From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 829DFC433F5 for ; Tue, 12 Apr 2022 12:41:20 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id D3F9C6B0082; Tue, 12 Apr 2022 08:41:19 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id CF0296B0083; Tue, 12 Apr 2022 08:41:19 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B69A96B0085; Tue, 12 Apr 2022 08:41:19 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0079.hostedemail.com [216.40.44.79]) by kanga.kvack.org (Postfix) with ESMTP id A67B26B0082 for ; Tue, 12 Apr 2022 08:41:19 -0400 (EDT) Received: from smtpin25.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 5651F183BFA96 for ; Tue, 12 Apr 2022 12:41:19 +0000 (UTC) X-FDA: 79348187478.25.2C2ED1B Received: from mga12.intel.com (mga12.intel.com [192.55.52.136]) by imf13.hostedemail.com (Postfix) with ESMTP id 4206820002 for ; Tue, 12 Apr 2022 12:41:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1649767278; x=1681303278; h=date:from:to:cc:subject:message-id:reply-to:references: mime-version:in-reply-to; bh=eyXblfG/A5HWVja7fFUb4HNY/ZRRmFMXW6QIdjEei/o=; b=nBuWCpYiiQsOF01H7ERKR+ACY5XIApEmuE6jt/1Sr4uzeYp6bCYFVMkX sAbXHroCAFUk8QUTWDjd36i2Ozc5d1BhJPBMtfHi0gl5PHZkIB82UWpiY 6KP3VOnkMD4JCCHjiXo7G1cEwcbOItFbmuoYRzP6kmLOylypSHH8FjtzN Vr4+wZs3suphvogfgCkED+30IEFiI+/KUUnlnLme4GLvmx4jvJt+B3W0L krLLLTqIWIRSzbClSdzj95ac5WaKl0v9DFAth+iN90lVJOIAEG6jdqJd0 7USSQF0EvUEhFpgnQfWtLovkTEk1fJhWB6gmbAnmqrhWqizhFz99G/Sue w==; X-IronPort-AV: E=McAfee;i="6400,9594,10314"; a="242305241" X-IronPort-AV: E=Sophos;i="5.90,253,1643702400"; d="scan'208";a="242305241" Received: from orsmga002.jf.intel.com ([10.7.209.21]) by fmsmga106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Apr 2022 05:41:15 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.90,253,1643702400"; d="scan'208";a="526023841" Received: from chaop.bj.intel.com (HELO localhost) ([10.240.192.101]) by orsmga002.jf.intel.com with ESMTP; 12 Apr 2022 05:41:06 -0700 Date: Tue, 12 Apr 2022 20:40:56 +0800 From: Chao Peng To: Sean Christopherson Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, qemu-devel@nongnu.org, Paolo Bonzini , Jonathan Corbet , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H . Peter Anvin" , Hugh Dickins , Jeff Layton , "J . Bruce Fields" , Andrew Morton , Mike Rapoport , Steven Price , "Maciej S . Szmigiero" , Vlastimil Babka , Vishal Annapurve , Yu Zhang , "Kirill A . Shutemov" , luto@kernel.org, jun.nakajima@intel.com, dave.hansen@intel.com, ak@linux.intel.com, david@redhat.com Subject: Re: [PATCH v5 10/13] KVM: Register private memslot to memory backing store Message-ID: <20220412124056.GA8013@chaop.bj.intel.com> Reply-To: Chao Peng References: <20220310140911.50924-1-chao.p.peng@linux.intel.com> <20220310140911.50924-11-chao.p.peng@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 4206820002 X-Rspam-User: Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=intel.com header.s=Intel header.b=nBuWCpYi; dmarc=pass (policy=none) header.from=intel.com; spf=none (imf13.hostedemail.com: domain of chao.p.peng@linux.intel.com has no SPF policy when checking 192.55.52.136) smtp.mailfrom=chao.p.peng@linux.intel.com X-Stat-Signature: 6rkaqap1dm5gyfrc48n79ktiz36ra461 X-HE-Tag: 1649767277-191387 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Mar 29, 2022 at 07:01:52PM +0000, Sean Christopherson wrote: > On Thu, Mar 10, 2022, Chao Peng wrote: > > Add 'notifier' to memslot to make it a memfile_notifier node and then > > register it to memory backing store via memfile_register_notifier() when > > memslot gets created. When memslot is deleted, do the reverse with > > memfile_unregister_notifier(). Note each KVM memslot can be registered > > to different memory backing stores (or the same backing store but at > > different offset) independently. > > > > Signed-off-by: Yu Zhang > > Signed-off-by: Chao Peng > > --- > > include/linux/kvm_host.h | 1 + > > virt/kvm/kvm_main.c | 75 ++++++++++++++++++++++++++++++++++++---- > > 2 files changed, 70 insertions(+), 6 deletions(-) > > > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > > index 6e1d770d6bf8..9b175aeca63f 100644 > > --- a/include/linux/kvm_host.h > > +++ b/include/linux/kvm_host.h > > @@ -567,6 +567,7 @@ struct kvm_memory_slot { > > struct file *private_file; > > loff_t private_offset; > > struct memfile_pfn_ops *pfn_ops; > > + struct memfile_notifier notifier; > > }; > > > > static inline bool kvm_slot_is_private(const struct kvm_memory_slot *slot) > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > > index d11a2628b548..67349421eae3 100644 > > --- a/virt/kvm/kvm_main.c > > +++ b/virt/kvm/kvm_main.c > > @@ -840,6 +840,37 @@ static int kvm_init_mmu_notifier(struct kvm *kvm) > > > > #endif /* CONFIG_MMU_NOTIFIER && KVM_ARCH_WANT_MMU_NOTIFIER */ > > > > +#ifdef CONFIG_MEMFILE_NOTIFIER > > +static inline int kvm_memfile_register(struct kvm_memory_slot *slot) > > This is a good oppurtunity to hide away the memfile details a bit. Maybe > kvm_private_mem_{,un}register()? Happy to change. > > > +{ > > + return memfile_register_notifier(file_inode(slot->private_file), > > + &slot->notifier, > > + &slot->pfn_ops); > > +} > > + > > +static inline void kvm_memfile_unregister(struct kvm_memory_slot *slot) > > +{ > > + if (slot->private_file) { > > + memfile_unregister_notifier(file_inode(slot->private_file), > > + &slot->notifier); > > + fput(slot->private_file); > > This should not do fput(), it makes the helper imbalanced with respect to the > register path and will likely lead to double fput(). Indeed, if preparing the > region fails, __kvm_set_memory_region() will double up on fput() due to checking > its local "file" for null, not slot->private for null. Right. > > > + slot->private_file = NULL; > > + } > > +} > > + > > +#else /* !CONFIG_MEMFILE_NOTIFIER */ > > + > > +static inline int kvm_memfile_register(struct kvm_memory_slot *slot) > > +{ > > This should WARN_ON_ONCE(). Ditto for unregister. > > > + return -EOPNOTSUPP; > > +} > > + > > +static inline void kvm_memfile_unregister(struct kvm_memory_slot *slot) > > +{ > > +} > > + > > +#endif /* CONFIG_MEMFILE_NOTIFIER */ > > + > > #ifdef CONFIG_HAVE_KVM_PM_NOTIFIER > > static int kvm_pm_notifier_call(struct notifier_block *bl, > > unsigned long state, > > @@ -884,6 +915,9 @@ static void kvm_destroy_dirty_bitmap(struct kvm_memory_slot *memslot) > > /* This does not remove the slot from struct kvm_memslots data structures */ > > static void kvm_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot) > > { > > + if (slot->flags & KVM_MEM_PRIVATE) > > + kvm_memfile_unregister(slot); > > With fput() move out of unregister, this needs to be: Agreed. > > if (slot->flags & KVM_MEM_PRIVATE) { > kvm_private_mem_unregister(slot); > fput(slot->private_file); > } > > + > > kvm_destroy_dirty_bitmap(slot); > > > > kvm_arch_free_memslot(kvm, slot); > > @@ -1738,6 +1772,12 @@ static int kvm_set_memslot(struct kvm *kvm, > > kvm_invalidate_memslot(kvm, old, invalid_slot); > > } > > > > + if (new->flags & KVM_MEM_PRIVATE && change == KVM_MR_CREATE) { > > + r = kvm_memfile_register(new); > > + if (r) > > + return r; > > + } > > This belongs in kvm_prepare_memory_region(). The shenanigans for DELETE and MOVE > are special. Sure. > > > + > > r = kvm_prepare_memory_region(kvm, old, new, change); > > if (r) { > > /* > > @@ -1752,6 +1792,10 @@ static int kvm_set_memslot(struct kvm *kvm, > > } else { > > mutex_unlock(&kvm->slots_arch_lock); > > } > > + > > + if (new->flags & KVM_MEM_PRIVATE && change == KVM_MR_CREATE) > > + kvm_memfile_unregister(new); > > + > > return r; > > } > > > > @@ -1817,6 +1861,7 @@ int __kvm_set_memory_region(struct kvm *kvm, > > enum kvm_mr_change change; > > unsigned long npages; > > gfn_t base_gfn; > > + struct file *file = NULL; > > Nit, naming this private_file would help understand its use. Though I think it's > easier to not have a local variable. More below. > > > int as_id, id; > > int r; > > > > @@ -1890,14 +1935,24 @@ int __kvm_set_memory_region(struct kvm *kvm, > > return 0; > > } > > > > + if (mem->flags & KVM_MEM_PRIVATE) { > > + file = fdget(region_ext->private_fd).file; > > This can use fget() instead of fdget(). > > > + if (!file) > > + return -EINVAL; > > + } > > + > > if ((change == KVM_MR_CREATE || change == KVM_MR_MOVE) && > > - kvm_check_memslot_overlap(slots, id, base_gfn, base_gfn + npages)) > > - return -EEXIST; > > + kvm_check_memslot_overlap(slots, id, base_gfn, base_gfn + npages)) { > > + r = -EEXIST; > > + goto out; > > + } > > > > /* Allocate a slot that will persist in the memslot. */ > > new = kzalloc(sizeof(*new), GFP_KERNEL_ACCOUNT); > > - if (!new) > > - return -ENOMEM; > > + if (!new) { > > + r = -ENOMEM; > > + goto out; > > + } > > > > new->as_id = as_id; > > new->id = id; > > @@ -1905,10 +1960,18 @@ int __kvm_set_memory_region(struct kvm *kvm, > > new->npages = npages; > > new->flags = mem->flags; > > new->userspace_addr = mem->userspace_addr; > > + new->private_file = file; > > + new->private_offset = mem->flags & KVM_MEM_PRIVATE ? > > + region_ext->private_offset : 0; > > "new" is zero-allocated, so all the private stuff, including the fget(), can be > wrapped in a single KVM_MEM_PRIVATE check. Moving fget() eliminates the number > of gotos needed (the above -EEXIST and -ENOMEM paths don't need to be modified). > > > r = kvm_set_memslot(kvm, old, new, change); > > - if (r) > > - kfree(new); > > + if (!r) > > + return r; > > Use goto, e.g. > > if (r) > goto out; > > return 0; > > Burying the happy path in a taken if-statement is confusing and error prone, > mostly because it breaks well-established kernel patterns. Note, there's no need > for a separate out_free since new->private_file will be NULL in either case. I > don't have a strong preference, I just find it easier to read code that's more > explicit, but I'm a-ok collapsing them into a single label. Will follow this, thanks for the detailed suggestion. Chao > > if ((change == KVM_MR_CREATE || change == KVM_MR_MOVE) && > kvm_check_memslot_overlap(slots, id, base_gfn, base_gfn + npages)) > return -EEXIST; > > /* Allocate a slot that will persist in the memslot. */ > new = kzalloc(sizeof(*new), GFP_KERNEL_ACCOUNT); > if (!new) > return -ENOMEM; > > new->as_id = as_id; > new->id = id; > new->base_gfn = base_gfn; > new->npages = npages; > new->flags = mem->flags; > new->userspace_addr = mem->userspace_addr; > > if (mem->flags & KVM_MEM_PRIVATE) { > new->private_file = fget(mem->private_fd); > if (!new->private_file) { > r = -EINVAL; > goto out_free; > } > new->private_offset = mem->private_offset; > } > > r = kvm_set_memslot(kvm, old, new, change); > if (r) > goto out; > > return 0; > > out: > if (new->private_file) > fput(new->private_file); > > out_free: > kfree(new); > return r;