On 7/5/20 2:22 PM, Abhishek Bhardwaj wrote:
On Sun, Jul 5, 2020 at 8:57 AM Waiman Long <longman@xxxxxxxxxx> wrote:
On 7/5/20 11:23 AM, Mike Rapoport wrote:
Nothing prevents people from continuing to use the command line
options if they want, right? This just allows a different default.
So if a distro is security focused and decided that it wanted a slower
/ more secure default then it could ship that way but individual users
could still override, right?
Well, nothing prevents you from continuing to use the command line as
well;-)
I can see why whould you want an ability to select compile time default
for an option, but I'm really not thrilled by the added ifdefery.
It turns out that CONFIG_KVM_VMENTRY_L1D_FLUSH values match the enum
vmx_l1d_flush_state values. So one way to reduce the ifdefery is to do,
for example,
+#ifdef CONFIG_KVM_VMENTRY_L1D_FLUSH
+#define VMENTER_L1D_FLUSH_DEFAULT CONFIG_KVM_VMENTRY_L1D_FLUSH
+#else
+#define VMENTER_L1D_FLUSH_DEFAULT VMENTER_L1D_FLUSH_AUTO
#endif
-enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_AUTO;
+enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_DEFAULT;
Of course, we may need to add a comment on enum vmx_l1d_flush_state
definition to highlight the dependency of CONFIG_KVM_VMENTRY_L1D_FLUSH
on it to avoid future mismatch.
I explicitly wanted to avoid doing that for this very reason. In my
opinion this is brittle and bound to be missed
sooner or later.
That is why I said a comment will have to be added to highlight this
dependency. For instance,
+/*
+ * Three of the enums are explicitly assigned as the KVM_VMENTRY_L1D_FLUSH
+ * config entry in arch/x86/kvm/Kconfig depends on these values.
+ */
enum vmx_l1d_flush_state {
VMENTER_L1D_FLUSH_AUTO,
- VMENTER_L1D_FLUSH_NEVER,
- VMENTER_L1D_FLUSH_COND,
- VMENTER_L1D_FLUSH_ALWAYS,
+ VMENTER_L1D_FLUSH_NEVER = 1,
+ VMENTER_L1D_FLUSH_COND = 2,
+ VMENTER_L1D_FLUSH_ALWAYS = 3,
VMENTER_L1D_FLUSH_EPT_DISABLED,
VMENTER_L1D_FLUSH_NOT_REQUIRED,
};
Of course, this is just a suggestion.
Cheers,
Longman
