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arm: KVM: Fix incorrect device to IPA mapping

A critical bug has been found in device memory stage1 translation for
VMs with more then 4GB of address space. Once vm_pgoff size is smaller
then pa (which is true for LPAE case, u32 and u64 respectively) some
more significant bits of pa may be lost as a shift operation is performed
on u32 and later cast onto u64.

Example: vm_pgoff(u32)=0x00210030, PAGE_SHIFT=12
        expected pa(u64):   0x0000002010030000
        produced pa(u64):   0x0000000010030000

The fix is to change the order of operations (casting first onto phys_addr_t
and then shifting).

Reviewed-by: Marc Zyngier <>
[maz: fixed changelog and patch formatting]
Signed-off-by: Marek Majtyka <>
Signed-off-by: Marc Zyngier <>
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alardam authored and Marc Zyngier committed Sep 16, 2015
1 parent 1713e5a commit ca09f02f122b2ecb0f5ddfc5fd47b29ed657d4fd
Showing with 4 additions and 2 deletions.
  1. +4 −2 arch/arm/kvm/mmu.c
@@ -1792,8 +1792,10 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
if (vma->vm_flags & VM_PFNMAP) {
gpa_t gpa = mem->guest_phys_addr +
(vm_start - mem->userspace_addr);
phys_addr_t pa = (vma->vm_pgoff << PAGE_SHIFT) +
vm_start - vma->vm_start;
phys_addr_t pa;

pa = (phys_addr_t)vma->vm_pgoff << PAGE_SHIFT;
pa += vm_start - vma->vm_start;

/* IO region dirty page logging not allowed */
if (memslot->flags & KVM_MEM_LOG_DIRTY_PAGES)

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