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Commit 7ac77099 authored by Avi Kivity's avatar Avi Kivity
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KVM: Prevent internal slots from being COWed 



If a process with a memory slot is COWed, the page will change its address
(despite having an elevated reference count).  This breaks internal memory
slots which have their physical addresses loaded into vmcs registers (see
the APIC access memory slot).

Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
parent e36d96f7

arch/x86/kvm/x86.c

+6 −1
Original line number Diff line number Diff line
@@ -5491,6 +5491,11 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm, 
				int user_alloc)

{

	int npages = memslot->npages;

	int map_flags = MAP_PRIVATE | MAP_ANONYMOUS;



	/* Prevent internal slot pages from being moved by fork()/COW. */

	if (memslot->id >= KVM_MEMORY_SLOTS)

		map_flags = MAP_SHARED | MAP_ANONYMOUS;



	/*To keep backward compatibility with older userspace,

	 *x86 needs to hanlde !user_alloc case.
@@ -5503,7 +5508,7 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm, 
			userspace_addr = do_mmap(NULL, 0,

						 npages * PAGE_SIZE,

						 PROT_READ | PROT_WRITE,

						 MAP_PRIVATE | MAP_ANONYMOUS,

						 map_flags,

						 0);

			up_write(&current->mm->mmap_sem);