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: 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

diff --git a/arch/x86/kvm/vmx/run_flags.h b/arch/x86/kvm/vmx/run_flags.h
index edc3f16cc1896f29e4eef46da685d22b4c31c668..6a9bfdfbb6e59b2e613385cd2ad46cc651a0eb28 100644 (file)
--- a/arch/x86/kvm/vmx/run_flags.h
+++ b/arch/x86/kvm/vmx/run_flags.h
@@ -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 */

diff --git a/arch/x86/kvm/vmx/vmenter.S b/arch/x86/kvm/vmx/vmenter.S
index 906ecd001511355d0939e4e90a3994a7bd9809e3..ef7cfbad4d5732cce3717b7134bfe12c0cfac7b7 100644 (file)
--- a/arch/x86/kvm/vmx/vmenter.S
+++ b/arch/x86/kvm/vmx/vmenter.S
@@ -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"