x86/kvm: Serialize L1D flush parameter setter

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@linutronix.de>
Tested-by: Jiri Kosina <jkosina@suse.cz>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/20180713142322.873642605@linutronix.de
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 332d92d..ad51ebb 100644 (file)
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -194,6 +194,7 @@ 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;
@@ -258,7 +259,7 @@ static int vmentry_l1d_flush_parse(const char *s)
 
 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;
@@ -278,7 +279,10 @@ static int vmentry_l1d_flush_set(const char *s, const struct kernel_param *kp)
                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)