kevin/linux
1
Fork 0
Code

KVM: nVMX: Update VMCS12_REVISION comment to state it should never change

Browse Source 
Rewrite the comment above VMCS12_REVISION to unequivocally state that the
ID must never change.  KVM_{G,S}ET_NESTED_STATE have been officially
supported for some time now, i.e. changing VMCS12_REVISION would break
userspace.

Opportunistically add a blurb to the CHECK_OFFSET() comment to make it
explicitly clear that new fields are allowed, i.e. that the restriction
on the layout is all about backwards compatibility.

No functional change intended.

Cc: Jim Mattson <jmattson@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Link: https://lore.kernel.org/r/20240613190103.1054877-1-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2024-06-13 12:01:03 -07:00
parent 02b0d3b9d4
commit cb9fb5fc12
1 changed files with 8 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
arch/x86/kvm/vmx/vmcs12.h
View File

@ -188,12 +188,13 @@ struct __packed vmcs12 {
};
/*
* 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.
* VMCS12_REVISION is KVM's arbitrary ID for the layout of struct vmcs12. KVM
* enumerates this value to L1 via MSR_IA32_VMX_BASIC, and checks the revision
* ID during nested VMPTRLD to verify that L1 is loading a VMCS that adhere's
* to KVM's virtual CPU definition.
*
* IMPORTANT: Changing this value will break save/restore compatibility with
* older kvm releases.
* DO NOT change this value, as it will break save/restore compatibility with
* older KVM releases.
*/
#define VMCS12_REVISION 0x11e57ed0
@ -206,7 +207,8 @@ struct __packed vmcs12 {
#define VMCS12_SIZE KVM_STATE_NESTED_VMX_VMCS_SIZE
/*
* For save/restore compatibility, the vmcs12 field offsets must not change.
* For save/restore compatibility, the vmcs12 field offsets must not change,
* although appending fields and/or filling gaps is obviously allowed.
*/
#define CHECK_OFFSET(field, loc) \
ASSERT_STRUCT_OFFSET(struct vmcs12, field, loc)