Commit 706a189d authored by Sean Christopherson's avatar Sean Christopherson Committed by Dave Hansen
Browse files

KVM/VMX: Use BT+JNC, i.e. EFLAGS.CF to select VMRESUME vs. VMLAUNCH 



Use EFLAGS.CF instead of EFLAGS.ZF to track whether to use VMRESUME versus
VMLAUNCH.  Freeing up EFLAGS.ZF will allow doing VERW, which clobbers ZF,
for MDS mitigations as late as possible without needing to duplicate VERW
for both paths.

Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Signed-off-by: default avatarPawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: default avatarNikolay Borisov <nik.borisov@suse.com>
Link: https://lore.kernel.org/all/20240213-delay-verw-v8-5-a6216d83edb7%40linux.intel.com
parent 6613d82e

arch/x86/kvm/vmx/run_flags.h

+5 −2
Original line number Diff line number Diff line
@@ -2,7 +2,10 @@ 
#ifndef __KVM_X86_VMX_RUN_FLAGS_H

#define __KVM_X86_VMX_RUN_FLAGS_H



#define VMX_RUN_VMRESUME	(1 << 0)

#define VMX_RUN_SAVE_SPEC_CTRL	(1 << 1)

#define VMX_RUN_VMRESUME_SHIFT		0

#define VMX_RUN_SAVE_SPEC_CTRL_SHIFT	1



#define VMX_RUN_VMRESUME		BIT(VMX_RUN_VMRESUME_SHIFT)

#define VMX_RUN_SAVE_SPEC_CTRL		BIT(VMX_RUN_SAVE_SPEC_CTRL_SHIFT)



#endif /* __KVM_X86_VMX_RUN_FLAGS_H */

arch/x86/kvm/vmx/vmenter.S

+3 −3
Original line number Diff line number Diff line
@@ -139,7 +139,7 @@ SYM_FUNC_START(__vmx_vcpu_run) 
	mov (%_ASM_SP), %_ASM_AX



	/* Check if vmlaunch or vmresume is needed */

	test $VMX_RUN_VMRESUME, %ebx

	bt   $VMX_RUN_VMRESUME_SHIFT, %ebx



	/* Load guest registers.  Don't clobber flags. */

	mov VCPU_RCX(%_ASM_AX), %_ASM_CX
@@ -161,8 +161,8 @@ SYM_FUNC_START(__vmx_vcpu_run) 
	/* Load guest RAX.  This kills the @regs pointer! */

	mov VCPU_RAX(%_ASM_AX), %_ASM_AX



	/* Check EFLAGS.ZF from 'test VMX_RUN_VMRESUME' above */

	jz .Lvmlaunch

	/* Check EFLAGS.CF from the VMX_RUN_VMRESUME bit test above. */

	jnc .Lvmlaunch



	/*

	 * After a successful VMRESUME/VMLAUNCH, control flow "magically"