This change adds a new kernel configuration that sets the l1d cache
flush setting at compile time rather than at run time.
The reasons for this change are as follows -
- Kernel command line arguments are getting unwieldy. These parameters
are not a scalable way to set the kernel config. They're intended as a
super limited way for the bootloader to pass info to the kernel and
also as a way for end users who are not compiling the kernel themselves
to tweak the kernel behavior.
- Also, if a user wants this setting from the start. It's a definite
smell that it deserves to be a compile time thing rather than adding
extra code plus whatever miniscule time at runtime to pass an
extra argument.
- Finally, it doesn't preclude the runtime / kernel command line way.
Users are free to use those as well.
Signed-off-by: Abhishek Bhardwaj <abhishe...@google.com>
---
Changes in v5:
- Fix indentation of the help text in the KConfig.
Changes in v4:
- Add motivation for the change in the commit message.
Changes in v3:
- Change depends on to only x86_64.
- Remove copy paste errors at the end of the KConfig.
Changes in v2:
- Fix typo in the help of the new KConfig.
arch/x86/kernel/cpu/bugs.c | 8 ++++++++
arch/x86/kvm/Kconfig | 13 +++++++++++++
2 files changed, 21 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..cb2639dfb6da1 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -107,4 +107,17 @@ 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_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 - Conditionally flush.
+ 3 - Always flush.
+
endif # VIRTUALIZATION
--
2.27.0.383.g050319c2ae-goog
