Date:   Tue, 19 Jul 2022 21:13:28 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Josh Poimboeuf <jpoimboe@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...e.de>, Sasha Levin <sashal@...nel.org>,
        seanjc@...gle.com, pbonzini@...hat.com, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        x86@...nel.org, kvm@...r.kernel.org
Subject: [PATCH AUTOSEL 5.15 20/42] KVM: VMX: Flatten __vmx_vcpu_run()

From: Josh Poimboeuf <jpoimboe@...nel.org>

[ Upstream commit 8bd200d23ec42d66ccd517a72dd0b9cc6132d2fd ]

Move the vmx_vm{enter,exit}() functionality into __vmx_vcpu_run().  This
will make it easier to do the spec_ctrl handling before the first RET.

Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Borislav Petkov <bp@...e.de>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/x86/kvm/vmx/vmenter.S | 119 ++++++++++++++-----------------------
 1 file changed, 46 insertions(+), 73 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmenter.S b/arch/x86/kvm/vmx/vmenter.S
index 435c187927c4..c83163fb2e9c 100644
--- a/arch/x86/kvm/vmx/vmenter.S
+++ b/arch/x86/kvm/vmx/vmenter.S
@@ -30,68 +30,6 @@
 
 .section .noinstr.text, "ax"
 
-/**
- * vmx_vmenter - VM-Enter the current loaded VMCS
- *
- * %RFLAGS.ZF:	!VMCS.LAUNCHED, i.e. controls VMLAUNCH vs. VMRESUME
- *
- * Returns:
- *	%RFLAGS.CF is set on VM-Fail Invalid
- *	%RFLAGS.ZF is set on VM-Fail Valid
- *	%RFLAGS.{CF,ZF} are cleared on VM-Success, i.e. VM-Exit
- *
- * Note that VMRESUME/VMLAUNCH fall-through and return directly if
- * they VM-Fail, whereas a successful VM-Enter + VM-Exit will jump
- * to vmx_vmexit.
- */
-SYM_FUNC_START_LOCAL(vmx_vmenter)
-	/* EFLAGS.ZF is set if VMCS.LAUNCHED == 0 */
-	je 2f
-
-1:	vmresume
-	RET
-
-2:	vmlaunch
-	RET
-
-3:	cmpb $0, kvm_rebooting
-	je 4f
-	RET
-4:	ud2
-
-	_ASM_EXTABLE(1b, 3b)
-	_ASM_EXTABLE(2b, 3b)
-
-SYM_FUNC_END(vmx_vmenter)
-
-/**
- * vmx_vmexit - Handle a VMX VM-Exit
- *
- * Returns:
- *	%RFLAGS.{CF,ZF} are cleared on VM-Success, i.e. VM-Exit
- *
- * This is vmx_vmenter's partner in crime.  On a VM-Exit, control will jump
- * here after hardware loads the host's state, i.e. this is the destination
- * referred to by VMCS.HOST_RIP.
- */
-SYM_FUNC_START(vmx_vmexit)
-#ifdef CONFIG_RETPOLINE
-	ALTERNATIVE "jmp .Lvmexit_skip_rsb", "", X86_FEATURE_RETPOLINE
-	/* Preserve guest's RAX, it's used to stuff the RSB. */
-	push %_ASM_AX
-
-	/* IMPORTANT: Stuff the RSB immediately after VM-Exit, before RET! */
-	FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE
-
-	/* Clear RFLAGS.CF and RFLAGS.ZF to preserve VM-Exit, i.e. !VM-Fail. */
-	or $1, %_ASM_AX
-
-	pop %_ASM_AX
-.Lvmexit_skip_rsb:
-#endif
-	RET
-SYM_FUNC_END(vmx_vmexit)
-
 /**
  * __vmx_vcpu_run - Run a vCPU via a transition to VMX guest mode
  * @vmx:	struct vcpu_vmx * (forwarded to vmx_update_host_rsp)
@@ -124,8 +62,7 @@ SYM_FUNC_START(__vmx_vcpu_run)
 	/* Copy @launched to BL, _ASM_ARG3 is volatile. */
 	mov %_ASM_ARG3B, %bl
 
-	/* Adjust RSP to account for the CALL to vmx_vmenter(). */
-	lea -WORD_SIZE(%_ASM_SP), %_ASM_ARG2
+	lea (%_ASM_SP), %_ASM_ARG2
 	call vmx_update_host_rsp
 
 	/* Load @regs to RAX. */
@@ -154,11 +91,37 @@ SYM_FUNC_START(__vmx_vcpu_run)
 	/* Load guest RAX.  This kills the @regs pointer! */
 	mov VCPU_RAX(%_ASM_AX), %_ASM_AX
 
-	/* Enter guest mode */
-	call vmx_vmenter
+	/* Check EFLAGS.ZF from 'testb' above */
+	je .Lvmlaunch
+
+	/*
+	 * After a successful VMRESUME/VMLAUNCH, control flow "magically"
+	 * resumes below at 'vmx_vmexit' due to the VMCS HOST_RIP setting.
+	 * So this isn't a typical function and objtool needs to be told to
+	 * save the unwind state here and restore it below.
+	 */
+	UNWIND_HINT_SAVE
+
+/*
+ * If VMRESUME/VMLAUNCH and corresponding vmexit succeed, execution resumes at
+ * the 'vmx_vmexit' label below.
+ */
+.Lvmresume:
+	vmresume
+	jmp .Lvmfail
+
+.Lvmlaunch:
+	vmlaunch
+	jmp .Lvmfail
+
+	_ASM_EXTABLE(.Lvmresume, .Lfixup)
+	_ASM_EXTABLE(.Lvmlaunch, .Lfixup)
 
-	/* Jump on VM-Fail. */
-	jbe 2f
+SYM_INNER_LABEL(vmx_vmexit, SYM_L_GLOBAL)
+
+	/* Restore unwind state from before the VMRESUME/VMLAUNCH. */
+	UNWIND_HINT_RESTORE
+	ENDBR
 
 	/* Temporarily save guest's RAX. */
 	push %_ASM_AX
@@ -185,9 +148,13 @@ SYM_FUNC_START(__vmx_vcpu_run)
 	mov %r15, VCPU_R15(%_ASM_AX)
 #endif
 
+	/* IMPORTANT: RSB must be stuffed before the first return. */
+	FILL_RETURN_BUFFER %_ASM_BX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE
+
 	/* Clear RAX to indicate VM-Exit (as opposed to VM-Fail). */
 	xor %eax, %eax
 
+.Lclear_regs:
 	/*
 	 * Clear all general purpose registers except RSP and RAX to prevent
 	 * speculative use of the guest's values, even those that are reloaded
@@ -197,7 +164,7 @@ SYM_FUNC_START(__vmx_vcpu_run)
 	 * free.  RSP and RAX are exempt as RSP is restored by hardware during
 	 * VM-Exit and RAX is explicitly loaded with 0 or 1 to return VM-Fail.
 	 */
-1:	xor %ecx, %ecx
+	xor %ecx, %ecx
 	xor %edx, %edx
 	xor %ebx, %ebx
 	xor %ebp, %ebp
@@ -216,8 +183,8 @@ SYM_FUNC_START(__vmx_vcpu_run)
 
 	/* "POP" @regs. */
 	add $WORD_SIZE, %_ASM_SP
-	pop %_ASM_BX
 
+	pop %_ASM_BX
 #ifdef CONFIG_X86_64
 	pop %r12
 	pop %r13
@@ -230,9 +197,15 @@ SYM_FUNC_START(__vmx_vcpu_run)
 	pop %_ASM_BP
 	RET
 
-	/* VM-Fail.  Out-of-line to avoid a taken Jcc after VM-Exit. */
-2:	mov $1, %eax
-	jmp 1b
+.Lfixup:
+	cmpb $0, kvm_rebooting
+	jne .Lvmfail
+	ud2
+.Lvmfail:
+	/* VM-Fail: set return value to 1 */
+	mov $1, %eax
+	jmp .Lclear_regs
+
 SYM_FUNC_END(__vmx_vcpu_run)
 
 
-- 
2.35.1

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