[PATCH v7 003/102] KVM: Refactor CPU compatibility check on module initialiization

isaku.yamahata
2022-06-27T21:54:55Z

From: Isaku Yamahata <isaku.yamahata@intel.com>

Although non-x86 arch doesn't break as long as I inspected code, it's by
code inspection. This should be reviewed by each arch maintainers.

kvm_init() checks CPU compatibility by calling
kvm_arch_check_processor_compat() on all online CPUs. Move the callback
to hardware_enable_nolock() and add hardware_enable_all() and
hardware_disable_all().
Add arch specific callback kvm_arch_post_hardware_enable_setup() for arch
to do arch specific initialization that required hardware_enable_all().
This makes a room for TDX module to initialize on kvm module loading. TDX
module requires all online cpu to enable VMX by VMXON.

If kvm_arch_hardware_enable/disable() depend on (*) part, such dependency
must be called before kvm_init(). In fact kvm_intel() does. Although
other arch doesn't as long as I checked as follows, it should be reviewed
by each arch maintainers.

Before this patch:
- Arch module initialization
- kvm_init()
- kvm_arch_init()
- kvm_arch_check_processor_compat() on each CPUs
- post arch specific initialization ---- (*)

- when creating/deleting first/last VM
- kvm_arch_hardware_enable() on each CPUs --- (A)
- kvm_arch_hardware_disable() on each CPUs --- (B)

After this patch:
- Arch module initialization
- kvm_init()
- kvm_arch_init()
- kvm_arch_hardware_enable() on each CPUs (A)
- kvm_arch_check_processor_compat() on each CPUs
- kvm_arch_hardware_disable() on each CPUs (B)
- post arch specific initialization --- (*)

Code inspection result:
(A)/(B) can depend on (*) before this patch. If there is dependency, such
initialization must be moved before kvm_init() with this patch. VMX does
in fact. As long as I inspected other archs and find only mips has it.

- arch/mips/kvm/mips.c
module init function, kvm_mips_init(), does some initialization after
kvm_init(). Compile test only. Needs review.

- arch/x86/kvm/x86.c
- uses vm_list which is statically initialized.
- static_call(kvm_x86_hardware_enable)();
- SVM: (*) is empty.
- VMX: needs fix

- arch/powerpc/kvm/powerpc.c
kvm_arch_hardware_enable/disable() are nop

- arch/s390/kvm/kvm-s390.c
kvm_arch_hardware_enable/disable() are nop

- arch/arm64/kvm/arm.c
module init function, arm_init(), calls only kvm_init().
(*) is empty

- arch/riscv/kvm/main.c
module init function, riscv_kvm_init(), calls only kvm_init().
(*) is empty

Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
---
arch/mips/kvm/mips.c | 12 +++++++-----
arch/x86/kvm/vmx/vmx.c | 15 +++++++++++----
include/linux/kvm_host.h | 1 +
virt/kvm/kvm_main.c | 25 ++++++++++++++++++-------
4 files changed, 37 insertions(+), 16 deletions(-)

diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
index 092d09fb6a7e..17228584485d 100644
--- a/arch/mips/kvm/mips.c
+++ b/arch/mips/kvm/mips.c
@@ -1643,11 +1643,6 @@ static int __init kvm_mips_init(void)
}

ret = kvm_mips_entry_setup();
- if (ret)
- return ret;
-
- ret = kvm_init(NULL, sizeof(struct kvm_vcpu), 0, THIS_MODULE);
-
if (ret)
return ret;

@@ -1656,6 +1651,13 @@ static int __init kvm_mips_init(void)

register_die_notifier(&kvm_mips_csr_die_notifier);

+ ret = kvm_init(NULL, sizeof(struct kvm_vcpu), 0, THIS_MODULE);
+
+ if (ret) {
+ unregister_die_notifier(&kvm_mips_csr_die_notifier);
+ return ret;
+ }
+
return 0;
}

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 31e7630203fd..d3b68a6dec48 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -8372,6 +8372,15 @@ static void vmx_exit(void)
}
module_exit(vmx_exit);

+/* initialize before kvm_init() so that hardware_enable/disable() can work. */
+static void __init vmx_init_early(void)
+{
+ int cpu;
+
+ for_each_possible_cpu(cpu)
+ INIT_LIST_HEAD(&per_cpu(loaded_vmcss_on_cpu, cpu));
+}
+
static int __init vmx_init(void)
{
int r, cpu;
@@ -8409,6 +8418,7 @@ static int __init vmx_init(void)
}
#endif

+ vmx_init_early();
r = kvm_init(&vmx_init_ops, sizeof(struct vcpu_vmx),
__alignof__(struct vcpu_vmx), THIS_MODULE);
if (r)
@@ -8427,11 +8437,8 @@ static int __init vmx_init(void)
return r;
}

- for_each_possible_cpu(cpu) {
- INIT_LIST_HEAD(&per_cpu(loaded_vmcss_on_cpu, cpu));
-
+ for_each_possible_cpu(cpu)
pi_init_cpu(cpu);
- }

#ifdef CONFIG_KEXEC_CORE
rcu_assign_pointer(crash_vmclear_loaded_vmcss,
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index d4f130a9f5c8..79a4988fd51f 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1441,6 +1441,7 @@ void kvm_arch_create_vcpu_debugfs(struct kvm_vcpu *vcpu, struct dentry *debugfs_
int kvm_arch_hardware_enable(void);
void kvm_arch_hardware_disable(void);
int kvm_arch_hardware_setup(void *opaque);
+int kvm_arch_post_hardware_enable_setup(void *opaque);
void kvm_arch_hardware_unsetup(void);
int kvm_arch_check_processor_compat(void);
int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index a5bada53f1fe..cee799265ce6 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -4899,8 +4899,13 @@ static void hardware_enable_nolock(void *junk)

cpumask_set_cpu(cpu, cpus_hardware_enabled);

+ r = kvm_arch_check_processor_compat();
+ if (r)
+ goto out;
+
r = kvm_arch_hardware_enable();

+out:
if (r) {
cpumask_clear_cpu(cpu, cpus_hardware_enabled);
atomic_inc(&hardware_enable_failed);
@@ -5697,9 +5702,9 @@ void kvm_unregister_perf_callbacks(void)
}
#endif

-static void check_processor_compat(void *rtn)
+__weak int kvm_arch_post_hardware_enable_setup(void *opaque)
{
- *(int *)rtn = kvm_arch_check_processor_compat();
+ return 0;
}

int kvm_init(void *opaque, unsigned vcpu_size, unsigned vcpu_align,
@@ -5732,11 +5737,17 @@ int kvm_init(void *opaque, unsigned vcpu_size, unsigned vcpu_align,
if (r < 0)
goto out_free_1;

- for_each_online_cpu(cpu) {
- smp_call_function_single(cpu, check_processor_compat, &r, 1);
- if (r < 0)
- goto out_free_2;
- }
+ /* hardware_enable_nolock() checks CPU compatibility on each CPUs. */
+ r = hardware_enable_all();
+ if (r)
+ goto out_free_2;
+ /*
+ * Arch specific initialization that requires to enable virtualization
+ * feature. e.g. TDX module initialization requires VMXON on all
+ * present CPUs.
+ */
+ kvm_arch_post_hardware_enable_setup(opaque);
+ hardware_disable_all();

r = cpuhp_setup_state_nocalls(CPUHP_AP_KVM_STARTING, "kvm/cpu:starting",
kvm_starting_cpu, kvm_dying_cpu);
--
2.25.1