6.12-stable review patch. If anyone has any objections, please let me know.
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From: Keith Busch kbusch@kernel.org
commit 931656b9e2ff7029aee0b36e17780621948a6ac1 upstream.
Some libraries want to ensure they are single threaded before forking, so making the kernel's kvm huge page recovery process a vhost task of the user process breaks those. The minijail library used by crosvm is one such affected application.
Defer the task to after the first VM_RUN call, which occurs after the parent process has forked all its jailed processes. This needs to happen only once for the kvm instance, so introduce some general-purpose infrastructure for that, too. It's similar in concept to pthread_once; except it is actually usable, because the callback takes a parameter.
Cc: Sean Christopherson seanjc@google.com Cc: Paolo Bonzini pbonzini@redhat.com Tested-by: Alyssa Ross hi@alyssa.is Signed-off-by: Keith Busch kbusch@kernel.org Message-ID: 20250123153543.2769928-1-kbusch@meta.com [Move call_once API to include/linux. - Paolo] Cc: stable@vger.kernel.org Fixes: d96c77bd4eeb ("KVM: x86: switch hugepage recovery thread to vhost_task") Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/include/asm/kvm_host.h | 2 + arch/x86/kvm/mmu/mmu.c | 18 +++++++++++----- arch/x86/kvm/x86.c | 7 +++++- include/linux/call_once.h | 45 ++++++++++++++++++++++++++++++++++++++++ 4 files changed, 66 insertions(+), 6 deletions(-) create mode 100644 include/linux/call_once.h
--- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -27,6 +27,7 @@ #include <linux/hyperv.h> #include <linux/kfifo.h> #include <linux/sched/vhost_task.h> +#include <linux/call_once.h>
#include <asm/apic.h> #include <asm/pvclock-abi.h> @@ -1446,6 +1447,7 @@ struct kvm_arch { struct kvm_x86_pmu_event_filter __rcu *pmu_event_filter; struct vhost_task *nx_huge_page_recovery_thread; u64 nx_huge_page_last; + struct once nx_once;
#ifdef CONFIG_X86_64 /* The number of TDP MMU pages across all roots. */ --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -7565,20 +7565,28 @@ static bool kvm_nx_huge_page_recovery_wo return true; }
-int kvm_mmu_post_init_vm(struct kvm *kvm) +static void kvm_mmu_start_lpage_recovery(struct once *once) { - if (nx_hugepage_mitigation_hard_disabled) - return 0; + struct kvm_arch *ka = container_of(once, struct kvm_arch, nx_once); + struct kvm *kvm = container_of(ka, struct kvm, arch);
kvm->arch.nx_huge_page_last = get_jiffies_64(); kvm->arch.nx_huge_page_recovery_thread = vhost_task_create( kvm_nx_huge_page_recovery_worker, kvm_nx_huge_page_recovery_worker_kill, kvm, "kvm-nx-lpage-recovery");
+ if (kvm->arch.nx_huge_page_recovery_thread) + vhost_task_start(kvm->arch.nx_huge_page_recovery_thread); +} + +int kvm_mmu_post_init_vm(struct kvm *kvm) +{ + if (nx_hugepage_mitigation_hard_disabled) + return 0; + + call_once(&kvm->arch.nx_once, kvm_mmu_start_lpage_recovery); if (!kvm->arch.nx_huge_page_recovery_thread) return -ENOMEM; - - vhost_task_start(kvm->arch.nx_huge_page_recovery_thread); return 0; }
--- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -11478,6 +11478,10 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_v struct kvm_run *kvm_run = vcpu->run; int r;
+ r = kvm_mmu_post_init_vm(vcpu->kvm); + if (r) + return r; + vcpu_load(vcpu); kvm_sigset_activate(vcpu); kvm_run->flags = 0; @@ -12751,7 +12755,8 @@ out:
int kvm_arch_post_init_vm(struct kvm *kvm) { - return kvm_mmu_post_init_vm(kvm); + once_init(&kvm->arch.nx_once); + return 0; }
static void kvm_unload_vcpu_mmu(struct kvm_vcpu *vcpu) --- /dev/null +++ b/include/linux/call_once.h @@ -0,0 +1,45 @@ +#ifndef _LINUX_CALL_ONCE_H +#define _LINUX_CALL_ONCE_H + +#include <linux/types.h> +#include <linux/mutex.h> + +#define ONCE_NOT_STARTED 0 +#define ONCE_RUNNING 1 +#define ONCE_COMPLETED 2 + +struct once { + atomic_t state; + struct mutex lock; +}; + +static inline void __once_init(struct once *once, const char *name, + struct lock_class_key *key) +{ + atomic_set(&once->state, ONCE_NOT_STARTED); + __mutex_init(&once->lock, name, key); +} + +#define once_init(once) \ +do { \ + static struct lock_class_key __key; \ + __once_init((once), #once, &__key); \ +} while (0) + +static inline void call_once(struct once *once, void (*cb)(struct once *)) +{ + /* Pairs with atomic_set_release() below. */ + if (atomic_read_acquire(&once->state) == ONCE_COMPLETED) + return; + + guard(mutex)(&once->lock); + WARN_ON(atomic_read(&once->state) == ONCE_RUNNING); + if (atomic_read(&once->state) != ONCE_NOT_STARTED) + return; + + atomic_set(&once->state, ONCE_RUNNING); + cb(once); + atomic_set_release(&once->state, ONCE_COMPLETED); +} + +#endif /* _LINUX_CALL_ONCE_H */