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

Abhishek Bhardwaj
2020-07-02T16:19:24Z

This change adds a new kernel configuration that sets the l1d cache
flush setting at compile time rather than at run time.

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