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

From: Sean Christopherson <seanjc@google.com>

commit 706a189dcf74d3b3f955e9384785e726ed6c7c80 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>

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 be275a0410a89957e79ffe57747e50ed36876e2f..b3b13ec04bac144e7b31b0b604af7bac04e05545 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"