Revert "nSVM: Check for reserved encodings of TLB_CONTROL in nested VMCB"

Revert KVM's made-up consistency check on SVM's TLB control.  The APM says
that unsupported encodings are reserved, but the APM doesn't state that
VMRUN checks for a supported encoding.  Unless something is called out
in "Canonicalization and Consistency Checks" or listed as MBZ (Must Be
Zero), AMD behavior is typically to let software shoot itself in the foot.

This reverts commit 174a921b6975ef959dd82ee9e8844067a62e3ec1.

Fixes: 174a921b6975 ("nSVM: Check for reserved encodings of TLB_CONTROL in nested VMCB")
Reported-by: Stefan Sterz <s.sterz@proxmox.com>
Closes: https://lkml.kernel.org/r/b9915c9c-4cf6-051a-2d91-44cc6380f455%40proxmox.com
Cc: stable@vger.kernel.org
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Link: https://lore.kernel.org/r/20231018194104.1896415-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 3fea8c47679e6899742c6f5aa08046da041439a2..60891b9ce25f61ef509f7af4a2cc1fb736bced3d 100644 (file)
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -247,18 +247,6 @@ static bool nested_svm_check_bitmap_pa(struct kvm_vcpu *vcpu, u64 pa, u32 size)
            kvm_vcpu_is_legal_gpa(vcpu, addr + size - 1);
 }
 
-static bool nested_svm_check_tlb_ctl(struct kvm_vcpu *vcpu, u8 tlb_ctl)
-{
-       /* Nested FLUSHBYASID is not supported yet.  */
-       switch(tlb_ctl) {
-               case TLB_CONTROL_DO_NOTHING:
-               case TLB_CONTROL_FLUSH_ALL_ASID:
-                       return true;
-               default:
-                       return false;
-       }
-}
-
 static bool __nested_vmcb_check_controls(struct kvm_vcpu *vcpu,
                                         struct vmcb_ctrl_area_cached *control)
 {
@@ -278,9 +266,6 @@ static bool __nested_vmcb_check_controls(struct kvm_vcpu *vcpu,
                                           IOPM_SIZE)))
                return false;
 
-       if (CC(!nested_svm_check_tlb_ctl(vcpu, control->tlb_ctl)))
-               return false;
-
        if (CC((control->int_ctl & V_NMI_ENABLE_MASK) &&
               !vmcb12_is_intercept(control, INTERCEPT_NMI))) {
                return false;