Hi, apologies if I am not posting to the appropriate list(s).
I am using QEMU-KVM and try to implement a simple character device which
offers mmap() functionality of host device memory to guest userspace.
For this purpose, I have written a dummy guest driver which communicates
with a qemu backend device.
Specifically, the guest driver allocates a page and passes the
associated address to qemu, which then translates it to host virtual
address (cpu_physical_memory_map()). It then calls mmap() with MAP_FIXED
and this host virtual address, which succeeds, and sends back the
response.
The problem arises here, when guest (either in kernespace or in
userspace via remap_pfn_range()) tries to access the relevant address
and faults with EPT. The path goes to handle_ept_violation() in kvm
module and eventually BUG_ON() is triggered at:
virt/kvm/kvm_main.c:1252 (version 3.16):
-- cut here --
pfn = ((addr - vma->vm_start) >> PAGE_SHIFT) +
vma->vm_pgoff;
BUG_ON(!kvm_is_mmio_pfn(pfn));
-- cut here --
addr == vma->vm_start and pfn is assigned the value of vma->vm_pgoff !!
What am I missing here? Is this scenario invalid? Can you please shed
some light?
Thanks in advance!
--Stefanos
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