From 7ac77099ce88a0c31b75acd0ec5ef3da4415a6d8 Mon Sep 17 00:00:00 2001 From: Avi Kivity Date: Mon, 21 Jun 2010 10:57:45 +0300 Subject: [PATCH] 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: Avi Kivity --- arch/x86/kvm/x86.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 7ef4410..68be38e 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -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(¤t->mm->mmap_sem); -- 2.7.4