From 7f586f7b615d9e13d5f62a73778f4c54c50dfa56 Mon Sep 17 00:00:00 2001
From: Glauber Costa <glommer@redhat.com>
Date: Wed, 23 Jun 2010 13:51:13 -0300
Subject: [PATCH 2/2] KVM: Prevent internal slots from being COWed

RH-Author: Glauber Costa <glommer@redhat.com>
Message-id: <patch-10116-clone-for-rhel5-rhel56>
Patchwork-id: 10141
O-Subject: [RHEL5.6/z patch 2/2] KVM: Prevent internal slots from being COWed
Bugzilla: 606953
RH-Acked-by: Avi Kivity <avi@redhat.com>
RH-Acked-by: Jes Sorensen <Jes.Sorensen@redhat.com>
RH-Acked-by: Gleb Natapov <gleb@redhat.com>

RH-Bugzilla: 606953
RH-Upstream-status: kvm/master

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 <avi@redhat.com>
Signed-off-by: Glauber Costa <glommer@redhat.com>
---
 arch/x86/kvm/x86.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
---
 arch/x86/kvm/x86.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 363141c..9a613cb 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4700,6 +4700,11 @@ int kvm_arch_set_memory_region(struct kvm *kvm,
 {
 	int npages = mem->memory_size >> PAGE_SHIFT;
 	struct kvm_memory_slot *memslot = &kvm->memslots[mem->slot];
+	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.
@@ -4712,7 +4717,7 @@ int kvm_arch_set_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);
 
-- 
1.7.0.3