Re: [PATCH] x86/speculation/l1tf: Add KConfig for setting the L1D cache flush mode

mark gross
2020-07-06T15:01:49Z

On Thu, Jul 02, 2020 at 09:19:16AM -0700, Abhishek Bhardwaj wrote:
> This change adds a new kernel configuration that sets the l1d cache
> flush setting at compile time rather than at run time.

Why is this desired?

--mark

>
> Signed-off-by: Abhishek Bhardwaj <abhishekbh@google.com>
> ---
>
> arch/x86/kernel/cpu/bugs.c | 8 ++++++++
> arch/x86/kvm/Kconfig | 17 +++++++++++++++++
> 2 files changed, 25 insertions(+)
>
> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
> index 0b71970d2d3d2..1dcc875cf5547 100644
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -1406,7 +1406,15 @@ enum l1tf_mitigations l1tf_mitigation __ro_after_init = L1TF_MITIGATION_FLUSH;
> #if IS_ENABLED(CONFIG_KVM_INTEL)
> EXPORT_SYMBOL_GPL(l1tf_mitigation);
> #endif
> +#if (CONFIG_KVM_VMENTRY_L1D_FLUSH == 1)
> +enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_NEVER;
> +#elif (CONFIG_KVM_VMENTRY_L1D_FLUSH == 2)
> +enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_COND;
> +#elif (CONFIG_KVM_VMENTRY_L1D_FLUSH == 3)
> +enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_ALWAYS;
> +#else
> enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_AUTO;
> +#endif
> EXPORT_SYMBOL_GPL(l1tf_vmx_mitigation);
>
> /*
> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> index b277a2db62676..f82a0c564e931 100644
> --- a/arch/x86/kvm/Kconfig
> +++ b/arch/x86/kvm/Kconfig
> @@ -107,4 +107,21 @@ config KVM_MMU_AUDIT
> This option adds a R/W kVM module parameter 'mmu_audit', which allows
> auditing of KVM MMU events at runtime.
>
> +config KVM_VMENTRY_L1D_FLUSH
> + int "L1D cache flush settings (1-3)"
> + range 1 3
> + default "2"
> + depends on KVM && X86 && X86_64
> + help
> + This setting determines the L1D cache flush behavior before a VMENTER.
> + This is similar to setting the option / parameter to
> + kvm-intel.vmentry_l1d_flush.
> + 1 - Never flush.
> + 2 - Conditinally flush.
> + 3 - Always flush.
> +
> +# OK, it's a little counter-intuitive to do this, but it puts it neatly under
> +# the virtualization menu.
> +source "drivers/vhost/Kconfig"
> +
> endif # VIRTUALIZATION
> --
> 2.27.0.212.ge8ba1cc988-goog
>