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

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From: Sean Christopherson <seanjc@google.com>

commit 706a189dcf upstream.

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: Sean Christopherson <seanjc@google.com>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Nikolay Borisov <nik.borisov@suse.com>
Link: https://lore.kernel.org/all/20240213-delay-verw-v8-5-a6216d83edb7%40linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Pawan Gupta 2024-03-03 21:08:49 -08:00 committed by Greg Kroah-Hartman
parent 7a62647efc
commit ae46691220
2 changed files with 8 additions and 5 deletions
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7
arch/x86/kvm/vmx/run_flags.h
View file

@ -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 */

6
arch/x86/kvm/vmx/vmenter.S
View file

@ -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"