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AFNElJ9fghlGqGvxXjuiD3Bi4WX0Z+KbQZnnlhfpX5gu0C+Gj28G0SgHCVd9RR36Ph8fdvAlHLKlmDlTpw==@kvack.org X-Gm-Message-State: AOJu0Yx7Vlwux9WVk4hutXmvEdcHOTJ2TJSNT/bdUZhrzgRm5PF8oBXe hhNKX1DouwvUpOYXjClLuR+hVywIFbk1lsha+egFpdR4HtDCpuGYUh05JCVGGnUEOlq3iwiFdq5 oP2UCOA== X-Received: from pghz21.prod.google.com ([2002:a63:e115:0:b0:c7f:c4f1:ae17]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a20:7349:b0:3a3:17f8:bedd with SMTP id adf61e73a8af0-3b22ea4f434mr28099153637.17.1779309551955; Wed, 20 May 2026 13:39:11 -0700 (PDT) Date: Wed, 20 May 2026 13:39:11 -0700 In-Reply-To: Mime-Version: 1.0 References: <20260507-gmem-inplace-conversion-v6-0-91ab5a8b19a4@google.com> <20260507-gmem-inplace-conversion-v6-6-91ab5a8b19a4@google.com> Message-ID: Subject: Re: [PATCH v6 06/43] KVM: x86/mmu: Bug the VM if gmem attributes are queried to determine max mapping level From: Sean Christopherson To: Ackerley Tng Cc: Fuad Tabba , aik@amd.com, andrew.jones@linux.dev, binbin.wu@linux.intel.com, brauner@kernel.org, chao.p.peng@linux.intel.com, david@kernel.org, ira.weiny@intel.com, jmattson@google.com, jthoughton@google.com, michael.roth@amd.com, oupton@kernel.org, pankaj.gupta@amd.com, qperret@google.com, rick.p.edgecombe@intel.com, rientjes@google.com, shivankg@amd.com, steven.price@arm.com, willy@infradead.org, wyihan@google.com, yan.y.zhao@intel.com, forkloop@google.com, pratyush@kernel.org, suzuki.poulose@arm.com, aneesh.kumar@kernel.org, liam@infradead.org, Paolo Bonzini , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Jonathan Corbet , Shuah Khan , Shuah Khan , Vishal Annapurve , Andrew Morton , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Youngjun Park , Qi Zheng , Shakeel Butt , Kiryl Shutsemau , Jason Gunthorpe , Vlastimil Babka , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, linux-coco@lists.linux.dev Content-Type: text/plain; charset="us-ascii" X-Stat-Signature: 7djhz6as7ewi49is7dephadp35icxk19 X-Rspamd-Queue-Id: D0DB31A000B X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1779309553-713611 X-HE-Meta: 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 w5H4FFI6 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, May 20, 2026, Ackerley Tng wrote: > Sean Christopherson writes: > >> > } else { > >> > + /* > >> > + * Memory attributes cannot be obtained from guest_memfd while > >> > + * the MMU lock is held. > >> > + */ > >> > + if (KVM_BUG_ON(static_call_query(__kvm_get_memory_attributes) == > >> > + kvm_gmem_get_memory_attributes, kvm)) { > >> > + return 0; > >> > + } > >> > + > >> > >> This directly takes the address of kvm_gmem_get_memory_attributes, > >> which is only compiled if CONFIG_KVM_GUEST_MEMFD=y. This breaks > >> ARCH=i386. > > > > And this bleeds guest_memfd implementation details into places they don't belong. > > The right way to deal with this is to use lockdep_assert_not_held() in whatever > > code mustn't run with mmu_lock held. E.g. > > > > diff --git virt/kvm/guest_memfd.c virt/kvm/guest_memfd.c > > index c9f155c2dc5c..3bea9c1137ef 100644 > > --- virt/kvm/guest_memfd.c > > +++ virt/kvm/guest_memfd.c > > @@ -547,6 +547,9 @@ unsigned long kvm_gmem_get_memory_attributes(struct kvm *kvm, gfn_t gfn) > > struct kvm_memory_slot *slot = gfn_to_memslot(kvm, gfn); > > struct inode *inode; > > > > + /* Comment goes here. */ > > + lockdep_assert_not_held(&kvm->mmu_lock); > > + > > /* > > * If this gfn has no associated memslot, there's no chance of the gfn > > * being backed by private memory, since guest_memfd must be used for > > > > But I'm confused, because kvm_gmem_get_memory_attributes() doesn't actually take > > filemap_invalidate_lock(), so what exactly is the problem? > > > > Ahh I can drop this patch now. kvm_gmem_get_memory_attributes() used to > take the filemap_invalidate_lock(), but after Liam pointed out that > the attributes maple tree should be using MT_FLAGS_USE_RCU, I stopped > taking filemap_invalidate_lock() and forgot to undo this. > > I'll wait a bit for more reviews and then put out another revision > without this patch. If this is the only issue with v6, don't send a new version, I'll just drop it when applying.