Subject: [PATCH v10 04/18] KVM: arm/arm64: Introduce kvm_arch_vcpu_run_pid_change

From: [email-masked] (Alex Bennée)
Date: Wed, 23 May 2018 15:34:20 +0100

Dave Martin <[email-masked]> writes:

> From: Christoffer Dall <[email-masked]>
>
> KVM/ARM differs from other architectures in having to maintain an
> additional virtual address space from that of the host and the
> guest, because we split the execution of KVM across both EL1 and
> EL2.
>
> This results in a need to explicitly map data structures into EL2
> (hyp) which are accessed from the hyp code.  As we are about to be
> more clever with our FPSIMD handling on arm64, which stores data in
> the task struct and uses thread_info flags, we will have to map
> parts of the currently executing task struct into the EL2 virtual
> address space.
>
> However, we don't want to do this on every KVM_RUN, because it is a
> fairly expensive operation to walk the page tables, and the common
> execution mode is to map a single thread to a VCPU.  By introducing
> a hook that architectures can select with
> HAVE_KVM_VCPU_RUN_PID_CHANGE, we do not introduce overhead for
> other architectures, but have a simple way to only map the data we
> need when required for arm64.
>
> This patch introduces the framework only, and wires it up in the
> arm/arm64 KVM common code.
>
> No functional change.
>
> Signed-off-by: Christoffer Dall <[email-masked]>
> Signed-off-by: Dave Martin <[email-masked]>
> Reviewed-by: Marc Zyngier <[email-masked]>
> ---
>  include/linux/kvm_host.h | 9 +++++++++
>  virt/kvm/Kconfig         | 3 +++
>  virt/kvm/kvm_main.c      | 7 ++++++-
>  3 files changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 6930c63..4268ace 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -1276,4 +1276,13 @@ static inline long kvm_arch_vcpu_async_ioctl(struct file *filp,
>  void kvm_arch_mmu_notifier_invalidate_range(struct kvm *kvm,
>  		unsigned long start, unsigned long end);
>
> +#ifdef CONFIG_HAVE_KVM_VCPU_RUN_PID_CHANGE
> +int kvm_arch_vcpu_run_pid_change(struct kvm_vcpu *vcpu);
> +#else
> +static inline int kvm_arch_vcpu_run_pid_change(struct kvm_vcpu *vcpu)
> +{
> +	return 0;
> +}
> +#endif /* CONFIG_HAVE_KVM_VCPU_RUN_PID_CHANGE */
> +
>  #endif
> diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
> index cca7e06..72143cf 100644
> --- a/virt/kvm/Kconfig
> +++ b/virt/kvm/Kconfig
> @@ -54,3 +54,6 @@ config HAVE_KVM_IRQ_BYPASS
>
>  config HAVE_KVM_VCPU_ASYNC_IOCTL
>         bool
> +
> +config HAVE_KVM_VCPU_RUN_PID_CHANGE
> +       bool

This almost threw me as I thought you might be able to enable this and
break the build, but apparently not:

Reviewed-by: Alex Benn?e <[email-masked]>

> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index c7b2e92..c32e240 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2550,8 +2550,13 @@ static long kvm_vcpu_ioctl(struct file *filp,
>  		oldpid = rcu_access_pointer(vcpu->pid);
>  		if (unlikely(oldpid != current->pids[PIDTYPE_PID].pid)) {
>  			/* The thread running this VCPU changed. */
> -			struct pid *newpid = get_task_pid(current, PIDTYPE_PID);
> +			struct pid *newpid;
>
> +			r = kvm_arch_vcpu_run_pid_change(vcpu);
> +			if (r)
> +				break;
> +
> +			newpid = get_task_pid(current, PIDTYPE_PID);
>  			rcu_assign_pointer(vcpu->pid, newpid);
>  			if (oldpid)
>  				synchronize_rcu();

--
Alex Benn?e