[PATCH 4.17 68/97] x86/kvm: Serialize L1D flush parameter setter

[Greg Kroah-Hartman]

4.17-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

commit dd4bfa739a72508b75760b393d129ed7b431daab upstream

Writes to the parameter files are not serialized at the sysfs core
level, so local serialization is required.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Tested-by: Jiri Kosina <jkosina@xxxxxxx>
Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Reviewed-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20180713142322.873642605@xxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/x86/kvm/vmx.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -193,6 +193,7 @@ extern const ulong vmx_return;
 
 static DEFINE_STATIC_KEY_FALSE(vmx_l1d_should_flush);
 static DEFINE_STATIC_KEY_FALSE(vmx_l1d_flush_always);
+static DEFINE_MUTEX(vmx_l1d_flush_mutex);
 
 /* Storage for pre module init parameter parsing */
 static enum vmx_l1d_flush_state __read_mostly vmentry_l1d_flush_param = VMENTER_L1D_FLUSH_AUTO;
@@ -257,7 +258,7 @@ static int vmentry_l1d_flush_parse(const
 
 static int vmentry_l1d_flush_set(const char *s, const struct kernel_param *kp)
 {
-	int l1tf;
+	int l1tf, ret;
 
 	if (!boot_cpu_has(X86_BUG_L1TF))
 		return 0;
@@ -277,7 +278,10 @@ static int vmentry_l1d_flush_set(const c
 		return 0;
 	}
 
-	return vmx_setup_l1d_flush(l1tf);
+	mutex_lock(&vmx_l1d_flush_mutex);
+	ret = vmx_setup_l1d_flush(l1tf);
+	mutex_unlock(&vmx_l1d_flush_mutex);
+	return ret;
 }
 
 static int vmentry_l1d_flush_get(char *s, const struct kernel_param *kp)