linux-kernel - [PATCH 6.6.y 11/20] KVM: x86: Move handling of is_guest

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250815002540.2375664-12-seanjc@google.com>
Date: Thu, 14 Aug 2025 17:25:31 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: stable@...r.kernel.org, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Sasha Levin <sashal@...nel.org>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 6.6.y 11/20] KVM: x86: Move handling of is_guest_mode() into
 fastpath exit handlers

[ Upstream commit bf1a49436ea37b98dd2f37c57608951d0e28eecc ]

Let the fastpath code decide which exits can/can't be handled in the
fastpath when L2 is active, e.g. when KVM generates a VMX preemption
timer exit to forcefully regain control, there is no "work" to be done and
so such exits can be handled in the fastpath regardless of whether L1 or
L2 is active.

Moving the is_guest_mode() check into the fastpath code also makes it
easier to see that L2 isn't allowed to use the fastpath in most cases,
e.g. it's not immediately obvious why handle_fastpath_preemption_timer()
is called from the fastpath and the normal path.

Link: https://lore.kernel.org/r/20240110012705.506918-5-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/svm/svm.c | 6 +++---
 arch/x86/kvm/vmx/vmx.c | 6 +++---
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 5a230be224d1..f42c6ef7dc20 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4157,6 +4157,9 @@ static int svm_vcpu_pre_run(struct kvm_vcpu *vcpu)
 
 static fastpath_t svm_exit_handlers_fastpath(struct kvm_vcpu *vcpu)
 {
+	if (is_guest_mode(vcpu))
+		return EXIT_FASTPATH_NONE;
+
 	if (to_svm(vcpu)->vmcb->control.exit_code == SVM_EXIT_MSR &&
 	    to_svm(vcpu)->vmcb->control.exit_info_1)
 		return handle_fastpath_set_msr_irqoff(vcpu);
@@ -4315,9 +4318,6 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu,
 
 	svm_complete_interrupts(vcpu);
 
-	if (is_guest_mode(vcpu))
-		return EXIT_FASTPATH_NONE;
-
 	return svm_exit_handlers_fastpath(vcpu);
 }
 
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 631fdd4a575a..4c991d514015 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7258,6 +7258,9 @@ void noinstr vmx_spec_ctrl_restore_host(struct vcpu_vmx *vmx,
 
 static fastpath_t vmx_exit_handlers_fastpath(struct kvm_vcpu *vcpu)
 {
+	if (is_guest_mode(vcpu))
+		return EXIT_FASTPATH_NONE;
+
 	switch (to_vmx(vcpu)->exit_reason.basic) {
 	case EXIT_REASON_MSR_WRITE:
 		return handle_fastpath_set_msr_irqoff(vcpu);
@@ -7468,9 +7471,6 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu, bool force_immediate_exit)
 	vmx_recover_nmi_blocking(vmx);
 	vmx_complete_interrupts(vmx);
 
-	if (is_guest_mode(vcpu))
-		return EXIT_FASTPATH_NONE;
-
 	return vmx_exit_handlers_fastpath(vcpu);
 }
 
-- 
2.51.0.rc1.163.g2494970778-goog