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X-CSE-ConnectionGUID: zJtaUR/oQuqDzdsl4TrvVA== X-CSE-MsgGUID: 12byxQ6zQyaBQ3984MavyQ== X-IronPort-AV: E=McAfee;i="6800,10657,11887"; a="75839234" X-IronPort-AV: E=Sophos;i="6.25,246,1779174000"; d="scan'208";a="75839234" Received: from fmviesa004.fm.intel.com ([10.60.135.144]) by fmvoesa110.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 26 Aug 2026 21:34:28 -0700 X-CSE-ConnectionGUID: rV3cStscS/aNLMyWraRS+w== X-CSE-MsgGUID: WvkBd7g8TtuwCi4hAeOL8Q== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.25,246,1779174000"; d="scan'208";a="269701976" Received: from xiaoyaol-hp-g830.ccr.corp.intel.com (HELO [10.124.240.119]) ([10.124.240.119]) by fmviesa004-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 26 Aug 2026 21:34:14 -0700 Message-ID: Date: Thu, 27 Aug 2026 12:34:11 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v10 09/41] KVM: guest_memfd: Filter both shared and private when invalidating To: Sean Christopherson , Ackerley Tng Cc: Michael Roth , Suzuki K Poulose , "David Hildenbrand (Arm)" , aik@amd.com, andrew.jones@linux.dev, binbin.wu@linux.intel.com, brauner@kernel.org, chao.p.peng@linux.intel.com, jmattson@google.com, jthoughton@google.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, tabba@google.com, willy@infradead.org, wyihan@google.com, yan.y.zhao@intel.com, forkloop@google.com, pratyush@kernel.org, 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 , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Youngjun Park , Qi Zheng , Shakeel Butt , Kiryl Shutsemau , Baoquan He , Jason Gunthorpe , John Hubbard , Peter Xu , tarunsahu@google.com, 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 References: <20260807-gmem-inplace-conversion-v10-9-2fc18ee6d3ba@google.com> <13ca60c6-e154-4397-8092-09f861e90fe0@kernel.org> <7eba513d-cdae-4832-abac-038dcdd88517@intel.com> Content-Language: en-US From: Xiaoyao Li In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 4D730100004 X-Stat-Signature: y1z5bmhq7kpymuznmweyjfatmn8emyqd X-HE-Tag: 1787805270-915281 X-HE-Meta: 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 /JshcEaF miXl1ld/yFRBmp+5z2JrD4KobvSlL91vkbc6WEfo6/3SKIixp04M1ox4Nwb1mZok6mez5e28iETBz4CgKCfXni1LUcqM+6KI90acdxX1EYw/eM/zGvMNyp63l0KWoSt99MnPM+eRjMZzfjWpdBmI8zh9/cwJQqC24j8qFHPty8a8RLIpZ/vD9SsazWd6vTqb0IKB/lGDIQnADvd9mmhQ5VwWU7wi6oECJzqpn39es377PjxnlYh/RvjX39hT2/884yhGHF+4v2JI9BPswUEROnDb58X+MDDnxgDpaYlAvkAhzldE= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/26/2026 9:53 PM, Sean Christopherson wrote: >> Is this just a case of user error? That with gmem_in_place_conversion, >> userspace should not use userspace_addr from something other than the >> gmem for the same memslot? > > Yes. It's not just invalidations that will go sideways, > KVM accesses to guest > memory won't hit the same physical page as actual guest accesses. Side topic. If KVM enforces KVM_MEMSLOT_GMEM_ONLY when gmem_in_place_conversion is true like below proposal, should we update KVM's guest memory accessors to access gmem directly? If still use the existing code of accessing userspace_addr of the memslot, I think KVM needs to document clearly that when KVM_CAP_GUEST_MEMFD_MEMORY_ATTRIBUTES is enumerated, if configuring the guest_memfd for a memslot, the userspace_addr passed in needs to be the mmaped address of the guest_memfd. > Huh. But that isn't strictly guaranteed, because userspace could bind to a > memslot that isn't configured with GUEST_MEMFD_FLAG_MMAP, in which case SHARED > faults will go through the VMA, not kvm_mmu_faultin_pfn_gmem(). It's a bit early > in the morning, but off the top of my head, I can't think of any reason we need > to support such a setup. If userspace really, really wants to use a separate > mapping, they could DELETE+CREATE an equivalent memslot without the guest_memfd > file descriptor. > > So I think we should do this? > > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > index 9c2d52bdf25e..86f53e53a136 100644 > --- a/virt/kvm/guest_memfd.c > +++ b/virt/kvm/guest_memfd.c > @@ -1013,7 +1013,7 @@ int kvm_gmem_bind(struct kvm *kvm, struct kvm_memory_slot *slot, > */ > WRITE_ONCE(slot->gmem.file, file); > slot->gmem.pgoff = start; > - if (kvm_gmem_supports_mmap(inode)) > + if (gmem_in_place_conversion || kvm_gmem_supports_mmap(inode)) > slot->flags |= KVM_MEMSLOT_GMEM_ONLY; I like this idea. It makes gmem_in_place_conversion a step closer to what its name implies, though in-place conversion is not truly 100% guaranteed[*]. [*] https://lore.kernel.org/all/akUbz_kJvYulaboo@google.com/ > xa_store_range(&f->bindings, start, end - 1, slot, GFP_KERNEL); > > Regardless, the key aspect of all this is that in-place conversion is brand new > functionality, so we don't have to ensure backwards compatibility.