[PATCH 4/8] KVM: SVM: move guest vmsave/vmload to assembly

[Paolo Bonzini <pbonzini@redhat.com>]

FILL_RETURN_BUFFER can access percpu data, therefore vmload of the
host save area must be executed first.  First of all, move the
VMCB vmsave/vmload to assembly.

The idea on how to number the exception tables is stolen from
a prototype patch by Peter Zijlstra.

Cc: stable@vger.kernel.org
Fixes: f14eec0a3203 ("KVM: SVM: move more vmentry code to assembly")
Link: <https://lore.kernel.org/all/f571e404-e625-bae1-10e9-449b2eb4cbd8@citrix.com/>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kernel/asm-offsets.c |  2 ++
 arch/x86/kvm/svm/svm.c        |  9 -------
 arch/x86/kvm/svm/vmenter.S    | 50 +++++++++++++++++++++++++++--------
 3 files changed, 41 insertions(+), 20 deletions(-)

diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c
index 85de7e4fe59a..f01293a1e594 100644
--- a/arch/x86/kernel/asm-offsets.c
+++ b/arch/x86/kernel/asm-offsets.c
@@ -113,6 +113,8 @@ static void __used common(void)
 	if (IS_ENABLED(CONFIG_KVM_AMD)) {
 		BLANK();
 		OFFSET(SVM_vcpu_arch_regs, vcpu_svm, vcpu.arch.regs);
+		OFFSET(SVM_vmcb01, vcpu_svm, vmcb01);
+		OFFSET(KVM_VMCB_pa, kvm_vmcb_info, pa);
 	}
 
 	if (IS_ENABLED(CONFIG_KVM_INTEL)) {
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 4cfa62e66a0e..ae65cdcab660 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3924,16 +3924,7 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu)
 	} else {
 		struct svm_cpu_data *sd = per_cpu(svm_data, vcpu->cpu);
 
-		/*
-		 * Use a single vmcb (vmcb01 because it's always valid) for
-		 * context switching guest state via VMLOAD/VMSAVE, that way
-		 * the state doesn't need to be copied between vmcb01 and
-		 * vmcb02 when switching vmcbs for nested virtualization.
-		 */
-		vmload(svm->vmcb01.pa);
 		__svm_vcpu_run(vmcb_pa, svm);
-		vmsave(svm->vmcb01.pa);
-
 		vmload(__sme_page_pa(sd->save_area));
 	}
 
diff --git a/arch/x86/kvm/svm/vmenter.S b/arch/x86/kvm/svm/vmenter.S
index dc558d0a589e..4709bc8868d7 100644
--- a/arch/x86/kvm/svm/vmenter.S
+++ b/arch/x86/kvm/svm/vmenter.S
@@ -1,6 +1,7 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 #include <linux/linkage.h>
 #include <asm/asm.h>
+#include <asm/asm-offsets.h>
 #include <asm/bitsperlong.h>
 #include <asm/kvm_vcpu_regs.h>
 #include <asm/nospec-branch.h>
@@ -27,6 +28,8 @@
 #define VCPU_R15	(SVM_vcpu_arch_regs + __VCPU_REGS_R15 * WORD_SIZE)
 #endif
 
+#define SVM_vmcb01_pa	(SVM_vmcb01 + KVM_VMCB_pa)
+
 .section .noinstr.text, "ax"
 
 /**
@@ -56,6 +59,16 @@ SYM_FUNC_START(__svm_vcpu_run)
 	/* Move @svm to RDI. */
 	mov %_ASM_ARG2, %_ASM_DI
 
+	/*
+	 * Use a single vmcb (vmcb01 because it's always valid) for
+	 * context switching guest state via VMLOAD/VMSAVE, that way
+	 * the state doesn't need to be copied between vmcb01 and
+	 * vmcb02 when switching vmcbs for nested virtualization.
+	 */
+	mov SVM_vmcb01_pa(%_ASM_DI), %_ASM_AX
+1:	vmload %_ASM_AX
+2:
+
 	/* "POP" @vmcb to RAX. */
 	pop %_ASM_AX
 
@@ -80,16 +93,11 @@ SYM_FUNC_START(__svm_vcpu_run)
 	/* Enter guest mode */
 	sti
 
-1:	vmrun %_ASM_AX
-
-2:	cli
-
-#ifdef CONFIG_RETPOLINE
-	/* IMPORTANT: Stuff the RSB immediately after VM-Exit, before RET! */
-	FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE
-#endif
+3:	vmrun %_ASM_AX
+4:
+	cli
 
-	/* "POP" @svm to RAX. */
+	/* Pop @svm to RAX while it's the only available register. */
 	pop %_ASM_AX
 
 	/* Save all guest registers.  */
@@ -110,6 +118,18 @@ SYM_FUNC_START(__svm_vcpu_run)
 	mov %r15, VCPU_R15(%_ASM_AX)
 #endif
 
+	/* @svm can stay in RDI from now on.  */
+	mov %_ASM_AX, %_ASM_DI
+
+	mov SVM_vmcb01_pa(%_ASM_DI), %_ASM_AX
+5:	vmsave %_ASM_AX
+6:
+
+#ifdef CONFIG_RETPOLINE
+	/* IMPORTANT: Stuff the RSB immediately after VM-Exit, before RET! */
+	FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE
+#endif
+
 	/*
 	 * Mitigate RETBleed for AMD/Hygon Zen uarch. RET should be
 	 * untrained as soon as we exit the VM and are back to the
@@ -159,11 +179,19 @@ SYM_FUNC_START(__svm_vcpu_run)
 	pop %_ASM_BP
 	RET
 
-3:	cmpb $0, kvm_rebooting
+10:	cmpb $0, kvm_rebooting
 	jne 2b
 	ud2
+30:	cmpb $0, kvm_rebooting
+	jne 4b
+	ud2
+50:	cmpb $0, kvm_rebooting
+	jne 6b
+	ud2
 
-	_ASM_EXTABLE(1b, 3b)
+	_ASM_EXTABLE(1b, 10b)
+	_ASM_EXTABLE(3b, 30b)
+	_ASM_EXTABLE(5b, 50b)
 
 SYM_FUNC_END(__svm_vcpu_run)
 
-- 
2.31.1