Dave Martin <dave.mar...@arm.com> writes:
> From: Christoffer Dall <christoffer.d...@linaro.org>
>
> 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 <christoffer.d...@linaro.org>
> Signed-off-by: Dave Martin <dave.mar...@arm.com>
> Reviewed-by: Marc Zyngier <marc.zyng...@arm.com>
> ---
> 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 Bennée <alex.ben...@linaro.org>
> 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 Bennée
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