iommu/vt-d: Disallow dirty tracking if incoherent page walk

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: iommu/vt-d: Disallow dirty tracking if incoherent page walk Dirty page tracking relies on the IOMMU atomically updating the dirty bit in the paging-structure entry. For this operation to succeed, the paging- structure memory must be coherent between the IOMMU and the CPU. In another word, if the iommu page walk is incoherent, dirty page tracking doesn't work. The Intel VT-d specification, Section 3.10 "Snoop Behavior" states: "Remapping hardware encountering the need to atomically update A/EA/D bits in a paging-structure entry that is not snooped will result in a non- recoverable fault." To prevent an IOMMU from being incorrectly configured for dirty page tracking when it is operating in an incoherent mode, mark SSADS as supported only when both ecap_slads and ecap_smpwc are supported.

References

• https://git.kernel.org/stable/c/ebe16d245a00626bb87163862a1b07daf5475a3e
• https://git.kernel.org/stable/c/8d096ce0e87bdc361f0b25d7943543bc53aa0b9e
• https://git.kernel.org/stable/c/57f55048e564dedd8a4546d018e29d6bbfff0a7e