[PATCH 4.14 073/104] x86/kvm: Allow runtime control of L1D flush

From: Greg Kroah-Hartman
Date: Tue Aug 14 2018 - 13:37:12 EST


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

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

From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

commit 895ae47f9918833c3a880fbccd41e0692b37e7d9 upstream

All mitigation modes can be switched at run time with a static key now:

- Use sysfs_streq() instead of strcmp() to handle the trailing new line
from sysfs writes correctly.
- Make the static key management handle multiple invocations properly.
- Set the module parameter file to RW

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/20180713142322.954525119@xxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/cpu/bugs.c | 2 +-
arch/x86/kvm/vmx.c | 13 ++++++++-----
2 files changed, 9 insertions(+), 6 deletions(-)

--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -639,7 +639,7 @@ void x86_spec_ctrl_setup_ap(void)
#define pr_fmt(fmt) "L1TF: " fmt

#if IS_ENABLED(CONFIG_KVM_INTEL)
-enum vmx_l1d_flush_state l1tf_vmx_mitigation __ro_after_init = VMENTER_L1D_FLUSH_AUTO;
+enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_AUTO;
EXPORT_SYMBOL_GPL(l1tf_vmx_mitigation);
#endif

--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -237,12 +237,15 @@ static int vmx_setup_l1d_flush(enum vmx_

l1tf_vmx_mitigation = l1tf;

- if (l1tf == VMENTER_L1D_FLUSH_NEVER)
- return 0;
+ if (l1tf != VMENTER_L1D_FLUSH_NEVER)
+ static_branch_enable(&vmx_l1d_should_flush);
+ else
+ static_branch_disable(&vmx_l1d_should_flush);

- static_branch_enable(&vmx_l1d_should_flush);
if (l1tf == VMENTER_L1D_FLUSH_ALWAYS)
static_branch_enable(&vmx_l1d_flush_always);
+ else
+ static_branch_disable(&vmx_l1d_flush_always);
return 0;
}

@@ -252,7 +255,7 @@ static int vmentry_l1d_flush_parse(const

if (s) {
for (i = 0; i < ARRAY_SIZE(vmentry_l1d_param); i++) {
- if (!strcmp(s, vmentry_l1d_param[i].option))
+ if (sysfs_streq(s, vmentry_l1d_param[i].option))
return vmentry_l1d_param[i].cmd;
}
}
@@ -296,7 +299,7 @@ static const struct kernel_param_ops vme
.set = vmentry_l1d_flush_set,
.get = vmentry_l1d_flush_get,
};
-module_param_cb(vmentry_l1d_flush, &vmentry_l1d_flush_ops, NULL, S_IRUGO);
+module_param_cb(vmentry_l1d_flush, &vmentry_l1d_flush_ops, NULL, 0644);

#define NR_AUTOLOAD_MSRS 8