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| author | Sean Christopherson <seanjc@google.com> | 2024-06-13 12:01:03 -0700 |
|---|---|---|
| committer | Sean Christopherson <seanjc@google.com> | 2024-06-28 08:55:00 -0700 |
| commit | cb9fb5fc12ef8a7c5129c7db0f80df45726b8dcd (patch) | |
| tree | d15ced94df6bb5aca8fc17aa573fa02e1dbfe5a9 | |
| parent | 02b0d3b9d4dd1ef76b3e8c63175f1ae9ff392313 (diff) | |
| download | linux-stable-cb9fb5fc12ef8a7c5129c7db0f80df45726b8dcd.tar.gz linux-stable-cb9fb5fc12ef8a7c5129c7db0f80df45726b8dcd.tar.bz2 linux-stable-cb9fb5fc12ef8a7c5129c7db0f80df45726b8dcd.zip | |
KVM: nVMX: Update VMCS12_REVISION comment to state it should never change
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>
| -rw-r--r-- | arch/x86/kvm/vmx/vmcs12.h | 14 |
1 files changed, 8 insertions, 6 deletions
diff --git a/arch/x86/kvm/vmx/vmcs12.h b/arch/x86/kvm/vmx/vmcs12.h index 01936013428b..56fd150a6f24 100644 --- a/arch/x86/kvm/vmx/vmcs12.h +++ b/arch/x86/kvm/vmx/vmcs12.h @@ -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) |