AMD Ryzen could have problems in the PnP PCI controller

AMD Ryzen processors reportedly have a hidden feature that would create unexpected operation of the PnP PCI controller. Although it seems that this parameter has no real impact on performance, it has caused quite a stir.

PnP PCI controller malfunction detected on AMD Ryzen processors

There is little to no doubt about how good AMD Ryzen processors are. These processors have greatly improved their performance since their release and have become increasingly popular. They offer excellent performance at a really interesting price point, which poses problems for Intel.

Alex Ionescu reportedly discovered an unexpected performance in the PnP PCI controller over the weekend and posted it on Twitter. Specifically, the PCI driver in Windows was found to be performing a search for 19 hash processes (.exe files) that would represent 19 games.

When the driver detects one of the searched applications, it seems to disable some functions via a model-specific register (SMR) of the processor.

It appears that on Ryzen 1000 processors (and possibly Ryzen 2000 processors), some instruction cache functions are affected. On Ryzen 3000 processors, certain L1 and L2 cache issues are reportedly occurring. Such adjustments would not occur on AMD Ryzen 5000 processors.

Ionescu initially assumed that it would bring performance improvements, but in reality, it could lead to stability issues for the 19 affected applications. Such performance optimization is heavily hidden in the PCI driver.

Information that would remain hidden and undocumented

The bit that adjusts the driver in the MSR and the function in the driver are not documented by AMD, according to Ionescu. He also criticizes the fact that this driver has received WHQL certification from Microsoft, even though it performs different functions in the background than one would expect.

This PCI driver should be focused on achieving the WHQL target, which should provide improved system stability. This hidden function would not provide confidence in the operation of this driver.

In addition, there appears to be a security issue. The ioctl interface in the driver would have allowed Ionescu to crash the computer by injecting just one line of code with PowerShell. It is also possible to manipulate the list of processes monitored by the driver.

We are not currently aware that AMD has commented on this issue, and it is possible that this will take some time. It would be normal for them to analyze the information provided by Ionescu before giving any information. It is not excluded that this is some kind of bug in the driver and can be fixed with a patch or update.

Source

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