linux-kernel - [PATCH v2 6/8] KVM: SVM: restore host save area from assembly

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Message-Id: <20221108151532.1377783-7-pbonzini@redhat.com>
Date:   Tue,  8 Nov 2022 10:15:30 -0500
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     nathan@...nel.org, thomas.lendacky@....com,
        andrew.cooper3@...rix.com, peterz@...radead.org,
        jmattson@...gle.com, seanjc@...gle.com, stable@...r.kernel.org
Subject: [PATCH v2 6/8] KVM: SVM: restore host save area from assembly

This is needed so that FILL_RETURN_BUFFER has access to the
percpu area via the GS segment base.

Cc: stable@...r.kernel.org
Fixes: f14eec0a3203 ("KVM: SVM: move more vmentry code to assembly")
Reported-by: Nathan Chancellor <nathan@...nel.org>
Analyzed-by: Andrew Cooper <andrew.cooper3@...rix.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/svm/svm.c     |  3 +--
 arch/x86/kvm/svm/svm.h     |  2 +-
 arch/x86/kvm/svm/svm_ops.h |  5 -----
 arch/x86/kvm/svm/vmenter.S | 13 +++++++++++++
 4 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 0ba4feb19cb6..e15f6ea9e5cc 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3922,8 +3922,7 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu)
 	} else {
 		struct svm_cpu_data *sd = per_cpu(svm_data, vcpu->cpu);
 
-		__svm_vcpu_run(svm);
-		vmload(__sme_page_pa(sd->save_area));
+		__svm_vcpu_run(svm, __sme_page_pa(sd->save_area));
 	}
 
 	guest_state_exit_irqoff();
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 7ff1879e73c5..932f26be5675 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -684,6 +684,6 @@ void sev_es_unmap_ghcb(struct vcpu_svm *svm);
 /* vmenter.S */
 
 void __svm_sev_es_vcpu_run(struct vcpu_svm *svm);
-void __svm_vcpu_run(struct vcpu_svm *svm);
+void __svm_vcpu_run(struct vcpu_svm *svm, unsigned long hsave_pa);
 
 #endif
diff --git a/arch/x86/kvm/svm/svm_ops.h b/arch/x86/kvm/svm/svm_ops.h
index 9430d6437c9f..36c8af87a707 100644
--- a/arch/x86/kvm/svm/svm_ops.h
+++ b/arch/x86/kvm/svm/svm_ops.h
@@ -61,9 +61,4 @@ static __always_inline void vmsave(unsigned long pa)
 	svm_asm1(vmsave, "a" (pa), "memory");
 }
 
-static __always_inline void vmload(unsigned long pa)
-{
-	svm_asm1(vmload, "a" (pa), "memory");
-}
-
 #endif /* __KVM_X86_SVM_OPS_H */
diff --git a/arch/x86/kvm/svm/vmenter.S b/arch/x86/kvm/svm/vmenter.S
index 5bc2ed7d79c0..0a4272faf80f 100644
--- a/arch/x86/kvm/svm/vmenter.S
+++ b/arch/x86/kvm/svm/vmenter.S
@@ -35,6 +35,7 @@
 /**
  * __svm_vcpu_run - Run a vCPU via a transition to SVM guest mode
  * @svm:	struct vcpu_svm *
+ * @hsave_pa:	unsigned long
  */
 SYM_FUNC_START(__svm_vcpu_run)
 	push %_ASM_BP
@@ -49,6 +50,9 @@ SYM_FUNC_START(__svm_vcpu_run)
 #endif
 	push %_ASM_BX
 
+	/* @hsave_pa is needed last after vmexit, save it first.  */
+	push %_ASM_ARG2
+
 	/* Save @svm. */
 	push %_ASM_ARG1
 
@@ -124,6 +128,11 @@ SYM_FUNC_START(__svm_vcpu_run)
 5:	vmsave %_ASM_AX
 6:
 
+	/* Pop @hsave_pa and restore GSBASE, allowing access to percpu data.  */
+	pop %_ASM_AX
+7:	vmload %_ASM_AX
+8:
+
 #ifdef CONFIG_RETPOLINE
 	/* IMPORTANT: Stuff the RSB immediately after VM-Exit, before RET! */
 	FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE
@@ -187,10 +196,14 @@ SYM_FUNC_START(__svm_vcpu_run)
 50:	cmpb $0, kvm_rebooting
 	jne 6b
 	ud2
+70:	cmpb $0, kvm_rebooting
+	jne 8b
+	ud2
 
 	_ASM_EXTABLE(1b, 10b)
 	_ASM_EXTABLE(3b, 30b)
 	_ASM_EXTABLE(5b, 50b)
+	_ASM_EXTABLE(7b, 70b)
 
 SYM_FUNC_END(__svm_vcpu_run)
 
-- 
2.31.1