linux-kernel - Re: [PATCH] PCI: qcom: Enable BDF to SID translation properly

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Date: Thu, 7 Mar 2024 12:19:56 +0100
From: Konrad Dybcio <konrad.dybcio@...aro.org>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
 Bjorn Andersson <andersson@...nel.org>,
 Lorenzo Pieralisi <lpieralisi@...nel.org>,
 Krzysztof Wilczyński <kw@...ux.com>,
 Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>
Cc: linux-pci@...r.kernel.org, linux-arm-msm@...r.kernel.org,
 linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] PCI: qcom: Enable BDF to SID translation properly



On 3/7/24 12:05, Manivannan Sadhasivam wrote:
> Qcom SoCs making use of ARM SMMU require BDF to SID translation table in
> the driver to properly map the SID for the PCIe devices based on their BDF
> identifier. This is currently achieved with the help of
> qcom_pcie_config_sid_1_9_0() function for SoCs supporting the 1_9_0 config.
> 
> But With newer Qcom SoCs starting from SM8450, BDF to SID translation is
> set to bypass mode by default in hardware. Due to this, the translation
> table that is set in the qcom_pcie_config_sid_1_9_0() is essentially
> unused and the default SID is used for all endpoints in SoCs starting from
> SM8450.
> 
> This is a security concern and also warrants swapping the DeviceID in DT
> while using the GIC ITS to handle MSIs from endpoints. The swapping is
> currently done like below in DT when using GIC ITS:
> 
> 			/*
> 			 * MSIs for BDF (1:0.0) only works with Device ID 0x5980.
> 			 * Hence, the IDs are swapped.
> 			 */
> 			msi-map = <0x0 &gic_its 0x5981 0x1>,
> 				  <0x100 &gic_its 0x5980 0x1>;
> 
> Here, swapping of the DeviceIDs ensure that the endpoint with BDF (1:0.0)
> gets the DeviceID 0x5980 which is associated with the default SID as per
> the iommu mapping in DT. So MSIs were delivered with IDs swapped so far.
> But this also means the Root Port (0:0.0) won't receive any MSIs (for PME,
> AER etc...)
> 
> So let's fix these issues by clearing the BDF to SID bypass mode for all
> SoCs making use of the 1_9_0 config. This allows the PCIe devices to use
> the correct SID, thus avoiding the DeviceID swapping hack in DT and also
> achieving the isolation between devices.
> 
> Cc:  <stable@...r.kernel.org> # 5.11
> Fixes: 4c9398822106 ("PCI: qcom: Add support for configuring BDF to SID mapping for SM8250")
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> ---

Looks sensible..

Does switching away from bypass show any performance degradation?

Konrad