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AJvYcCUMsLY7KwQ2KHlNL4V2jAkXPIp/qOxBghVql47SOTl8zOo6OItiPlwrBZswW+joKWw1fTN+e3TGyQ==@kvack.org X-Gm-Message-State: AOJu0YwEN/2xffcBlXY7Cp0IQo44pyOwRcZFtvjs0bKk1I26zihUyqmg eGk3zhQVr2As11wMDnrUKaIgEtpQxyMMeRTFMqKetkoSHOA5VgClIYPUZMjI7EmIbwWut85plDh z65IT3+HztLMSGM6exeUXsg5caw== X-Google-Smtp-Source: AGHT+IHSCWEZ4WzQFvfM7gmfwowerM9ooYJUxTCTTxPR6qD/XE6Y7uX4MPuDDOyY1Umu3SEnPhVG+BTFarjXCQhhaQ== X-Received: from pjboi8.prod.google.com ([2002:a17:90b:3a08:b0:321:90c5:fc2b]) (user=ackerleytng job=prod-delivery.src-stubby-dispatcher) by 2002:a17:902:ef0f:b0:240:b075:577f with SMTP id d9443c01a7336-244586c4da1mr76912365ad.37.1755207307282; Thu, 14 Aug 2025 14:35:07 -0700 (PDT) Date: Thu, 14 Aug 2025 14:35:05 -0700 In-Reply-To: Mime-Version: 1.0 References: Message-ID: Subject: Re: [RFC PATCH v2 02/51] KVM: guest_memfd: Introduce and use shareability to guard faulting From: Ackerley Tng To: Yan Zhao Cc: kvm@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, x86@kernel.org, linux-fsdevel@vger.kernel.org, aik@amd.com, ajones@ventanamicro.com, akpm@linux-foundation.org, amoorthy@google.com, anthony.yznaga@oracle.com, anup@brainfault.org, aou@eecs.berkeley.edu, bfoster@redhat.com, binbin.wu@linux.intel.com, brauner@kernel.org, catalin.marinas@arm.com, chao.p.peng@intel.com, chenhuacai@kernel.org, dave.hansen@intel.com, david@redhat.com, dmatlack@google.com, dwmw@amazon.co.uk, erdemaktas@google.com, fan.du@intel.com, fvdl@google.com, graf@amazon.com, haibo1.xu@intel.com, hch@infradead.org, hughd@google.com, ira.weiny@intel.com, isaku.yamahata@intel.com, jack@suse.cz, james.morse@arm.com, jarkko@kernel.org, jgg@ziepe.ca, jgowans@amazon.com, jhubbard@nvidia.com, jroedel@suse.de, jthoughton@google.com, jun.miao@intel.com, kai.huang@intel.com, keirf@google.com, kent.overstreet@linux.dev, kirill.shutemov@intel.com, liam.merwick@oracle.com, maciej.wieczor-retman@intel.com, mail@maciej.szmigiero.name, maz@kernel.org, mic@digikod.net, michael.roth@amd.com, mpe@ellerman.id.au, muchun.song@linux.dev, nikunj@amd.com, nsaenz@amazon.es, oliver.upton@linux.dev, palmer@dabbelt.com, pankaj.gupta@amd.com, paul.walmsley@sifive.com, pbonzini@redhat.com, pdurrant@amazon.co.uk, peterx@redhat.com, pgonda@google.com, pvorel@suse.cz, qperret@google.com, quic_cvanscha@quicinc.com, quic_eberman@quicinc.com, quic_mnalajal@quicinc.com, quic_pderrin@quicinc.com, quic_pheragu@quicinc.com, quic_svaddagi@quicinc.com, quic_tsoni@quicinc.com, richard.weiyang@gmail.com, rick.p.edgecombe@intel.com, rientjes@google.com, roypat@amazon.co.uk, rppt@kernel.org, seanjc@google.com, shuah@kernel.org, steven.price@arm.com, steven.sistare@oracle.com, suzuki.poulose@arm.com, tabba@google.com, thomas.lendacky@amd.com, usama.arif@bytedance.com, vannapurve@google.com, vbabka@suse.cz, viro@zeniv.linux.org.uk, vkuznets@redhat.com, wei.w.wang@intel.com, will@kernel.org, willy@infradead.org, xiaoyao.li@intel.com, yilun.xu@intel.com, yuzenghui@huawei.com, zhiquan1.li@intel.com Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: B4765A000D X-Stat-Signature: gybibioc3h91k3rrmu6x67m6n9a51nm3 X-Rspam-User: X-HE-Tag: 1755207308-133557 X-HE-Meta: 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 BcFgfdF9 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 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: List-Subscribe: List-Unsubscribe: Yan Zhao writes: > On Wed, May 14, 2025 at 04:41:41PM -0700, Ackerley Tng wrote: >> +static enum shareability kvm_gmem_shareability_get(struct inode *inode, >> + pgoff_t index) >> +{ >> + struct maple_tree *mt; >> + void *entry; >> + >> + mt = &kvm_gmem_private(inode)->shareability; >> + entry = mtree_load(mt, index); >> + WARN(!entry, >> + "Shareability should always be defined for all indices in inode."); >> + >> + return xa_to_value(entry); >> +} >> + > Hi Ackerley, > > Not sure if it's a known issue. Just want to let you know in case you're unaware. > Thanks for informing me, and thanks for the analysis :) > During a test to repeatedly launching/destroying TDs, I encountered a warning > from kvm_gmem_shareability_get() (see the attached log at the bottom). > The reproducing rate is 1 in every 20-100 times of launching TD. > > After some analysis, I found that the warning was produced by > kvm_gmem_shareability_get() when it's called from kvm_gmem_is_private(), which > is not protected by any locks. > > I can get rid of the warning by either fix 1 or fix 2 below. > (I prefer fix 1 though :)) > > fix 1: > > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > index e78fbebf4f53..136d46c5b2ab 100644 > --- a/virt/kvm/guest_memfd.c > +++ b/virt/kvm/guest_memfd.c > @@ -2024,7 +2024,7 @@ static struct inode *kvm_gmem_inode_make_secure_inode(const char *name, > > #ifdef CONFIG_KVM_GMEM_SHARED_MEM > if (flags & GUEST_MEMFD_FLAG_SUPPORT_SHARED) { > - mt_init(&private->shareability); > + mt_init_flags(&private->shareability, MT_FLAGS_USE_RCU); > > err = kvm_gmem_shareability_setup(private, size, flags); > if (err) > Not sure about the version of the conversion patch series that you're using, in the version I'm preparing, I'm using filemap_invalidate_lock_shared() to guard shareability reads. filemap_invalidate_lock() is held during shareability updates, so I think this issue should be fixed. Please let me know if you're still seeing this issue in the next series (coming soon). Thank you! > > fix 2: > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > index e78fbebf4f53..9a4518104d56 100644 > --- a/virt/kvm/guest_memfd.c > +++ b/virt/kvm/guest_memfd.c > @@ -171,7 +171,9 @@ static enum shareability kvm_gmem_shareability_get(struct inode *inode, > void *entry; > > mt = &kvm_gmem_private(inode)->shareability; > + mtree_lock(mt); > entry = mtree_load(mt, index); > + mtree_unlock(mt); > WARN(!entry, > "Shareability should always be defined for all indices in inode."); > > > Thanks > Yan > > > [...snip...] >