Messages in this thread | | | Subject | Re: [PATCH v3] x86/speculation/l1tf: Add KConfig for setting the L1D cache flush mode | From | Waiman Long <> | Date | Sun, 5 Jul 2020 14:48:01 -0400 |
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On 7/5/20 2:22 PM, Abhishek Bhardwaj wrote: > On Sun, Jul 5, 2020 at 8:57 AM Waiman Long <longman@redhat.com> 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
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