Linux Kernels

KVM: nVMX: Restore the VMCS12 offsets for v4.0 fields

This change “KVM: nVMX: Restore the VMCS12 offsets for v4.0 fields” (commit b348e79) in Linux kernel is authored by Jim Mattson <jmattson [at]> on Tue May 1 15:40:27 2018 -0700.

Description of "KVM: nVMX: Restore the VMCS12 offsets for v4.0 fields"

The change “KVM: nVMX: Restore the VMCS12 offsets for v4.0 fields” introduces changes as follows.

KVM: nVMX: Restore the VMCS12 offsets for v4.0 fields

Changing the VMCS12 layout will break save/restore compatibility with
older kvm releases once the KVM_{GET,SET}_NESTED_STATE ioctls are
accepted upstream. Google has already been using these ioctls for some
time, and we implore the community not to disturb the existing layout.

Move the four most recently added fields to preserve the offsets of
the previously defined fields and reserve locations for the vmread and
vmwrite bitmaps, which will be used in the virtualization of VMCS
shadowing (to improve the performance of double-nesting).

Signed-off-by: Jim Mattson <>
Reviewed-by: Konrad Rzeszutek Wilk <>
[Kept the SDM order in vmcs_field_to_offset_table. - Radim]
Signed-off-by: Radim Krčmář <>

Linux kernel releases containing commit b348e79

The Linux kernel releases containing this commit are as follows.

Linux kernel code changes in "KVM: nVMX: Restore the VMCS12 offsets for v4.0 fields"

There are 27 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 arch/x86/include/asm/vmx.h |  2 ++
 arch/x86/kvm/vmx.c         | 25 ++++++++++++++++++-------
 2 files changed, 20 insertions(+), 7 deletions(-)
diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
index 5db8b0b10766..425e6b8b9547 100644
--- a/arch/x86/include/asm/vmx.h
+++ b/arch/x86/include/asm/vmx.h
@@ -207,7 +207,9 @@ enum vmcs_field {
 	EPTP_LIST_ADDRESS               = 0x00002024,
 	EPTP_LIST_ADDRESS_HIGH          = 0x00002025,
 	VMREAD_BITMAP                   = 0x00002026,
+	VMREAD_BITMAP_HIGH              = 0x00002027,
 	VMWRITE_BITMAP                  = 0x00002028,
+	VMWRITE_BITMAP_HIGH             = 0x00002029,
 	XSS_EXIT_BITMAP                 = 0x0000202C,
 	XSS_EXIT_BITMAP_HIGH            = 0x0000202D,
 	TSC_MULTIPLIER                  = 0x00002032,
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 95c05581a06f..722026c9d478 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -242,7 +242,11 @@ struct shared_msr_entry {
  * underlying hardware which will be used to run L2.
  * This structure is packed to ensure that its layout is identical across
  * machines (necessary for live migration).
- * If there are changes in this struct, VMCS12_REVISION must be changed.
+ *
+ * IMPORTANT: Changing the layout of existing fields in this structure
+ * will break save/restore compatibility with older kvm releases. When
+ * adding new fields, either use space in the reserved padding* arrays
+ * or add the new fields to the end of the structure.
 typedef u64 natural_width;
 struct __packed vmcs12 {
@@ -265,17 +269,14 @@ struct __packed vmcs12 {
 	u64 virtual_apic_page_addr;
 	u64 apic_access_addr;
 	u64 posted_intr_desc_addr;
-	u64 vm_function_control;
 	u64 ept_pointer;
 	u64 eoi_exit_bitmap0;
 	u64 eoi_exit_bitmap1;
 	u64 eoi_exit_bitmap2;
 	u64 eoi_exit_bitmap3;
-	u64 eptp_list_address;
 	u64 xss_exit_bitmap;
 	u64 guest_physical_address;
 	u64 vmcs_link_pointer;
-	u64 pml_address;
 	u64 guest_ia32_debugctl;
 	u64 guest_ia32_pat;
 	u64 guest_ia32_efer;
@@ -288,7 +289,12 @@ struct __packed vmcs12 {
 	u64 host_ia32_pat;
 	u64 host_ia32_efer;
 	u64 host_ia32_perf_global_ctrl;
-	u64 padding64[8]; /* room for future expansion */
+	u64 vmread_bitmap;
+	u64 vmwrite_bitmap;
+	u64 vm_function_control;
+	u64 eptp_list_address;
+	u64 pml_address;
+	u64 padding64[3]; /* room for future expansion */
 	 * To allow migration of L1 (complete with its L2 guests) between
 	 * machines of different natural widths (32 or 64 bit), we cannot have
@@ -397,7 +403,6 @@ struct __packed vmcs12 {
 	u16 guest_ldtr_selector;
 	u16 guest_tr_selector;
 	u16 guest_intr_status;
-	u16 guest_pml_index;
 	u16 host_es_selector;
 	u16 host_cs_selector;
 	u16 host_ss_selector;
@@ -405,12 +410,16 @@ struct __packed vmcs12 {
 	u16 host_fs_selector;
 	u16 host_gs_selector;
 	u16 host_tr_selector;
+	u16 guest_pml_index;
  * VMCS12_REVISION is an arbitrary id that should be changed if the content or
  * layout of struct vmcs12 is changed. MSR_IA32_VMX_BASIC returns this id, and
  * VMPTRLD verifies that the VMCS region that L1 is loading contains this id.
+ *
+ * IMPORTANT: Changing this value will break save/restore compatibility with
+ * older kvm releases.
 #define VMCS12_REVISION 0x11e57ed0
@@ -762,6 +771,7 @@ static const unsigned short vmcs_field_to_offset_table[] = {
 	FIELD64(VM_EXIT_MSR_STORE_ADDR, vm_exit_msr_store_addr),
 	FIELD64(VM_EXIT_MSR_LOAD_ADDR, vm_exit_msr_load_addr),
 	FIELD64(VM_ENTRY_MSR_LOAD_ADDR, vm_entry_msr_load_addr),
+	FIELD64(PML_ADDRESS, pml_address),
 	FIELD64(TSC_OFFSET, tsc_offset),
 	FIELD64(VIRTUAL_APIC_PAGE_ADDR, virtual_apic_page_addr),
 	FIELD64(APIC_ACCESS_ADDR, apic_access_addr),
@@ -773,10 +783,11 @@ static const unsigned short vmcs_field_to_offset_table[] = {
 	FIELD64(EOI_EXIT_BITMAP2, eoi_exit_bitmap2),
 	FIELD64(EOI_EXIT_BITMAP3, eoi_exit_bitmap3),
 	FIELD64(EPTP_LIST_ADDRESS, eptp_list_address),
+	FIELD64(VMREAD_BITMAP, vmread_bitmap),
+	FIELD64(VMWRITE_BITMAP, vmwrite_bitmap),
 	FIELD64(XSS_EXIT_BITMAP, xss_exit_bitmap),
 	FIELD64(GUEST_PHYSICAL_ADDRESS, guest_physical_address),
 	FIELD64(VMCS_LINK_POINTER, vmcs_link_pointer),
-	FIELD64(PML_ADDRESS, pml_address),
 	FIELD64(GUEST_IA32_DEBUGCTL, guest_ia32_debugctl),
 	FIELD64(GUEST_IA32_PAT, guest_ia32_pat),
 	FIELD64(GUEST_IA32_EFER, guest_ia32_efer),

The commit for this change in Linux stable tree is b348e79 (patch).

Last modified: 2020/01/11 06:42