swiotlb-xen: SWIOTLB library for Xen PV guest with PCI passthrough.
This patchset: PV guests under Xen are running in an non-contiguous memory architecture. When PCI pass-through is utilized, this necessitates an IOMMU for translating bus (DMA) to virtual and vice-versa and also providing a mechanism to have contiguous pages for device drivers operations (say DMA operations). Specifically, under Xen the Linux idea of pages is an illusion. It assumes that pages start at zero and go up to the available memory. To help with that, the Linux Xen MMU provides a lookup mechanism to translate the page frame numbers (PFN) to machine frame numbers (MFN) and vice-versa. The MFN are the "real" frame numbers. Furthermore memory is not contiguous. Xen hypervisor stitches memory for guests from different pools, which means there is no guarantee that PFN==MFN and PFN+1==MFN+1. Lastly with Xen 4.0, pages (in debug mode) are allocated in descending order (high to low), meaning the guest might never get any MFN's under the 4GB mark. Signed-off-by: Konrad Rzeszutek Wilk <email@example.com> Acked-by: Jeremy Fitzhardinge <firstname.lastname@example.org> Cc: FUJITA Tomonori <email@example.com> Cc: Albert Herranz <firstname.lastname@example.org> Cc: Ian Campbell <Ian.Campbell@citrix.com>
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