Patch "Revert "nSVM: Check for reserved encodings of TLB_CONTROL in nested VMCB"" has been added to the 6.1-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

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

to the 6.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     revert-nsvm-check-for-reserved-encodings-of-tlb_cont.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 1fad458de7b2324a442126e1efff828628edbb70
Author: Sean Christopherson <seanjc@xxxxxxxxxx>
Date:   Wed Oct 18 12:41:03 2023 -0700

    Revert "nSVM: Check for reserved encodings of TLB_CONTROL in nested VMCB"
    
    [ Upstream commit a484755ab2526ebdbe042397cdd6e427eb4b1a68 ]
    
    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@xxxxxxxxxxx>
    Closes: https://lkml.kernel.org/r/b9915c9c-4cf6-051a-2d91-44cc6380f455%40proxmox.com
    Cc: stable@xxxxxxxxxxxxxxx
    Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20231018194104.1896415-2-seanjc@xxxxxxxxxx
    Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index bc288e6bde64..5d4d78c9a787 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -239,18 +239,6 @@ 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)
 {
@@ -270,8 +258,6 @@ 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;
 
 	return true;
 }