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

[Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>]

On Thu, Mar 07, 2024 at 12:19:56PM +0100, Konrad Dybcio wrote:
> 
> 
> 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@vger.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@linaro.org>
> > ---
> 
> Looks sensible..
> 
> Does switching away from bypass show any performance degradation?
> 

Not at all with my throughput test on SM8450 dev board. But there shouldn't be
any performance related issue since we are just forcing the hw to use a
different SID (correct one) than the default one.

- Mani

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