This is a note to let you know that I've just added the patch titled
KVM/VMX: Use BT+JNC, i.e. EFLAGS.CF to select VMRESUME vs. VMLAUNCH
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
kvm-vmx-use-bt-jnc-i.e.-eflags.cf-to-select-vmresume-vs.-vmlaunch.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From stable+bounces-25812-greg=kroah.com@xxxxxxxxxxxxxxx Mon Mar 4 06:08:54 2024
From: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>
Date: Sun, 3 Mar 2024 21:08:49 -0800
Subject: KVM/VMX: Use BT+JNC, i.e. EFLAGS.CF to select VMRESUME vs. VMLAUNCH
To: stable@xxxxxxxxxxxxxxx
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>, Sean Christopherson <seanjc@xxxxxxxxxx>, Nikolay Borisov <nik.borisov@xxxxxxxx>
Message-ID: <20240303-delay-verw-backport-6-6-y-v2-4-40ce56b521a5@xxxxxxxxxxxxxxx>
Content-Disposition: inline
From: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>
From: Sean Christopherson <seanjc@xxxxxxxxxx>
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@xxxxxxxxxx>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Reviewed-by: Nikolay Borisov <nik.borisov@xxxxxxxx>
Link: https://lore.kernel.org/all/20240213-delay-verw-v8-5-a6216d83edb7%40linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kvm/vmx/run_flags.h | 7 +++++--
arch/x86/kvm/vmx/vmenter.S | 6 +++---
2 files changed, 8 insertions(+), 5 deletions(-)
--- 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 */
--- 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"
Patches currently in stable-queue which might be from kroah.com@xxxxxxxxxxxxxxx are
queue-6.6/x86-bugs-use-alternative-instead-of-mds_user_clear-static-key.patch
queue-6.6/kvm-vmx-move-verw-closer-to-vmentry-for-mds-mitigation.patch
queue-6.6/x86-entry_32-add-verw-just-before-userspace-transition.patch
queue-6.6/x86-entry_64-add-verw-just-before-userspace-transition.patch
queue-6.6/kvm-vmx-use-bt-jnc-i.e.-eflags.cf-to-select-vmresume-vs.-vmlaunch.patch
