From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pg1-f202.google.com (mail-pg1-f202.google.com [209.85.215.202]) (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 D02B03B293 for ; Wed, 20 Sep 2023 14:24:10 +0000 (UTC) Received: by mail-pg1-f202.google.com with SMTP id 41be03b00d2f7-577af72294bso5140733a12.2 for ; Wed, 20 Sep 2023 07:24:10 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1695219850; x=1695824650; darn=lists.linux.dev; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=DOI6e5Fz0eSccYOGv0a2XgOrMIQyrqURVkPdu4XpUSk=; b=dEG3WNERy4HwbO9yqo+GYQUHEbzZ9aDOa2nJ+uVA49gBJ+5ztlnBP7oPI9ht9s5T+m ORGNwjlXuDf5E3VgHDFfBw0frutBnJ6Wa66WQq8V77Sr2GV7bHFMFHdmr445a9Dyg+BT u9nQCtQfgEHOdJj/5i7jVQRYnuTN3H7VHJHkqDpdf2n4g9nrr0FrBAiW3fxuqfV3euiC pYVE2ccvAzXyb84zaq4+dhm0Eq9C51riV70b2g0JTWrvMDbbCH+5qHbZT8tNlGE6D2xZ OVEZoYj9tHDo1jMmx5XFqfTOVl+Xh1OoRMcYpCKZIyc0bds6YzYpnplSYkZTQdh7RciX dXgQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1695219850; x=1695824650; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=DOI6e5Fz0eSccYOGv0a2XgOrMIQyrqURVkPdu4XpUSk=; b=By/ADKFFyaPW9IOJy4REG8shNAYakFs64oSv7NKl28vL51JyAiSUcsFMmsNenhpBTG dREa3ve/IFIukT6W3LlHbfQ84nKR3caWNV6N2RJBryz+5ltq183OxG0nvylqJNmBmwKP fGE868pK/f6akM1AI4qlcyd0OcKXqVjZEgOf3RBlafnPc/Coyn7OBncJjxfdXrFehqMy VxIH7mHlFNvcIbQkkDPp4Zyfn8UA8G5GIhitO3kV/JyXf0Hql4BdBbThx+lKvvEYBWIr oq6MrVfCwUhFOXTDFA8tRrtjqrVAKK3oMuGe/WGxchNHySSqYfRkEy+pKcJsQfBrMNSN tpGA== X-Gm-Message-State: AOJu0YywY7zgxRxivOKeGXWlMOab55REVyoqwFUo4GOVwEYJelKu/AsG YvTUqyWzW+2Z2BqP8v5z3/CFwBsj9Pc= X-Google-Smtp-Source: AGHT+IG+7+KaIB01fLVIPGeb7tjb/zu/hrsNFs+xXo/mmyM/aDSVQYbb0kWI4ACm+gkgu18FM/xCEI0V+P0= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a17:902:f203:b0:1c0:ac09:4032 with SMTP id m3-20020a170902f20300b001c0ac094032mr25326plc.9.1695219850013; Wed, 20 Sep 2023 07:24:10 -0700 (PDT) Date: Wed, 20 Sep 2023 07:24:08 -0700 In-Reply-To: Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20230914015531.1419405-1-seanjc@google.com> <20230914015531.1419405-15-seanjc@google.com> Message-ID: Subject: Re: [RFC PATCH v12 14/33] KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for guest-specific backing memory From: Sean Christopherson To: Binbin Wu Cc: kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, Paolo Bonzini , Marc Zyngier , Oliver Upton , Huacai Chen , Michael Ellerman , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , "Matthew Wilcox (Oracle)" , Andrew Morton , Paul Moore , James Morris , "Serge E. Hallyn" , Chao Peng , Fuad Tabba , Jarkko Sakkinen , Anish Moorthy , Yu Zhang , Isaku Yamahata , Xu Yilun , Vlastimil Babka , Vishal Annapurve , Ackerley Tng , Maciej Szmigiero , David Hildenbrand , Quentin Perret , Michael Roth , Wang , Liam Merwick , Isaku Yamahata , "Kirill A . Shutemov" Content-Type: text/plain; charset="us-ascii" On Tue, Sep 19, 2023, Binbin Wu wrote: > > > On 9/14/2023 9:55 AM, Sean Christopherson wrote: > [...] > > + > > +static void kvm_gmem_invalidate_begin(struct kvm_gmem *gmem, pgoff_t start, > > + pgoff_t end) > > +{ > > + struct kvm_memory_slot *slot; > > + struct kvm *kvm = gmem->kvm; > > + unsigned long index; > > + bool flush = false; > > + > > + KVM_MMU_LOCK(kvm); > > + > > + kvm_mmu_invalidate_begin(kvm); > > + > > + xa_for_each_range(&gmem->bindings, index, slot, start, end - 1) { > > + pgoff_t pgoff = slot->gmem.pgoff; > > + > > + struct kvm_gfn_range gfn_range = { > > + .start = slot->base_gfn + max(pgoff, start) - pgoff, > > + .end = slot->base_gfn + min(pgoff + slot->npages, end) - pgoff, > > + .slot = slot, > > + .may_block = true, > > + }; > > + > > + flush |= kvm_mmu_unmap_gfn_range(kvm, &gfn_range); > > + } > > + > > + if (flush) > > + kvm_flush_remote_tlbs(kvm); > > + > > + KVM_MMU_UNLOCK(kvm); > > +} > > + > > +static void kvm_gmem_invalidate_end(struct kvm_gmem *gmem, pgoff_t start, > > + pgoff_t end) > > +{ > > + struct kvm *kvm = gmem->kvm; > > + > > + KVM_MMU_LOCK(kvm); > > + if (xa_find(&gmem->bindings, &start, end - 1, XA_PRESENT)) > > + kvm_mmu_invalidate_end(kvm); > kvm_mmu_invalidate_begin() is called unconditionally in > kvm_gmem_invalidate_begin(), > but kvm_mmu_invalidate_end() is not here. > This makes the kvm_gmem_invalidate_{begin, end}() calls asymmetric. Another ouch :-( And there should be no need to acquire mmu_lock() unconditionally, the inode's mutex protects the bindings, not mmu_lock. I'll get a fix posted today. I think KVM can also add a sanity check to detect unresolved invalidations, e.g. diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 7ba1ab1832a9..2a2d18070856 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1381,8 +1381,13 @@ static void kvm_destroy_vm(struct kvm *kvm) * No threads can be waiting in kvm_swap_active_memslots() as the * last reference on KVM has been dropped, but freeing * memslots would deadlock without this manual intervention. + * + * If the count isn't unbalanced, i.e. KVM did NOT unregister between + * a start() and end(), then there shouldn't be any in-progress + * invalidations. */ WARN_ON(rcuwait_active(&kvm->mn_memslots_update_rcuwait)); + WARN_ON(!kvm->mn_active_invalidate_count && kvm->mmu_invalidate_in_progress); kvm->mn_active_invalidate_count = 0; #else kvm_flush_shadow_all(kvm); or an alternative style if (kvm->mn_active_invalidate_count) kvm->mn_active_invalidate_count = 0; else WARN_ON(kvm->mmu_invalidate_in_progress) > > + KVM_MMU_UNLOCK(kvm); > > +} > > + > > +static long kvm_gmem_punch_hole(struct inode *inode, loff_t offset, loff_t len) > > +{ > > + struct list_head *gmem_list = &inode->i_mapping->private_list; > > + pgoff_t start = offset >> PAGE_SHIFT; > > + pgoff_t end = (offset + len) >> PAGE_SHIFT; > > + struct kvm_gmem *gmem; > > + > > + /* > > + * Bindings must stable across invalidation to ensure the start+end > > + * are balanced. > > + */ > > + filemap_invalidate_lock(inode->i_mapping); > > + > > + list_for_each_entry(gmem, gmem_list, entry) { > > + kvm_gmem_invalidate_begin(gmem, start, end); > > + kvm_gmem_invalidate_end(gmem, start, end); > > + } > Why to loop for each gmem in gmem_list here? > > IIUIC, offset is the offset according to the inode, it is only meaningful to > the inode passed in, i.e, it is only meaningful to the gmem binding with the > inode, not others. The code is structured to allow for multiple gmem instances per inode. This isn't actually possible in the initial code base, but it's on the horizon[*]. I included the list-based infrastructure in this initial series to ensure that guest_memfd can actually support multiple files per inode, and to minimize the churn when the "link" support comes along. [*] https://lore.kernel.org/all/cover.1691446946.git.ackerleytng@google.com