Register KVM's cpuhp and syscore callbacks when enabling virtualization in
hardware, as the sole purpose of said callbacks is to disable and re-enable
virtualization as needed.
The primary motivation for this series is to simplify dealing with enabling
virtualization for Intel's TDX, which needs to enable virtualization
when kvm-intel.ko is loaded, i.e. long before the first VM is created. TDX
doesn't _need_ to keep virtualization enabled, but doing so is much simpler
for KVM (see patch 3).
That said, this is a nice cleanup on its own, assuming I haven't broken
something. By registering the callbacks on-demand, the callbacks themselves
don't need to check kvm_usage_count, because their very existence implies a
non-zero count.
The meat is in patch 1. Patches 2 renames the helpers so that patch 3 is
less awkward. Patch 3 adds a module param to enable virtualization when KVM
is loaded. Patches 4-6 are tangentially related x86 cleanups to registers
KVM's "emergency disable" callback on-demand, same as the syscore callbacks.
The suspend/resume and cphup paths still need to be fully tested, as do
non-x86 architectures.
v3:
- Collect reviews/acks.
- Switch to kvm_usage_lock in a dedicated patch, Cc'd for stable@. [Chao]
- Enable virt at load by default. [Chao]
- Add comments to document how kvm_arch_{en,dis}able_virtualization() fit
into the overall flow. [Kai]
v2:
- https://lore.kernel.org/all/[email protected]
- Use a dedicated mutex to avoid lock inversion issues between kvm_lock and
the cpuhp lock.
- Register emergency disable callbacks on-demand. [Kai]
- Drop an unintended s/junk/ign rename. [Kai]
- Decrement kvm_usage_count on failure. [Chao]
v1: https://lore.kernel.org/all/[email protected]
Sean Christopherson (8):
KVM: Use dedicated mutex to protect kvm_usage_count to avoid deadlock
KVM: Register cpuhp and syscore callbacks when enabling hardware
KVM: Rename functions related to enabling virtualization hardware
KVM: Add a module param to allow enabling virtualization when KVM is
loaded
KVM: Add arch hooks for enabling/disabling virtualization
x86/reboot: Unconditionally define cpu_emergency_virt_cb typedef
KVM: x86: Register "emergency disable" callbacks when virt is enabled
KVM: Enable virtualization at load/initialization by default
Documentation/virt/kvm/locking.rst | 19 ++-
arch/x86/include/asm/kvm_host.h | 3 +
arch/x86/include/asm/reboot.h | 2 +-
arch/x86/kvm/svm/svm.c | 5 +-
arch/x86/kvm/vmx/main.c | 2 +
arch/x86/kvm/vmx/vmx.c | 6 +-
arch/x86/kvm/vmx/x86_ops.h | 1 +
arch/x86/kvm/x86.c | 10 ++
include/linux/kvm_host.h | 14 ++
virt/kvm/kvm_main.c | 258 ++++++++++++++---------------
10 files changed, 175 insertions(+), 145 deletions(-)
base-commit: af0903ab52ee6d6f0f63af67fa73d5eb00f79b9a
--
2.45.2.505.gda0bf45e8d-goog
Rename the various functions that enable virtualization to prepare for
upcoming changes, and to clean up artifacts of KVM's previous behavior,
which required manually juggling locks around kvm_usage_count.
Drop the "nolock" qualifier from per-CPU functions now that there are no
"nolock" implementations of the "all" variants, i.e. now that calling a
non-nolock function from a nolock function isn't confusing (unlike this
sentence).
Drop "all" from the outer helpers as they no longer manually iterate
over all CPUs, and because it might not be obvious what "all" refers to.
Instead, use double-underscores to communicate that the per-CPU functions
are helpers to the outer APIs.
Opportunistically prepend "kvm" to all functions to help make it clear
that they are KVM helpers, but mostly there's no reason not to.
Lastly, use "virtualization" instead of "hardware", because while the
functions do enable virtualization in hardware, there are a _lot_ of
things that KVM enables in hardware.
Reviewed-by: Chao Gao <[email protected]>
Reviewed-by: Kai Huang <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
---
virt/kvm/kvm_main.c | 32 ++++++++++++++++----------------
1 file changed, 16 insertions(+), 16 deletions(-)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index f6b114f42433..98e52d12f137 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -138,8 +138,8 @@ static int kvm_no_compat_open(struct inode *inode, struct file *file)
#define KVM_COMPAT(c) .compat_ioctl = kvm_no_compat_ioctl, \
.open = kvm_no_compat_open
#endif
-static int hardware_enable_all(void);
-static void hardware_disable_all(void);
+static int kvm_enable_virtualization(void);
+static void kvm_disable_virtualization(void);
static void kvm_io_bus_destroy(struct kvm_io_bus *bus);
@@ -1215,7 +1215,7 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
if (r)
goto out_err_no_arch_destroy_vm;
- r = hardware_enable_all();
+ r = kvm_enable_virtualization();
if (r)
goto out_err_no_disable;
@@ -1258,7 +1258,7 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
mmu_notifier_unregister(&kvm->mmu_notifier, current->mm);
#endif
out_err_no_mmu_notifier:
- hardware_disable_all();
+ kvm_disable_virtualization();
out_err_no_disable:
kvm_arch_destroy_vm(kvm);
out_err_no_arch_destroy_vm:
@@ -1353,7 +1353,7 @@ static void kvm_destroy_vm(struct kvm *kvm)
#endif
kvm_arch_free_vm(kvm);
preempt_notifier_dec();
- hardware_disable_all();
+ kvm_disable_virtualization();
mmdrop(mm);
}
@@ -5502,7 +5502,7 @@ static DEFINE_PER_CPU(bool, hardware_enabled);
static DEFINE_MUTEX(kvm_usage_lock);
static int kvm_usage_count;
-static int hardware_enable_nolock(void)
+static int __kvm_enable_virtualization(void)
{
if (__this_cpu_read(hardware_enabled))
return 0;
@@ -5524,10 +5524,10 @@ static int kvm_online_cpu(unsigned int cpu)
* be enabled. Otherwise running VMs would encounter unrecoverable
* errors when scheduled to this CPU.
*/
- return hardware_enable_nolock();
+ return __kvm_enable_virtualization();
}
-static void hardware_disable_nolock(void *junk)
+static void __kvm_disable_virtualization(void *ign)
{
if (!__this_cpu_read(hardware_enabled))
return;
@@ -5539,7 +5539,7 @@ static void hardware_disable_nolock(void *junk)
static int kvm_offline_cpu(unsigned int cpu)
{
- hardware_disable_nolock(NULL);
+ __kvm_disable_virtualization(NULL);
return 0;
}
@@ -5558,7 +5558,7 @@ static void kvm_shutdown(void)
*/
pr_info("kvm: exiting hardware virtualization\n");
kvm_rebooting = true;
- on_each_cpu(hardware_disable_nolock, NULL, 1);
+ on_each_cpu(__kvm_disable_virtualization, NULL, 1);
}
static int kvm_suspend(void)
@@ -5574,7 +5574,7 @@ static int kvm_suspend(void)
lockdep_assert_not_held(&kvm_usage_lock);
lockdep_assert_irqs_disabled();
- hardware_disable_nolock(NULL);
+ __kvm_disable_virtualization(NULL);
return 0;
}
@@ -5583,7 +5583,7 @@ static void kvm_resume(void)
lockdep_assert_not_held(&kvm_usage_lock);
lockdep_assert_irqs_disabled();
- WARN_ON_ONCE(hardware_enable_nolock());
+ WARN_ON_ONCE(__kvm_enable_virtualization());
}
static struct syscore_ops kvm_syscore_ops = {
@@ -5592,7 +5592,7 @@ static struct syscore_ops kvm_syscore_ops = {
.shutdown = kvm_shutdown,
};
-static int hardware_enable_all(void)
+static int kvm_enable_virtualization(void)
{
int r;
@@ -5635,7 +5635,7 @@ static int hardware_enable_all(void)
return r;
}
-static void hardware_disable_all(void)
+static void kvm_disable_virtualization(void)
{
guard(mutex)(&kvm_usage_lock);
@@ -5646,12 +5646,12 @@ static void hardware_disable_all(void)
cpuhp_remove_state(CPUHP_AP_KVM_ONLINE);
}
#else /* CONFIG_KVM_GENERIC_HARDWARE_ENABLING */
-static int hardware_enable_all(void)
+static int kvm_enable_virtualization(void)
{
return 0;
}
-static void hardware_disable_all(void)
+static void kvm_disable_virtualization(void)
{
}
--
2.45.2.505.gda0bf45e8d-goog
Register KVM's cpuhp and syscore callback when enabling virtualization
in hardware instead of registering the callbacks during initialization,
and let the CPU up/down framework invoke the inner enable/disable
functions. Registering the callbacks during initialization makes things
more complex than they need to be, as KVM needs to be very careful about
handling races between enabling CPUs being onlined/offlined and hardware
being enabled/disabled.
Intel TDX support will require KVM to enable virtualization during KVM
initialization, i.e. will add another wrinkle to things, at which point
sorting out the potential races with kvm_usage_count would become even
more complex.
Note, using the cpuhp framework has a subtle behavioral change: enabling
will be done serially across all CPUs, whereas KVM currently sends an IPI
to all CPUs in parallel. While serializing virtualization enabling could
create undesirable latency, the issue is limited to creation of KVM's
first VM, and even that can be mitigated, e.g. by letting userspace force
virtualization to be enabled when KVM is initialized.
Cc: Chao Gao <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
---
virt/kvm/kvm_main.c | 174 ++++++++++++++++----------------------------
1 file changed, 61 insertions(+), 113 deletions(-)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index d9b0579d3eea..f6b114f42433 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -5502,7 +5502,7 @@ static DEFINE_PER_CPU(bool, hardware_enabled);
static DEFINE_MUTEX(kvm_usage_lock);
static int kvm_usage_count;
-static int __hardware_enable_nolock(void)
+static int hardware_enable_nolock(void)
{
if (__this_cpu_read(hardware_enabled))
return 0;
@@ -5517,34 +5517,18 @@ static int __hardware_enable_nolock(void)
return 0;
}
-static void hardware_enable_nolock(void *failed)
-{
- if (__hardware_enable_nolock())
- atomic_inc(failed);
-}
-
static int kvm_online_cpu(unsigned int cpu)
{
- int ret = 0;
-
/*
* Abort the CPU online process if hardware virtualization cannot
* be enabled. Otherwise running VMs would encounter unrecoverable
* errors when scheduled to this CPU.
*/
- mutex_lock(&kvm_usage_lock);
- if (kvm_usage_count)
- ret = __hardware_enable_nolock();
- mutex_unlock(&kvm_usage_lock);
- return ret;
+ return hardware_enable_nolock();
}
static void hardware_disable_nolock(void *junk)
{
- /*
- * Note, hardware_disable_all_nolock() tells all online CPUs to disable
- * hardware, not just CPUs that successfully enabled hardware!
- */
if (!__this_cpu_read(hardware_enabled))
return;
@@ -5555,78 +5539,10 @@ static void hardware_disable_nolock(void *junk)
static int kvm_offline_cpu(unsigned int cpu)
{
- mutex_lock(&kvm_usage_lock);
- if (kvm_usage_count)
- hardware_disable_nolock(NULL);
- mutex_unlock(&kvm_usage_lock);
+ hardware_disable_nolock(NULL);
return 0;
}
-static void hardware_disable_all_nolock(void)
-{
- BUG_ON(!kvm_usage_count);
-
- kvm_usage_count--;
- if (!kvm_usage_count)
- on_each_cpu(hardware_disable_nolock, NULL, 1);
-}
-
-static void hardware_disable_all(void)
-{
- cpus_read_lock();
- mutex_lock(&kvm_usage_lock);
- hardware_disable_all_nolock();
- mutex_unlock(&kvm_usage_lock);
- cpus_read_unlock();
-}
-
-static int hardware_enable_all(void)
-{
- atomic_t failed = ATOMIC_INIT(0);
- int r;
-
- /*
- * Do not enable hardware virtualization if the system is going down.
- * If userspace initiated a forced reboot, e.g. reboot -f, then it's
- * possible for an in-flight KVM_CREATE_VM to trigger hardware enabling
- * after kvm_reboot() is called. Note, this relies on system_state
- * being set _before_ kvm_reboot(), which is why KVM uses a syscore ops
- * hook instead of registering a dedicated reboot notifier (the latter
- * runs before system_state is updated).
- */
- if (system_state == SYSTEM_HALT || system_state == SYSTEM_POWER_OFF ||
- system_state == SYSTEM_RESTART)
- return -EBUSY;
-
- /*
- * When onlining a CPU, cpu_online_mask is set before kvm_online_cpu()
- * is called, and so on_each_cpu() between them includes the CPU that
- * is being onlined. As a result, hardware_enable_nolock() may get
- * invoked before kvm_online_cpu(), which also enables hardware if the
- * usage count is non-zero. Disable CPU hotplug to avoid attempting to
- * enable hardware multiple times.
- */
- cpus_read_lock();
- mutex_lock(&kvm_usage_lock);
-
- r = 0;
-
- kvm_usage_count++;
- if (kvm_usage_count == 1) {
- on_each_cpu(hardware_enable_nolock, &failed, 1);
-
- if (atomic_read(&failed)) {
- hardware_disable_all_nolock();
- r = -EBUSY;
- }
- }
-
- mutex_unlock(&kvm_usage_lock);
- cpus_read_unlock();
-
- return r;
-}
-
static void kvm_shutdown(void)
{
/*
@@ -5658,8 +5574,7 @@ static int kvm_suspend(void)
lockdep_assert_not_held(&kvm_usage_lock);
lockdep_assert_irqs_disabled();
- if (kvm_usage_count)
- hardware_disable_nolock(NULL);
+ hardware_disable_nolock(NULL);
return 0;
}
@@ -5668,8 +5583,7 @@ static void kvm_resume(void)
lockdep_assert_not_held(&kvm_usage_lock);
lockdep_assert_irqs_disabled();
- if (kvm_usage_count)
- WARN_ON_ONCE(__hardware_enable_nolock());
+ WARN_ON_ONCE(hardware_enable_nolock());
}
static struct syscore_ops kvm_syscore_ops = {
@@ -5677,6 +5591,60 @@ static struct syscore_ops kvm_syscore_ops = {
.resume = kvm_resume,
.shutdown = kvm_shutdown,
};
+
+static int hardware_enable_all(void)
+{
+ int r;
+
+ guard(mutex)(&kvm_usage_lock);
+
+ if (kvm_usage_count++)
+ return 0;
+
+ r = cpuhp_setup_state(CPUHP_AP_KVM_ONLINE, "kvm/cpu:online",
+ kvm_online_cpu, kvm_offline_cpu);
+ if (r)
+ goto err_cpuhp;
+
+ register_syscore_ops(&kvm_syscore_ops);
+
+ /*
+ * Undo virtualization enabling and bail if the system is going down.
+ * If userspace initiated a forced reboot, e.g. reboot -f, then it's
+ * possible for an in-flight operation to enable virtualization after
+ * syscore_shutdown() is called, i.e. without kvm_shutdown() being
+ * invoked. Note, this relies on system_state being set _before_
+ * kvm_shutdown(), e.g. to ensure either kvm_shutdown() is invoked
+ * or this CPU observes the impending shutdown. Which is why KVM uses
+ * a syscore ops hook instead of registering a dedicated reboot
+ * notifier (the latter runs before system_state is updated).
+ */
+ if (system_state == SYSTEM_HALT || system_state == SYSTEM_POWER_OFF ||
+ system_state == SYSTEM_RESTART) {
+ r = -EBUSY;
+ goto err_rebooting;
+ }
+
+ return 0;
+
+err_rebooting:
+ unregister_syscore_ops(&kvm_syscore_ops);
+ cpuhp_remove_state(CPUHP_AP_KVM_ONLINE);
+err_cpuhp:
+ --kvm_usage_count;
+ return r;
+}
+
+static void hardware_disable_all(void)
+{
+ guard(mutex)(&kvm_usage_lock);
+
+ if (--kvm_usage_count)
+ return;
+
+ unregister_syscore_ops(&kvm_syscore_ops);
+ cpuhp_remove_state(CPUHP_AP_KVM_ONLINE);
+}
#else /* CONFIG_KVM_GENERIC_HARDWARE_ENABLING */
static int hardware_enable_all(void)
{
@@ -6382,15 +6350,6 @@ int kvm_init(unsigned vcpu_size, unsigned vcpu_align, struct module *module)
int r;
int cpu;
-#ifdef CONFIG_KVM_GENERIC_HARDWARE_ENABLING
- r = cpuhp_setup_state_nocalls(CPUHP_AP_KVM_ONLINE, "kvm/cpu:online",
- kvm_online_cpu, kvm_offline_cpu);
- if (r)
- return r;
-
- register_syscore_ops(&kvm_syscore_ops);
-#endif
-
/* A kmem cache lets us meet the alignment requirements of fx_save. */
if (!vcpu_align)
vcpu_align = __alignof__(struct kvm_vcpu);
@@ -6401,10 +6360,8 @@ int kvm_init(unsigned vcpu_size, unsigned vcpu_align, struct module *module)
offsetofend(struct kvm_vcpu, stats_id)
- offsetof(struct kvm_vcpu, arch),
NULL);
- if (!kvm_vcpu_cache) {
- r = -ENOMEM;
- goto err_vcpu_cache;
- }
+ if (!kvm_vcpu_cache)
+ return -ENOMEM;
for_each_possible_cpu(cpu) {
if (!alloc_cpumask_var_node(&per_cpu(cpu_kick_mask, cpu),
@@ -6461,11 +6418,6 @@ int kvm_init(unsigned vcpu_size, unsigned vcpu_align, struct module *module)
for_each_possible_cpu(cpu)
free_cpumask_var(per_cpu(cpu_kick_mask, cpu));
kmem_cache_destroy(kvm_vcpu_cache);
-err_vcpu_cache:
-#ifdef CONFIG_KVM_GENERIC_HARDWARE_ENABLING
- unregister_syscore_ops(&kvm_syscore_ops);
- cpuhp_remove_state_nocalls(CPUHP_AP_KVM_ONLINE);
-#endif
return r;
}
EXPORT_SYMBOL_GPL(kvm_init);
@@ -6487,10 +6439,6 @@ void kvm_exit(void)
kmem_cache_destroy(kvm_vcpu_cache);
kvm_vfio_ops_exit();
kvm_async_pf_deinit();
-#ifdef CONFIG_KVM_GENERIC_HARDWARE_ENABLING
- unregister_syscore_ops(&kvm_syscore_ops);
- cpuhp_remove_state_nocalls(CPUHP_AP_KVM_ONLINE);
-#endif
kvm_irqfd_exit();
}
EXPORT_SYMBOL_GPL(kvm_exit);
--
2.45.2.505.gda0bf45e8d-goog
Add arch hooks that are invoked when KVM enables/disable virtualization.
x86 will use the hooks to register an "emergency disable" callback, which
is essentially an x86-specific shutdown notifier that is used when the
kernel is doing an emergency reboot/shutdown/kexec.
Add comments for the declarations to help arch code understand exactly
when the callbacks are invoked. Alternatively, the APIs themselves could
communicate most of the same info, but kvm_arch_pre_enable_virtualization()
and kvm_arch_post_disable_virtualization() are a bit cumbersome, and make
it a bit less obvious that they are intended to be implemented as a pair.
Reviewed-by: Chao Gao <[email protected]>
Reviewed-by: Kai Huang <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
---
include/linux/kvm_host.h | 14 ++++++++++++++
virt/kvm/kvm_main.c | 14 ++++++++++++++
2 files changed, 28 insertions(+)
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 96ad3e8b9ddb..12ef3beb4e47 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1514,6 +1514,20 @@ static inline void kvm_create_vcpu_debugfs(struct kvm_vcpu *vcpu) {}
#endif
#ifdef CONFIG_KVM_GENERIC_HARDWARE_ENABLING
+/*
+ * kvm_arch_{enable,disable}_virtualization() are called on one CPU, under
+ * kvm_usage_lock, immediately after/before 0=>1 and 1=>0 transitions of
+ * kvm_usage_count, i.e. at the beginning of the generic hardware enabling
+ * sequence, and at the end of the generic hardware disabling sequence.
+ */
+void kvm_arch_enable_virtualization(void);
+void kvm_arch_disable_virtualization(void);
+/*
+ * kvm_arch_hardware_{enable,disable}() are called on "every" CPU to do the
+ * actual twiddling of hardware bits. The hooks are called all online CPUs
+ * when KVM enables/disabled virtualization. Enabling/disabling is also done
+ * when a CPU is onlined/offlined (or Resumed/Suspended).
+ */
int kvm_arch_hardware_enable(void);
void kvm_arch_hardware_disable(void);
#endif
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 7bdd744e4821..e20189a89a64 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -5505,6 +5505,16 @@ static DEFINE_PER_CPU(bool, hardware_enabled);
static DEFINE_MUTEX(kvm_usage_lock);
static int kvm_usage_count;
+__weak void kvm_arch_enable_virtualization(void)
+{
+
+}
+
+__weak void kvm_arch_disable_virtualization(void)
+{
+
+}
+
static int __kvm_enable_virtualization(void)
{
if (__this_cpu_read(hardware_enabled))
@@ -5604,6 +5614,8 @@ static int kvm_enable_virtualization(void)
if (kvm_usage_count++)
return 0;
+ kvm_arch_enable_virtualization();
+
r = cpuhp_setup_state(CPUHP_AP_KVM_ONLINE, "kvm/cpu:online",
kvm_online_cpu, kvm_offline_cpu);
if (r)
@@ -5634,6 +5646,7 @@ static int kvm_enable_virtualization(void)
unregister_syscore_ops(&kvm_syscore_ops);
cpuhp_remove_state(CPUHP_AP_KVM_ONLINE);
err_cpuhp:
+ kvm_arch_disable_virtualization();
--kvm_usage_count;
return r;
}
@@ -5647,6 +5660,7 @@ static void kvm_disable_virtualization(void)
unregister_syscore_ops(&kvm_syscore_ops);
cpuhp_remove_state(CPUHP_AP_KVM_ONLINE);
+ kvm_arch_disable_virtualization();
}
static int kvm_init_virtualization(void)
--
2.45.2.505.gda0bf45e8d-goog
Add an off-by-default module param, enable_virt_at_load, to let userspace
force virtualization to be enabled in hardware when KVM is initialized,
i.e. just before /dev/kvm is exposed to userspace. Enabling virtualization
during KVM initialization allows userspace to avoid the additional latency
when creating/destroying the first/last VM. Now that KVM uses the cpuhp
framework to do per-CPU enabling, the latency could be non-trivial as the
cpuhup bringup/teardown is serialized across CPUs, e.g. the latency could
be problematic for use case that need to spin up VMs quickly.
Enabling virtualizaton during initialization will also allow KVM to setup
the Intel TDX Module, which requires VMX to be fully enabled, without
needing additional APIs to temporarily enable virtualization.
Signed-off-by: Sean Christopherson <[email protected]>
---
virt/kvm/kvm_main.c | 37 +++++++++++++++++++++++++++++++++++++
1 file changed, 37 insertions(+)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 98e52d12f137..7bdd744e4821 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -5495,6 +5495,9 @@ static struct miscdevice kvm_dev = {
};
#ifdef CONFIG_KVM_GENERIC_HARDWARE_ENABLING
+static bool enable_virt_at_load;
+module_param(enable_virt_at_load, bool, 0444);
+
__visible bool kvm_rebooting;
EXPORT_SYMBOL_GPL(kvm_rebooting);
@@ -5645,15 +5648,41 @@ static void kvm_disable_virtualization(void)
unregister_syscore_ops(&kvm_syscore_ops);
cpuhp_remove_state(CPUHP_AP_KVM_ONLINE);
}
+
+static int kvm_init_virtualization(void)
+{
+ if (enable_virt_at_load)
+ return kvm_enable_virtualization();
+
+ return 0;
+}
+
+static void kvm_uninit_virtualization(void)
+{
+ if (enable_virt_at_load)
+ kvm_disable_virtualization();
+
+ WARN_ON(kvm_usage_count);
+}
#else /* CONFIG_KVM_GENERIC_HARDWARE_ENABLING */
static int kvm_enable_virtualization(void)
{
return 0;
}
+static int kvm_init_virtualization(void)
+{
+ return 0;
+}
+
static void kvm_disable_virtualization(void)
{
+}
+
+static void kvm_uninit_virtualization(void)
+{
+
}
#endif /* CONFIG_KVM_GENERIC_HARDWARE_ENABLING */
@@ -6395,6 +6424,10 @@ int kvm_init(unsigned vcpu_size, unsigned vcpu_align, struct module *module)
kvm_gmem_init(module);
+ r = kvm_init_virtualization();
+ if (r)
+ goto err_virt;
+
/*
* Registration _must_ be the very last thing done, as this exposes
* /dev/kvm to userspace, i.e. all infrastructure must be setup!
@@ -6408,6 +6441,8 @@ int kvm_init(unsigned vcpu_size, unsigned vcpu_align, struct module *module)
return 0;
err_register:
+ kvm_uninit_virtualization();
+err_virt:
kvm_vfio_ops_exit();
err_vfio:
kvm_async_pf_deinit();
@@ -6433,6 +6468,8 @@ void kvm_exit(void)
*/
misc_deregister(&kvm_dev);
+ kvm_uninit_virtualization();
+
debugfs_remove_recursive(kvm_debugfs_dir);
for_each_possible_cpu(cpu)
free_cpumask_var(per_cpu(cpu_kick_mask, cpu));
--
2.45.2.505.gda0bf45e8d-goog
Define cpu_emergency_virt_cb even if the kernel is being built without KVM
support so that KVM can reference the typedef in asm/kvm_host.h without
needing yet more #ifdefs.
No functional change intended.
Acked-by: Kai Huang <[email protected]>
Reviewed-by: Chao Gao <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
---
arch/x86/include/asm/reboot.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/reboot.h b/arch/x86/include/asm/reboot.h
index 6536873f8fc0..d0ef2a678d66 100644
--- a/arch/x86/include/asm/reboot.h
+++ b/arch/x86/include/asm/reboot.h
@@ -25,8 +25,8 @@ void __noreturn machine_real_restart(unsigned int type);
#define MRR_BIOS 0
#define MRR_APM 1
-#if IS_ENABLED(CONFIG_KVM_INTEL) || IS_ENABLED(CONFIG_KVM_AMD)
typedef void (cpu_emergency_virt_cb)(void);
+#if IS_ENABLED(CONFIG_KVM_INTEL) || IS_ENABLED(CONFIG_KVM_AMD)
void cpu_emergency_register_virt_callback(cpu_emergency_virt_cb *callback);
void cpu_emergency_unregister_virt_callback(cpu_emergency_virt_cb *callback);
void cpu_emergency_disable_virtualization(void);
--
2.45.2.505.gda0bf45e8d-goog
Register the "disable virtualization in an emergency" callback just
before KVM enables virtualization in hardware, as there is no functional
need to keep the callbacks registered while KVM happens to be loaded, but
is inactive, i.e. if KVM hasn't enabled virtualization.
Note, unregistering the callback every time the last VM is destroyed could
have measurable latency due to the synchronize_rcu() needed to ensure all
references to the callback are dropped before KVM is unloaded. But the
latency should be a small fraction of the total latency of disabling
virtualization across all CPUs, and userspace can set enable_virt_at_load
to completely eliminate the runtime overhead.
Add a pointer in kvm_x86_ops to allow vendor code to provide its callback.
There is no reason to force vendor code to do the registration, and either
way KVM would need a new kvm_x86_ops hook.
Suggested-by: Kai Huang <[email protected]>
Reviewed-by: Chao Gao <[email protected]>
Reviewed-by: Kai Huang <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
---
arch/x86/include/asm/kvm_host.h | 3 +++
arch/x86/kvm/svm/svm.c | 5 +----
arch/x86/kvm/vmx/main.c | 2 ++
arch/x86/kvm/vmx/vmx.c | 6 +-----
arch/x86/kvm/vmx/x86_ops.h | 1 +
arch/x86/kvm/x86.c | 10 ++++++++++
6 files changed, 18 insertions(+), 9 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 5c0415899a07..a4444b43f575 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -36,6 +36,7 @@
#include <asm/kvm_page_track.h>
#include <asm/kvm_vcpu_regs.h>
#include <asm/hyperv-tlfs.h>
+#include <asm/reboot.h>
#define __KVM_HAVE_ARCH_VCPU_DEBUGFS
@@ -1626,6 +1627,8 @@ struct kvm_x86_ops {
int (*hardware_enable)(void);
void (*hardware_disable)(void);
+ cpu_emergency_virt_cb *emergency_disable;
+
void (*hardware_unsetup)(void);
bool (*has_emulated_msr)(struct kvm *kvm, u32 index);
void (*vcpu_after_set_cpuid)(struct kvm_vcpu *vcpu);
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index d33193d522e3..aa0aeb185d17 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4981,6 +4981,7 @@ static void *svm_alloc_apic_backing_page(struct kvm_vcpu *vcpu)
static struct kvm_x86_ops svm_x86_ops __initdata = {
.name = KBUILD_MODNAME,
+ .emergency_disable = svm_emergency_disable,
.check_processor_compatibility = svm_check_processor_compat,
.hardware_unsetup = svm_hardware_unsetup,
@@ -5416,8 +5417,6 @@ static struct kvm_x86_init_ops svm_init_ops __initdata = {
static void __svm_exit(void)
{
kvm_x86_vendor_exit();
-
- cpu_emergency_unregister_virt_callback(svm_emergency_disable);
}
static int __init svm_init(void)
@@ -5433,8 +5432,6 @@ static int __init svm_init(void)
if (r)
return r;
- cpu_emergency_register_virt_callback(svm_emergency_disable);
-
/*
* Common KVM initialization _must_ come last, after this, /dev/kvm is
* exposed to userspace!
diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
index d0e1a5b5c915..45d6b5ad2da3 100644
--- a/arch/x86/kvm/vmx/main.c
+++ b/arch/x86/kvm/vmx/main.c
@@ -25,6 +25,8 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
.hardware_enable = vmx_hardware_enable,
.hardware_disable = vmx_hardware_disable,
+ .emergency_disable = vmx_emergency_disable,
+
.has_emulated_msr = vmx_has_emulated_msr,
.vm_size = sizeof(struct kvm_vmx),
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 0e3aaf520db2..7edbd4e5758e 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -754,7 +754,7 @@ static int kvm_cpu_vmxoff(void)
return -EIO;
}
-static void vmx_emergency_disable(void)
+void vmx_emergency_disable(void)
{
int cpu = raw_smp_processor_id();
struct loaded_vmcs *v;
@@ -8603,8 +8603,6 @@ static void __vmx_exit(void)
{
allow_smaller_maxphyaddr = false;
- cpu_emergency_unregister_virt_callback(vmx_emergency_disable);
-
vmx_cleanup_l1d_flush();
}
@@ -8651,8 +8649,6 @@ static int __init vmx_init(void)
pi_init_cpu(cpu);
}
- cpu_emergency_register_virt_callback(vmx_emergency_disable);
-
vmx_check_vmcs12_offsets();
/*
diff --git a/arch/x86/kvm/vmx/x86_ops.h b/arch/x86/kvm/vmx/x86_ops.h
index 502704596c83..afddfe3747dd 100644
--- a/arch/x86/kvm/vmx/x86_ops.h
+++ b/arch/x86/kvm/vmx/x86_ops.h
@@ -15,6 +15,7 @@ void vmx_hardware_unsetup(void);
int vmx_check_processor_compat(void);
int vmx_hardware_enable(void);
void vmx_hardware_disable(void);
+void vmx_emergency_disable(void);
int vmx_vm_init(struct kvm *kvm);
void vmx_vm_destroy(struct kvm *kvm);
int vmx_vcpu_precreate(struct kvm *kvm);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 4157602c964e..e4bdb42a9b00 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -12478,6 +12478,16 @@ void kvm_vcpu_deliver_sipi_vector(struct kvm_vcpu *vcpu, u8 vector)
}
EXPORT_SYMBOL_GPL(kvm_vcpu_deliver_sipi_vector);
+void kvm_arch_enable_virtualization(void)
+{
+ cpu_emergency_register_virt_callback(kvm_x86_ops.emergency_disable);
+}
+
+void kvm_arch_disable_virtualization(void)
+{
+ cpu_emergency_unregister_virt_callback(kvm_x86_ops.emergency_disable);
+}
+
int kvm_arch_hardware_enable(void)
{
struct kvm *kvm;
--
2.45.2.505.gda0bf45e8d-goog
Enable virtualization when KVM loads by default, as doing so avoids the
potential runtime overhead associated with using the cpuhp framework to
enabling virtualization on each CPU.
Prior to commit 10474ae8945c ("KVM: Activate Virtualization On Demand"),
KVM _unconditionally_ enabled virtualization during load, i.e. there's no
fundamental reason KVM needs to dynamically toggle virtualization. These
days, the only known argument for not enabling virtualization is to allow
KVM to be autoloaded without blocking other out-of-tree hypervisors, and
such use cases can simply change the module param, e.g. via command line.
Note, the aforementioned commit also mentioned that enabling SVM (AMD's
virtualization extensions) can result in "using invalid TLB entries".
It's not clear whether the changelog was referring to a KVM bug, a CPU
bug, or something else entirely. Regardless, leaving virtualization off
by default is not a robust "fix", as any protection provided is lost the
instant userspace creates the first VM.
Suggested-by: Chao Gao <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
---
virt/kvm/kvm_main.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index e20189a89a64..1440c0a7c3c3 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -5495,7 +5495,7 @@ static struct miscdevice kvm_dev = {
};
#ifdef CONFIG_KVM_GENERIC_HARDWARE_ENABLING
-static bool enable_virt_at_load;
+static bool enable_virt_at_load = true;
module_param(enable_virt_at_load, bool, 0444);
__visible bool kvm_rebooting;
--
2.45.2.505.gda0bf45e8d-goog
On Fri, 2024-06-07 at 17:06 -0700, Sean Christopherson wrote:
> Register KVM's cpuhp and syscore callback when enabling virtualization
> in hardware instead of registering the callbacks during initialization,
> and let the CPU up/down framework invoke the inner enable/disable
> functions. Registering the callbacks during initialization makes things
> more complex than they need to be, as KVM needs to be very careful about
> handling races between enabling CPUs being onlined/offlined and hardware
> being enabled/disabled.
>
> Intel TDX support will require KVM to enable virtualization during KVM
> initialization, i.e. will add another wrinkle to things, at which point
> sorting out the potential races with kvm_usage_count would become even
> more complex.
>
> Note, using the cpuhp framework has a subtle behavioral change: enabling
> will be done serially across all CPUs, whereas KVM currently sends an IPI
> to all CPUs in parallel. While serializing virtualization enabling could
> create undesirable latency, the issue is limited to creation of KVM's
> first VM, and even that can be mitigated, e.g. by letting userspace force
> virtualization to be enabled when KVM is initialized.
>
> Cc: Chao Gao <[email protected]>
> Signed-off-by: Sean Christopherson <[email protected]>
> ---
>
Reviewed-by: Kai Huang <[email protected]>
On Fri, 2024-06-07 at 17:06 -0700, Sean Christopherson wrote:
> Register KVM's cpuhp and syscore callbacks when enabling virtualization in
> hardware, as the sole purpose of said callbacks is to disable and re-enable
> virtualization as needed.
>
> The primary motivation for this series is to simplify dealing with enabling
> virtualization for Intel's TDX, which needs to enable virtualization
> when kvm-intel.ko is loaded, i.e. long before the first VM is created. TDX
> doesn't _need_ to keep virtualization enabled, but doing so is much simpler
> for KVM (see patch 3).
>
> That said, this is a nice cleanup on its own, assuming I haven't broken
> something. By registering the callbacks on-demand, the callbacks themselves
> don't need to check kvm_usage_count, because their very existence implies a
> non-zero count.
>
>
For this series,
Acked-by: Kai Huang <[email protected]>