[Xen-devel] Trapping I/O accesses of a driver domain

["Olatunji Ruwase" <oor@xxxxxxxxxx>]

Hi,
 I am a graduate student working on dynamic correctness checking of kernel
 mode device drivers. I want to detect/trap accesses from a Linux driver
 to device accessible locations (e.g ioremap'd, dma_* locations), and
 I am exploring the possibility of using Xen for this. I am using x86 PV
 Xen-3.3 with a dom0 and driver domU both running linux-2.6.18-xen. For
 various reasons HVM Xen is not suitable for my work.

 The idea is to use page faults to detect the I/O accesses of the driver
 by marking the affected pages not present in the page tables. For
 ioremap'd pages, this seems pretty straightforward since the ptes are
 marked with _PAGE_IO before they are passed to Xen. And so it seems
 modifying do_mmu_update () to detect and mark such ptes not present should
 work. Is this a reasonable approach ?.

 Detecting accesses to dma mapped (dma_alloc_coherent, dma_map_single)
 locations seems more difficult because, as far as I can tell there is no
 hypercall informing Xen that the locations are used for I/O. I am probably
 misunderstanding how this works and would appreciate clarifications.

 Thank you,

tunji








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