Re: [PATCH v3 11/22] KVM: Add arch hooks for PM events with empty stub

[Isaku Yamahata]

On Tue, Sep 06, 2022 at 02:25:02PM +0800,
Yuan Yao <yuan.yao@xxxxxxxxxxxxxxx> wrote:

> On Thu, Sep 01, 2022 at 07:17:46PM -0700, isaku.yamahata@xxxxxxxxx wrote:
> > From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> >
> > Add arch hooks for reboot, suspend, resume, and CPU-online/offline events
> > with empty stub functions.
> >
> > Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> > Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> > ---
> >  include/linux/kvm_host.h |  6 +++++
> >  virt/kvm/Makefile.kvm    |  2 +-
> >  virt/kvm/kvm_arch.c      | 44 +++++++++++++++++++++++++++++++++++
> >  virt/kvm/kvm_main.c      | 50 +++++++++++++++++++++++++---------------
> >  4 files changed, 82 insertions(+), 20 deletions(-)
> >  create mode 100644 virt/kvm/kvm_arch.c
> >
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index eab352902de7..dd2a6d98d4de 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -1448,6 +1448,12 @@ int kvm_arch_post_init_vm(struct kvm *kvm);
> >  void kvm_arch_pre_destroy_vm(struct kvm *kvm);
> >  int kvm_arch_create_vm_debugfs(struct kvm *kvm);
> >
> > +int kvm_arch_suspend(int usage_count);
> > +void kvm_arch_resume(int usage_count);
> > +int kvm_arch_reboot(int val);
> > +int kvm_arch_online_cpu(unsigned int cpu, int usage_count);
> > +int kvm_arch_offline_cpu(unsigned int cpu, int usage_count);
> > +
> >  #ifndef __KVM_HAVE_ARCH_VM_ALLOC
> >  /*
> >   * All architectures that want to use vzalloc currently also
> > diff --git a/virt/kvm/Makefile.kvm b/virt/kvm/Makefile.kvm
> > index 2c27d5d0c367..c4210acabd35 100644
> > --- a/virt/kvm/Makefile.kvm
> > +++ b/virt/kvm/Makefile.kvm
> > @@ -5,7 +5,7 @@
> >
> >  KVM ?= ../../../virt/kvm
> >
> > -kvm-y := $(KVM)/kvm_main.o $(KVM)/eventfd.o $(KVM)/binary_stats.o
> > +kvm-y := $(KVM)/kvm_main.o $(KVM)/kvm_arch.o $(KVM)/eventfd.o $(KVM)/binary_stats.o
> >  kvm-$(CONFIG_KVM_VFIO) += $(KVM)/vfio.o
> >  kvm-$(CONFIG_KVM_MMIO) += $(KVM)/coalesced_mmio.o
> >  kvm-$(CONFIG_KVM_ASYNC_PF) += $(KVM)/async_pf.o
> > diff --git a/virt/kvm/kvm_arch.c b/virt/kvm/kvm_arch.c
> > new file mode 100644
> > index 000000000000..4748a76bcb03
> > --- /dev/null
> > +++ b/virt/kvm/kvm_arch.c
> > @@ -0,0 +1,44 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/*
> > + * kvm_arch.c: kvm default arch hooks for hardware enabling/disabling
> > + * Copyright (c) 2022 Intel Corporation.
> > + *
> > + * Author:
> > + *   Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> > + *                  <isaku.yamahata@xxxxxxxxx>
> > + */
> > +
> > +#include <linux/kvm_host.h>
> > +
> > +/*
> > + * Called after the VM is otherwise initialized, but just before adding it to
> > + * the vm_list.
> > + */
> > +__weak int kvm_arch_post_init_vm(struct kvm *kvm)
> > +{
> > +	return 0;
> > +}
> > +
> > +__weak int kvm_arch_online_cpu(unsigned int cpu, int usage_count)
> > +{
> > +	return 0;
> > +}
> > +
> > +__weak int kvm_arch_offline_cpu(unsigned int cpu, int usage_count)
> > +{
> > +	return 0;
> > +}
> > +
> > +__weak int kvm_arch_reboot(int val)
> > +{
> > +	return NOTIFY_OK;
> > +}
> > +
> > +__weak int kvm_arch_suspend(int usage_count)
> > +{
> > +	return 0;
> > +}
> > +
> > +__weak void kvm_arch_resume(int usage_count)
> > +{
> > +}
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index 082d5dbc8d7f..e62240fb8474 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -144,6 +144,7 @@ static int kvm_no_compat_open(struct inode *inode, struct file *file)
> >  #endif
> >  static int hardware_enable_all(void);
> >  static void hardware_disable_all(void);
> > +static void hardware_disable_nolock(void *junk);
> >
> >  static void kvm_io_bus_destroy(struct kvm_io_bus *bus);
> >
> > @@ -1097,15 +1098,6 @@ static int kvm_create_vm_debugfs(struct kvm *kvm, const char *fdname)
> >  	return ret;
> >  }
> >
> > -/*
> > - * Called after the VM is otherwise initialized, but just before adding it to
> > - * the vm_list.
> > - */
> > -int __weak kvm_arch_post_init_vm(struct kvm *kvm)
> > -{
> > -	return 0;
> > -}
> > -
> >  /*
> >   * Called just after removing the VM from the vm_list, but before doing any
> >   * other destruction.
> > @@ -5033,6 +5025,10 @@ static int kvm_online_cpu(unsigned int cpu)
> >  		if (atomic_read(&hardware_enable_failed)) {
> >  			atomic_set(&hardware_enable_failed, 0);
> >  			ret = -EIO;
> > +		} else {
> > +			ret = kvm_arch_online_cpu(cpu, kvm_usage_count);
> > +			if (ret)
> > +				hardware_disable_nolock(NULL);
> >  		}
> >  	}
> >  	mutex_unlock(&kvm_lock);
> > @@ -5053,11 +5049,19 @@ static void hardware_disable_nolock(void *junk)
> >
> >  static int kvm_offline_cpu(unsigned int cpu)
> >  {
> > +	int ret = 0;
> > +
> >  	mutex_lock(&kvm_lock);
> > -	if (kvm_usage_count)
> > +	if (kvm_usage_count) {
> >  		hardware_disable_nolock(NULL);
> > +		ret = kvm_arch_offline_cpu(cpu, kvm_usage_count);
> > +		if (ret) {
> > +			(void)hardware_enable_nolock(NULL);
> > +			atomic_set(&hardware_enable_failed, 0);
> > +		}
> > +	}
> >  	mutex_unlock(&kvm_lock);
> > -	return 0;
> > +	return ret;
> >  }
> >
> >  static void hardware_disable_all_nolock(void)
> > @@ -5115,6 +5119,8 @@ static int hardware_enable_all(void)
> >  static int kvm_reboot(struct notifier_block *notifier, unsigned long val,
> >  		      void *v)
> >  {
> > +	int r;
> > +
> >  	/*
> >  	 * Some (well, at least mine) BIOSes hang on reboot if
> >  	 * in vmx root mode.
> > @@ -5123,8 +5129,15 @@ static int kvm_reboot(struct notifier_block *notifier, unsigned long val,
> >  	 */
> >  	pr_info("kvm: exiting hardware virtualization\n");
> >  	kvm_rebooting = true;
> > +
> > +	/* This hook is called without cpuhotplug disabled.  */
> > +	cpus_read_lock();
> > +	mutex_lock(&kvm_lock);
> >  	on_each_cpu(hardware_disable_nolock, NULL, 1);
> > -	return NOTIFY_OK;
> > +	r = kvm_arch_reboot(val);
> > +	mutex_unlock(&kvm_lock);
> > +	cpus_read_unlock();
> > +	return r;
> >  }
> >
> >  static struct notifier_block kvm_reboot_notifier = {
> > @@ -5718,11 +5731,10 @@ static int kvm_suspend(void)
> >  	 * cpu_hotplug_disable() and other CPUs are offlined.  No need for
> >  	 * locking.
> >  	 */
> > -	if (kvm_usage_count) {
> > -		lockdep_assert_not_held(&kvm_lock);
> > +	lockdep_assert_not_held(&kvm_lock);
> > +	if (kvm_usage_count)
> >  		hardware_disable_nolock(NULL);
> > -	}
> > -	return 0;
> > +	return kvm_arch_suspend(kvm_usage_count);
> >  }
> >
> e  static void kvm_resume(void)
> > @@ -5734,10 +5746,10 @@ static void kvm_resume(void)
> >  		 */
> >  		return; /* FIXME: disable KVM */
> >
> > -	if (kvm_usage_count) {
> > -		lockdep_assert_not_held(&kvm_lock);
> > +	lockdep_assert_not_held(&kvm_lock);
> > +	kvm_arch_resume(kvm_usage_count);
> > +	if (kvm_usage_count)
> >  		hardware_enable_nolock((void *)__func__);
> 
> Is single kvm_arch_{suspend,resume} enough?
> 
> The sequence is:
> 
> kvm_arch_resume()
> hardware_enable_nolock()
> 
> But in patch 12 I see below code in x86's kvm_arch_resume():
> ...
> if (!usage_count)
>         return;
> if (kvm_arch_hardware_enable())
>         return;
> ...
> 
> So kvm_arch_resume() may depend on hardware enable, and it checks the
> usage_count again, how about call kvm_arch_resume(bool
> hardware_enabled) before/after the hardware_enable_nolock() (or even
> give different functions with _before/_after suffix) for better
> flexibility since it's common code for all architectures, e.g.
> 
> if (kvm_usage_count) {
>    kvm_arch_resume(false);
>    hardware_enable_nolock(__func__);
>    kvm_arch_resumt(true);
> }

Nice catch.  I fixed it as follows.

kvm_resume()
  if (kvm_usage_count)
      hardware_enable_nolock()
  kvm_arch_resume()

x86 kvm_arch_resume() doesn't call hardware_enable().
The patch of adjust compatibility check and hardware_enable().
-- 
Isaku Yamahata <isaku.yamahata@xxxxxxxxx>