usb3() ? sw->max_usb3_credits : 0;
> -	pcie = tb_acpi_may_tunnel_pcie() ? sw->max_pcie_credits : 0;
> +	pcie = tb_may_tunnel_pcie() ? sw->max_pcie_credits : 0;
>  
>  	if (tb_acpi_is_xdomain_allowed()) {
>  		spare = min_not_zero(sw->max_dma_credits, dma_credits);
> @@ -426,7 +426,7 @@ bool tb_tunnel_reserved_pci(struct tb_port *port, int *reserved_up,
>  	if (WARN_ON_ONCE(!port->remote))
>  		return false;
>  
> -	if (!tb_acpi_may_tunnel_pcie())
> +	if (!tb_may_tunnel_pcie())
>  		return false;
>  
>  	if (tb_port_get_link_generation(port) < 4)
> @@ -1510,7 +1510,7 @@ static unsigned int tb_dma_available_credits(const struct tb_port *port)
>  	int credits;
>  
>  	credits = tb_available_credits(port, NULL);
> -	if (tb_acpi_may_tunnel_pcie())
> +	if (tb_may_tunnel_pcie())
>  		credits -= sw->max_pcie_credits;
>  	credits -= port->dma_credits;
>  
> @@ -1821,7 +1821,7 @@ static int tb_usb3_consumed_bandwidth(struct tb_tunnel *tunnel,
>  		int *consumed_up, int *consumed_down)
>  {
>  	struct tb_port *port = tb_upstream_port(tunnel->dst_port->sw);
> -	int pcie_weight = tb_acpi_may_tunnel_pcie() ? TB_PCI_WEIGHT : 0;
> +	int pcie_weight = tb_may_tunnel_pcie() ? TB_PCI_WEIGHT : 0;
>  
>  	/*
>  	 * PCIe tunneling, if enabled, affects the USB3 bandwidth so
> diff --git a/drivers/thunderbolt/usb4.c b/drivers/thunderbolt/usb4.c
> index de480bf2a53de..cacc7bec19eb4 100644
> --- a/drivers/thunderbolt/usb4.c
> +++ b/drivers/thunderbolt/usb4.c
> @@ -282,7 +282,7 @@ int usb4_switch_setup(struct tb_switch *sw)
>  	 * Only enable PCIe tunneling if the parent router supports it
>  	 * and it is not disabled.
>  	 */
> -	if (tb_acpi_may_tunnel_pcie() &&
> +	if (tb_may_tunnel_pcie() &&
>  	    tb_switch_find_port(parent, TB_TYPE_PCIE_DOWN)) {
>  		val |= ROUTER_CS_5_PTO;
>  		/*
> -- 
> 2.43.3
>