FAILED: patch "[PATCH] KVM: nSVM: Add missing consistency check for EFER, CR0, CR4," failed to apply to 5.10-stable tree

The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.10.y
git checkout FETCH_HEAD
git cherry-pick -x 96bd3e76a171a8e21a6387e54e4c420a81968492
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026050344-throwback-dilation-fc45@gregkh' --subject-prefix 'PATCH 5.10.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 96bd3e76a171a8e21a6387e54e4c420a81968492 Mon Sep 17 00:00:00 2001
From: Yosry Ahmed <[email protected]>
Date: Tue, 3 Mar 2026 00:34:10 +0000
Subject: [PATCH] KVM: nSVM: Add missing consistency check for EFER, CR0, CR4,
and CS
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

According to the APM Volume #2, 15.5, Canonicalization and Consistency Checks (24593—Rev. 3.42—March 2024), the following condition (among others) results in a #VMEXIT with VMEXIT_INVALID (aka SVM_EXIT_ERR):

EFER.LME, CR0.PG, CR4.PAE, CS.L, and CS.D are all non-zero.

In the list of consistency checks done when EFER.LME and CR0.PG are set, add a check that CS.L and CS.D are not both set, after the existing check that CR4.PAE is set.

This is functionally a nop because the nested VMRUN results in SVM_EXIT_ERR in HW, which is forwarded to L1, but KVM makes all consistency checks before a VMRUN is actually attempted.

index a59b976c16db..50180565bcfc 100644
@@ -391,6 +391,10 @@ static bool nested_vmcb_check_save(struct kvm_vcpu *vcpu,
 		    CC(!(save->cr0 & X86_CR0_PE)) ||
 		    CC(!kvm_vcpu_is_legal_cr3(vcpu, save->cr3)))
 			return false;
+
+		if (CC((save->cs.attrib & SVM_SELECTOR_L_MASK) &&
+		       (save->cs.attrib & SVM_SELECTOR_DB_MASK)))
+			return false;
 	}
 
 	/* Note, SVM doesn't have any additional restrictions on CR4. */

@@ -486,6 +490,8 @@ static void __nested_copy_vmcb_save_to_cache(struct vmcb_save_area_cached *to,
 	 * Copy only fields that are validated, as we need them
 	 * to avoid TOC/TOU races.
 	 */
+	to->cs = from->cs;
+
 	to->efer = from->efer;
 	to->cr0 = from->cr0;
 	to->cr3 = from->cr3;

index 7629cb37c930..0a5d5a4453b7 100644
@@ -140,6 +140,7 @@ struct kvm_vmcb_info {
 };
 
 struct vmcb_save_area_cached {
+	struct vmcb_seg cs;
 	u64 efer;
 	u64 cr4;
 	u64 cr3;