From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-oo1-f53.google.com (mail-oo1-f53.google.com [209.85.161.53]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5F03C224CE for ; Tue, 27 Feb 2024 17:13:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.161.53 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709053991; cv=none; b=Q+lqkNMHYMGWSnYeQDjdZwlpJdpQvr4LrfNBi9ItoP2kGqlkHr5quQa4aIG0gbpCMAqttVtc72EsEE/B2/jyEdt+BP/s+fY0+rICrmGxAm/2Kp4O6nuoCFw/LYUS8ttNC8vjfDkzydex5zcKx4Zh0GFOWLkZYQb7TJHGEDAqMvM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709053991; c=relaxed/simple; bh=SWlb2BlxVRz858KyACzU9TGdZmZCIXkEAFtIFfCbVDQ=; h=MIME-Version:References:In-Reply-To:From:Date:Message-ID:Subject: To:Cc:Content-Type; b=eHd5I/NIkE4HT1jp+mv5J6JzM/9v2M6emcvZeZwTubDxvRpzG7JJEVgQ70On9j2QM06aRelFIcYDKPF/CgtBJbmV1JOJGw4uLhmEhKGP3FBnHbVmFWaUZBQzujldSatqTpCy+AQL1uff36EgZRH6oGD2Ns86ScTkoJ4WdGluY3E= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=Fj9QyAmS; arc=none smtp.client-ip=209.85.161.53 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="Fj9QyAmS" Received: by mail-oo1-f53.google.com with SMTP id 006d021491bc7-5a078ac712eso1398487eaf.1 for ; Tue, 27 Feb 2024 09:13:09 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1709053988; x=1709658788; darn=vger.kernel.org; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:from:to:cc:subject:date :message-id:reply-to; bh=l4w4THpRXMgaO2N+PLLuITl0YtMqqfXqaqVn9NdnEso=; b=Fj9QyAmSsTiuHqlNFVYfzvBqc2Snd/wc5S3SGSU2tr5rQCtTCiVCDVkl7MdXYGi+/i sb/wPQQl7o/vcO9D0dgFqnETzRU81nHyFvcH+yZQcFqOaK0oSegjpJybrGLlQ0ZmSRH6 JsSuiEdx5BA1wfI5OJb40K+WbUdxUuuwbgUKO7Br74zzXA3vLmqpwzHT8Uj/szi0Uj1b 7OAxUpzsojhdvR94ZPSIrenKmA+EuJVxBf0Rt1IYC/WwEggfx+A9ksZORXvFW9N2EJkJ p85RkFOfHdmQSfl5LfKvBhTzXtR7YhB9ffofZ7FjT8yyUFEmKugFMZrObHf8jN/CKoRj CkjQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1709053988; x=1709658788; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=l4w4THpRXMgaO2N+PLLuITl0YtMqqfXqaqVn9NdnEso=; b=O6dW9ZGcqs1MY3L8ffPV5h72nQpoy6EuJM4UTq+BmpuBZPnAJ8cP9fZCyhTb9hLdH7 pldnAw4IkHEiRtAZ0QQNoTqVbHxrn38lSqE6O8vRFP4R2+8aJGYX3nkKDQBaT8JSdny2 PYlmtLfD0ZO9c1jJH4dEZfoTBDWgxG5OK1TC6VjIS5R9LiucvQgTLCdkrUB3E4E8LgsE CilM9AalnJ/Ky8agLALu89HjBMVB6K36t2J0vrd5ERmLxwdmDtLOi/VjC2/hHBOVeWKl tARFCftfvWt49UJQfsVgz/67x1cnTgIAJncbnPjjnfE2+IYcuc9aWLXYm98QTd8bD4br Eq3A== X-Gm-Message-State: AOJu0YzyhosAMQ6IHKKFX2L1YJi8kmKLNYpcD46p0GBCphfQ0SVkhahJ 2XZ6Ui+CzF2xYgoW+oMf2WxrvEHb0+/OxID0MroF6YgCwAx67fNUYlwDJEggZ5sJ6pzv0oR0/WO mgP51GA8yySWk/zjUxWfn3JYU9mRf3zbHJJdA X-Google-Smtp-Source: AGHT+IG4NLP9w08aTBX6ChmfOuNBrO//8IOWcDelgzmmzT45Z6RFkmBGUjqHH2I7/3vyEZJraFaKzHOfDRMNSwwlpGI= X-Received: by 2002:a05:6820:2c07:b0:5a0:651d:4238 with SMTP id dw7-20020a0568202c0700b005a0651d4238mr7449063oob.2.1709053988360; Tue, 27 Feb 2024 09:13:08 -0800 (PST) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20240213192340.2023366-1-avagin@google.com> In-Reply-To: <20240213192340.2023366-1-avagin@google.com> From: Andrei Vagin Date: Tue, 27 Feb 2024 09:12:55 -0800 Message-ID: Subject: Re: [PATCH v3] kvm/x86: allocate the write-tracking metadata on-demand To: Paolo Bonzini , Sean Christopherson Cc: linux-kernel@vger.kernel.org, x86@kernel.org, kvm@vger.kernel.org, Zhenyu Wang Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Hi Paolo and Sean, Can we move forward with this version? Do you have any other comments, suggestions? Thanks, Andrrei On Tue, Feb 13, 2024 at 11:23=E2=80=AFAM Andrei Vagin w= rote: > > The write-track is used externally only by the gpu/drm/i915 driver. > Currently, it is always enabled, if a kernel has been compiled with this > driver. > > Enabling the write-track mechanism adds a two-byte overhead per page acro= ss > all memory slots. It isn't significant for regular VMs. However in gVisor= , > where the entire process virtual address space is mapped into the VM, eve= n > with a 39-bit address space, the overhead amounts to 256MB. > > Rework the write-tracking mechanism to enable it on-demand in > kvm_page_track_register_notifier. > > Here is Sean's comment about the locking scheme: > > The only potential hiccup would be if taking slots_arch_lock would > deadlock, but it should be impossible for slots_arch_lock to be taken in > any other path that involves VFIO and/or KVMGT *and* can be coincident. > Except for kvm_arch_destroy_vm() (which deletes KVM's internal > memslots), slots_arch_lock is taken only through KVM ioctls(), and the > caller of kvm_page_track_register_notifier() *must* hold a reference to > the VM. > > Cc: Paolo Bonzini > Cc: Sean Christopherson > Cc: Zhenyu Wang > Co-developed-by: Sean Christopherson > Signed-off-by: Andrei Vagin > --- > v1: https://lore.kernel.org/lkml/ZcErs9rPqT09nNge@google.com/T/ > v2: allocate the write-tracking metadata on-demand > https://lore.kernel.org/kvm/20240206153405.489531-1-avagin@google.com= / > v3: explicitly track if there are *external* write tracking users. > > arch/x86/include/asm/kvm_host.h | 9 +++++ > arch/x86/kvm/mmu/page_track.c | 68 ++++++++++++++++++++++++++++++++- > 2 files changed, 75 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_h= ost.h > index d271ba20a0b2..a777ac77b3ea 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -1468,6 +1468,15 @@ struct kvm_arch { > */ > bool shadow_root_allocated; > > +#ifdef CONFIG_KVM_EXTERNAL_WRITE_TRACKING > + /* > + * If set, the VM has (or had) an external write tracking user, a= nd > + * thus all write tracking metadata has been allocated, even if K= VM > + * itself isn't using write tracking. > + */ > + bool external_write_tracking_enabled; > +#endif > + > #if IS_ENABLED(CONFIG_HYPERV) > hpa_t hv_root_tdp; > spinlock_t hv_root_tdp_lock; > diff --git a/arch/x86/kvm/mmu/page_track.c b/arch/x86/kvm/mmu/page_track.= c > index c87da11f3a04..f6448284c18e 100644 > --- a/arch/x86/kvm/mmu/page_track.c > +++ b/arch/x86/kvm/mmu/page_track.c > @@ -20,10 +20,23 @@ > #include "mmu_internal.h" > #include "page_track.h" > > +static bool kvm_external_write_tracking_enabled(struct kvm *kvm) > +{ > +#ifdef CONFIG_KVM_EXTERNAL_WRITE_TRACKING > + /* > + * Read external_write_tracking_enabled before related pointers. = Pairs > + * with the smp_store_release in kvm_page_track_write_tracking_en= able(). > + */ > + return smp_load_acquire(&kvm->arch.external_write_tracking_enable= d); > +#else > + return false; > +#endif > +} > + > bool kvm_page_track_write_tracking_enabled(struct kvm *kvm) > { > - return IS_ENABLED(CONFIG_KVM_EXTERNAL_WRITE_TRACKING) || > - !tdp_enabled || kvm_shadow_root_allocated(kvm); > + return kvm_external_write_tracking_enabled(kvm) || > + kvm_shadow_root_allocated(kvm) || !tdp_enabled; > } > > void kvm_page_track_free_memslot(struct kvm_memory_slot *slot) > @@ -153,6 +166,50 @@ int kvm_page_track_init(struct kvm *kvm) > return init_srcu_struct(&head->track_srcu); > } > > +static int kvm_enable_external_write_tracking(struct kvm *kvm) > +{ > + struct kvm_memslots *slots; > + struct kvm_memory_slot *slot; > + int r =3D 0, i, bkt; > + > + mutex_lock(&kvm->slots_arch_lock); > + > + /* > + * Check for *any* write tracking user (not just external users) = under > + * lock. This avoids unnecessary work, e.g. if KVM itself is usi= ng > + * write tracking, or if two external users raced when registerin= g. > + */ > + if (kvm_page_track_write_tracking_enabled(kvm)) > + goto out_success; > + > + for (i =3D 0; i < kvm_arch_nr_memslot_as_ids(kvm); i++) { > + slots =3D __kvm_memslots(kvm, i); > + kvm_for_each_memslot(slot, bkt, slots) { > + /* > + * Intentionally do NOT free allocations on failu= re to > + * avoid having to track which allocations were m= ade > + * now versus when the memslot was created. The > + * metadata is guaranteed to be freed when the sl= ot is > + * freed, and will be kept/used if userspace retr= ies > + * the failed ioctl() instead of killing the VM. > + */ > + r =3D kvm_page_track_write_tracking_alloc(slot); > + if (r) > + goto out_unlock; > + } > + } > + > +out_success: > + /* > + * Ensure that external_write_tracking_enabled becomes true stric= tly > + * after all the related pointers are set. > + */ > + smp_store_release(&kvm->arch.external_write_tracking_enabled, tru= e); > +out_unlock: > + mutex_unlock(&kvm->slots_arch_lock); > + return r; > +} > + > /* > * register the notifier so that event interception for the tracked gues= t > * pages can be received. > @@ -161,10 +218,17 @@ int kvm_page_track_register_notifier(struct kvm *kv= m, > struct kvm_page_track_notifier_node = *n) > { > struct kvm_page_track_notifier_head *head; > + int r; > > if (!kvm || kvm->mm !=3D current->mm) > return -ESRCH; > > + if (!kvm_external_write_tracking_enabled(kvm)) { > + r =3D kvm_enable_external_write_tracking(kvm); > + if (r) > + return r; > + } > + > kvm_get_kvm(kvm); > > head =3D &kvm->arch.track_notifier_head; > -- > 2.43.0.687.g38aa6559b0-goog >