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Subject[PATCH] KVM: arm: remove excessive permission check in kvm_arch_prepare_memory_region
In kvm_arch_prepare_memory_region, arm kvm regards the memory region as
writable if the flag has no KVM_MEM_READONLY, and the vm is readonly if

But there is common usage for setting kvm memory region as follows:
e.g. qemu side (see the PROT_NONE flag)
2. re mmap the above area with read/write authority.

Such example is used in virtio-fs qemu codes which hasn't been upstreamed
[1]. But seems we can't forbid this example.

Without this patch, it will cause an EPERM during kvm_set_memory_region()
and cause qemu boot crash.

As told by Ard, "the underlying assumption is incorrect, i.e., that the
value of vm_flags at this point in time defines how the VMA is used
during its lifetime. There may be other cases where a VMA is created
with VM_READ vm_flags that are changed to VM_READ|VM_WRITE later, and
we are currently rejecting this use case as well."


Cc: Ard Biesheuvel <>
Suggested-by: Ard Biesheuvel <>
Signed-off-by: Jia He <>
virt/kvm/arm/mmu.c | 9 ---------
1 file changed, 9 deletions(-)

diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
index 38b4c910b6c3..a48994af70b8 100644
--- a/virt/kvm/arm/mmu.c
+++ b/virt/kvm/arm/mmu.c
@@ -2301,15 +2301,6 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
if (!vma || vma->vm_start >= reg_end)

- /*
- * Mapping a read-only VMA is only allowed if the
- * memory region is configured as read-only.
- */
- if (writable && !(vma->vm_flags & VM_WRITE)) {
- ret = -EPERM;
- break;
- }
* Take the intersection of this VMA with the memory region
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