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X-CSE-ConnectionGUID: jepbuVVgQsC22RNXIzQPIw== X-CSE-MsgGUID: q08kxDkjSCi0O8psoCC0Cw== X-IronPort-AV: E=McAfee;i="6800,10657,11863"; a="90143903" X-IronPort-AV: E=Sophos;i="6.25,201,1779174000"; d="scan'208";a="90143903" Received: from fmviesa003.fm.intel.com ([10.60.135.143]) by orvoesa106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 02 Aug 2026 19:43:44 -0700 X-CSE-ConnectionGUID: BEG4ZP1DRymmaTKVaWpetA== X-CSE-MsgGUID: B7M1+kP7TIiUCgGwEr8Lcw== X-ExtLoop1: 1 Received: from xiaoyaol-hp-g830.ccr.corp.intel.com (HELO [10.124.240.248]) ([10.124.240.248]) by fmviesa003-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 02 Aug 2026 19:43:30 -0700 Message-ID: <25ab36cf-888a-4547-b3f7-5bd4e057c1d0@intel.com> Date: Mon, 3 Aug 2026 10:43:26 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v9 07/41] KVM: guest_memfd: Wire up core private/shared attribute interfaces To: Sean Christopherson Cc: Ackerley Tng , aik@amd.com, andrew.jones@linux.dev, binbin.wu@linux.intel.com, brauner@kernel.org, chao.p.peng@linux.intel.com, david@kernel.org, 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, tabba@google.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 , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Youngjun Park , Qi Zheng , Shakeel Butt , Kiryl Shutsemau , Baoquan He , Jason Gunthorpe , John Hubbard , Peter Xu , 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: <20260728-gmem-inplace-conversion-v9-0-35f9aec2aed2@google.com> <20260728-gmem-inplace-conversion-v9-7-35f9aec2aed2@google.com> <60d19013-d6d7-4eec-827a-2622e22cec98@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-Stat-Signature: yqtmwpmdx4ox54fjqi3jx4tsuynx47zx X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 7A8FD40002 X-Rspam-User: X-HE-Tag: 1785725025-693096 X-HE-Meta: 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 vKJfslZx IIe3jGfw8IaWWmsIY9CHjCV5UhsBElXaQRbJ+ps3SkOfKOegOsAEy3JJx/zyg8Ht165X66Y+lLDYJqIeVAOPnxk2m6FdA8TfBpAl6esiL6IJ2wDmwTXcfEBIw/2+uTPXtg5ZHHEWr2HMyO7ZvFbXeFZNSfKVMygA/xNWOQGQRlda3vHK7r8F+RH2kvgAWlJ3BsAGrAbER4qjk9JvrK+b00yImEK4GEVsMGThRQ9jjF0gK7M+BWlnEj35TOFFv/LiJODVYopEw7RwUhCbj9NizDOrxFg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/1/2026 12:26 AM, Sean Christopherson wrote: > On Fri, Jul 31, 2026, Xiaoyao Li wrote: >> On 7/31/2026 4:42 AM, Ackerley Tng wrote: >>> Xiaoyao Li writes: >>> >>>> On 7/29/2026 8:35 AM, Ackerley Tng via B4 Relay wrote: >>>>> diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c >>>>> index 33c9830190e2e..89cf922232920 100644 >>>>> --- a/virt/kvm/guest_memfd.c >>>>> +++ b/virt/kvm/guest_memfd.c >>>>> @@ -893,6 +893,27 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot, >>>>> EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_gmem_get_pfn); >>>>> >>>>> #ifdef CONFIG_HAVE_KVM_ARCH_GMEM_POPULATE >>>>> +static bool kvm_range_is_private(struct file *file, pgoff_t index, >>>>> + size_t nr_pages, struct kvm *kvm, gfn_t gfn) >>>>> +{ >>>>> + struct inode *inode = file_inode(file); >>>>> + pgoff_t last = index + nr_pages - 1; >>>>> + struct maple_tree *mt; >>>>> + void *entry; >>>>> + >>>>> + if (!gmem_in_place_conversion) >>>>> + return kvm_range_has_vm_memory_attributes(kvm, gfn, gfn + nr_pages, >>>>> + KVM_MEMORY_ATTRIBUTE_PRIVATE, >>>>> + KVM_MEMORY_ATTRIBUTE_PRIVATE); >>>>> + >>>>> + mt = &GMEM_I(inode)->attributes; >>>>> + mt_for_each(mt, entry, index, last) { >>>>> + if (kvm_gmem_interpret_entry(inode, entry) != >>>>> + KVM_MEMORY_ATTRIBUTE_PRIVATE) >>>>> + return false; >>>>> + } >>>>> + return true; >>>>> +} >>>>> >>>>> static long __kvm_gmem_populate(struct kvm *kvm, struct kvm_memory_slot *slot, >>>>> struct file *file, gfn_t gfn, struct page *src_page, >>>>> @@ -913,9 +934,7 @@ static long __kvm_gmem_populate(struct kvm *kvm, struct kvm_memory_slot *slot, >>>>> >>>>> folio_unlock(folio); >>>>> >>>>> - if (!kvm_range_has_vm_memory_attributes(kvm, gfn, gfn + 1, >>>>> - KVM_MEMORY_ATTRIBUTE_PRIVATE, >>>>> - KVM_MEMORY_ATTRIBUTE_PRIVATE)) { >>>>> + if (!kvm_range_is_private(file, index, 1, kvm, gfn)) { >>>> >>>> It's checking if a single gfn is private. >>>> >>> >>> But with huge page support we'd need to check a range of gfns... I guess >>> there's the argument of not keeping complexity for the future, but in >>> this case it's undoing functionality for this series and probably adding >>> it back later. >> >> let's leave the work for huge page support in the future. > > It's not just for hugepage support, the core functionality is used in this series > by __kvm_gmem_set_attributes() in: > > KVM: guest_memfd: Return early if range already has requested attributes > >>>> We can just use kvm_mem_is_private()? And it seems can be a separate patch. >>>> >>> >>> Do you mean that this refactoring could be a separate patch? I could >>> refactor out kvm_range_is_private() in a separate patch, then put in the >>> mt_for_each() check in this patch together as part of all the rest of >>> the "wiring". >>> >>> I considered that but it seemed like the refactoring was too small to >>> separate out into another patch when the mt_for_each() part is going to >>> be in this patch anyway. >>> >>> Or, I could add an earlier patch to first replace the call to >>> kvm_range_has_vm_memory_attributes() with a call to check just 1 gfn, >>> then this wiring patch would be simpler. >>> >> >> This is what I meant. An earlier patch to just replace >> kvm_range_has_vm_memory_attributes() with kvm_mem_is_private(). Then we can >> drop this 'big' diff in this patch. >> >> If kvm_range_is_private() is useful/required by huge page support, then let >> the huge page series to introduce it. It has nothing to do with the in-place >> conversion series. > > If it weren't for the fact that the range-based search is used later in this > series, I would 100% agree with Xiaoyao. > But since the core logic is used and needed elsewhere, I don't see it a problem. Without introducing kvm_range_is_private() in this patch, the core logic of range-based search on gmem can still be introduced as kvm_gmem_range_has_attributes() directly in patch 10 or in a separate patch. > and because kvm_range_has_vm_memory_attributes() takes a range,> my vote is to provide the plumbing now, even though a small portion of it isn't > strictly necessary. So my initial feedback was "we can just use kvm_mem_is_private(kvm, gfn)". It makes code simpler. And as a bonus, the logic to choose between gmem-based attribute query and vm-based attribute query is hidden from the static call. The second bonus of dropping kvm_range_is_private() is that we can eliminate one more chunk in patch 20.