[PATCH 01/13] KVM: monolithic: x86: remove kvm.ko

Andrea Arcangeli
2019-11-04T23:01:13Z

This is the first commit of a patch series that aims to replace the
modular kvm.ko kernel module with a monolithic kvm-intel/kvm-amd
model. This change has the only possible cons of wasting some disk
space in /lib/modules/. The pros are that it saves CPUS and some minor
iTLB and RAM which are more scarse resources than disk space.

The pointer to function virtual template model cannot provide any
runtime benefit because kvm-intel and kvm-amd can't be loaded at the
same time.

This removes kvm.ko and it links and duplicates all kvm.ko objects to
both kvm-amd and kvm-intel.

Linking both vmx and svm into the kernel at the same time isn't
possible anymore or the kvm_x86/kvm_x86_pmu external function names
would collide.

Explanation of Kbuild from Paolo Bonzini follows:

===
The left side of the "||" ensures that, if KVM=m, you can only choose
module build for both KVM_INTEL and KVM_AMD. Having just "depends on
KVM" would allow a pre-existing .config to choose the now-invalid
combination

CONFIG_KVM=y
CONFIG_KVM_INTEL=y
CONFIG_KVM_AMD=y

The right side of the "||" part is just for documentation, to avoid
that a selected symbol does not satisfy its dependencies.
====

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
---
arch/x86/kvm/Kconfig | 30 ++++++++++++++++++++++++++----
arch/x86/kvm/Makefile | 5 ++---
2 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index 840e12583b85..0d6e8809e359 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -59,9 +59,30 @@ config KVM

If unsure, say N.

+if KVM=y
+
+choice
+ prompt "KVM built-in support"
+ help
+ In order to build a kernel with support for both AMD and Intel
+ CPUs, you need to set CONFIG_KVM=m instead.
+
+config KVM_AMD_STATIC
+ select KVM_AMD
+ bool "AMD"
+
+config KVM_INTEL_STATIC
+ select KVM_INTEL
+ bool "Intel"
+
+endchoice
+
+endif
+
config KVM_INTEL
- tristate "KVM for Intel processors support"
- depends on KVM
+ tristate
+ prompt "KVM for Intel processors support" if KVM=m
+ depends on (KVM=m && m) || KVM_INTEL_STATIC
# for perf_guest_get_msrs():
depends on CPU_SUP_INTEL
---help---
@@ -72,8 +93,9 @@ config KVM_INTEL
will be called kvm-intel.

config KVM_AMD
- tristate "KVM for AMD processors support"
- depends on KVM
+ tristate
+ prompt "KVM for AMD processors support" if KVM=m
+ depends on (KVM=m && m) || KVM_AMD_STATIC
---help---
Provides support for KVM on AMD processors equipped with the AMD-V
(SVM) extensions.
diff --git a/arch/x86/kvm/Makefile b/arch/x86/kvm/Makefile
index 31ecf7a76d5a..68b81f381369 100644
--- a/arch/x86/kvm/Makefile
+++ b/arch/x86/kvm/Makefile
@@ -12,9 +12,8 @@ kvm-y += x86.o mmu.o emulate.o i8259.o irq.o lapic.o \
i8254.o ioapic.o irq_comm.o cpuid.o pmu.o mtrr.o \
hyperv.o page_track.o debugfs.o

-kvm-intel-y += vmx/vmx.o vmx/vmenter.o vmx/pmu_intel.o vmx/vmcs12.o vmx/evmcs.o vmx/nested.o
-kvm-amd-y += svm.o pmu_amd.o
+kvm-intel-y += vmx/vmx.o vmx/vmenter.o vmx/pmu_intel.o vmx/vmcs12.o vmx/evmcs.o vmx/nested.o $(kvm-y)
+kvm-amd-y += svm.o pmu_amd.o $(kvm-y)

-obj-$(CONFIG_KVM) += kvm.o
obj-$(CONFIG_KVM_INTEL) += kvm-intel.o
obj-$(CONFIG_KVM_AMD) += kvm-amd.o