KVM: VMX: conditionally disable 2M pages

Disable usage of 2M pages if VMX_EPT_2MB_PAGE_BIT (bit 16) is clear
in MSR_IA32_VMX_EPT_VPID_CAP and EPT is enabled.

[avi: s/largepages_disabled/largepages_enabled/ to avoid negative logic]

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

3 files changed, 16 insertions, 2 deletions

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 94c07ada103e..fc8d49c6bc51 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -1381,6 +1381,9 @@ static __init int hardware_setup(void)
         if (!cpu_has_vmx_tpr_shadow())
                 kvm_x86_ops->update_cr8_intercept = NULL;
 
+        if (enable_ept && !cpu_has_vmx_ept_2m_page())
+                kvm_disable_largepages();
+
         return alloc_kvm_area();
 }
 
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index c6e4d02067fe..6988858dc56e 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -224,6 +224,7 @@ int kvm_arch_set_memory_region(struct kvm *kvm,
                                 struct kvm_userspace_memory_region *mem,
                                 struct kvm_memory_slot old,
                                 int user_alloc);
+void kvm_disable_largepages(void);
 void kvm_arch_flush_shadow(struct kvm *kvm);
 gfn_t unalias_gfn(struct kvm *kvm, gfn_t gfn);
 struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 777fe533cfe7..48d5e697bf44 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -85,6 +85,8 @@ static long kvm_vcpu_ioctl(struct file *file, unsigned int ioctl,
 
 static bool kvm_rebooting;
 
+static bool largepages_enabled = true;
+
 #ifdef KVM_CAP_DEVICE_ASSIGNMENT
 static struct kvm_assigned_dev_kernel *kvm_find_assigned_dev(struct list_head *head,
                                                       int assigned_dev_id)
@@ -1174,9 +1176,11 @@ int __kvm_set_memory_region(struct kvm *kvm,
                 ugfn = new.userspace_addr >> PAGE_SHIFT;
                 /*
                  * If the gfn and userspace address are not aligned wrt each
-                 * other, disable large page support for this slot
+                 * other, or if explicitly asked to, disable large page
+                 * support for this slot
                  */
-                if ((base_gfn ^ ugfn) & (KVM_PAGES_PER_HPAGE - 1))
+                if ((base_gfn ^ ugfn) & (KVM_PAGES_PER_HPAGE - 1) ||
+                    !largepages_enabled)
                         for (i = 0; i < largepages; ++i)
                                 new.lpage_info[i].write_count = 1;
         }
@@ -1291,6 +1295,12 @@ out:
         return r;
 }
 
+void kvm_disable_largepages(void)
+{
+        largepages_enabled = false;
+}
+EXPORT_SYMBOL_GPL(kvm_disable_largepages);
+
 int is_error_page(struct page *page)
 {
         return page == bad_page;