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AFNElJ+P7lnYGEck6cPXiZVfNs9IaB4BQtVg5eAAgaTanTw6AigsS4dvsNHb0n7+w4/8m5wrsGU2WCVsow==@kvack.org X-Gm-Message-State: AOJu0YwKDfp5/FTymxS7ZXytvMbGKdQgugBygRjWdtf05ShnvfjOPoEf +g2voNSowCdcUn2zrK5uwZncIXDv6G0pRX9NrrHX3Z3ZjACwRVh2zHJkyqfbBz12dApsGzCyK6V fLw3Z7A== X-Received: from pgbck12.prod.google.com ([2002:a05:6a02:90c:b0:c8a:b173:5516]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a20:d045:b0:3b4:904f:c9cd with SMTP id adf61e73a8af0-3bc5181907emr14837899637.6.1782177766311; Mon, 22 Jun 2026 18:22:46 -0700 (PDT) Date: Mon, 22 Jun 2026 18:22:45 -0700 In-Reply-To: Mime-Version: 1.0 References: <20260618-gmem-inplace-conversion-v8-0-9d2959357853@google.com> <20260618-gmem-inplace-conversion-v8-23-9d2959357853@google.com> Message-ID: Subject: Re: [PATCH v8 23/46] KVM: TDX: Make source page optional for KVM_TDX_INIT_MEM_REGION From: Sean Christopherson To: Yan Zhao Cc: ackerleytng@google.com, 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, 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 , 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-Rspam-User: X-Stat-Signature: pn9ebwjkmquwd6a874q7uajdhwt4wg9m X-Rspamd-Queue-Id: 221D318000A X-Rspamd-Server: rspam06 X-HE-Tag: 1782177767-8677 X-HE-Meta: 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 LVRHgrIA 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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 Mon, Jun 22, 2026, Yan Zhao wrote: > On Thu, Jun 18, 2026 at 05:32:00PM -0700, Ackerley Tng via B4 Relay wrote: > > From: Ackerley Tng > > > > Update tdx_gmem_post_populate() to handle cases where a source page is > > not explicitly provided. Instead of returning -EOPNOTSUPP when src_page > > is NULL, default to using the page associated with the destination PFN. > > > > This change allows for in-place memory conversion where the data is > > already present in the target PFN, ensuring the TDX module has a valid > > source page reference for the TDH.MEM.PAGE.ADD operation. > > > > Signed-off-by: Ackerley Tng > > Signed-off-by: Sean Christopherson > > --- > > Documentation/virt/kvm/x86/intel-tdx.rst | 4 ++++ > > arch/x86/kvm/vmx/tdx.c | 11 ++++++++--- > > 2 files changed, 12 insertions(+), 3 deletions(-) > > > > diff --git a/Documentation/virt/kvm/x86/intel-tdx.rst b/Documentation/virt/kvm/x86/intel-tdx.rst > > index 6a222e9d09541..74357fe87f9ec 100644 > > --- a/Documentation/virt/kvm/x86/intel-tdx.rst > > +++ b/Documentation/virt/kvm/x86/intel-tdx.rst > > @@ -158,6 +158,10 @@ KVM_TDX_INIT_MEM_REGION > > Initialize @nr_pages TDX guest private memory starting from @gpa with userspace > > provided data from @source_addr. @source_addr must be PAGE_SIZE-aligned. > > > > +If guest_memfd in-place conversion is enabled, pass NULL for @source_addr to > > +initialize the memory region using memory contents already populated in > > +guest_memfd memory. > > + > > Note, before calling this sub command, memory attribute of the range > > [gpa, gpa + nr_pages] needs to be private. Userspace can use > > KVM_SET_MEMORY_ATTRIBUTES to set the attribute. > > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c > > index ffe9d0db58c59..56d10333c61a7 100644 > > --- a/arch/x86/kvm/vmx/tdx.c > > +++ b/arch/x86/kvm/vmx/tdx.c > > @@ -3198,8 +3198,12 @@ static int tdx_gmem_post_populate(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn, > > if (KVM_BUG_ON(kvm_tdx->page_add_src, kvm)) > > return -EIO; > > > > - if (!src_page) > > - return -EOPNOTSUPP; > > + if (!src_page) { > > + if (!gmem_in_place_conversion) > When userspace turns on gmem_in_place_conversion while creating guest_memfd > without the MMAP flag, the absence of src_page should still be treated as an > error. Why MMAP? Shouldn't this be a general "if (!src_page && !up-to-date)"? Just because userspace _can_ mmap() the memory doesn't mean userspace _has_ mmap()'d and written memory. And when write() lands, MMAP wouldn't be necessary to initialize the memory. > Additionally, to properly enable in-place copying for the TDX initial memory > region, userspace must not only specify source_addr to NULL, but also follow > a specific sequence (where steps 1/2/3/7 are required only for in-place copy): > 1. create guest_memfd with MMAP flag > 2. mmap the guest_memfd. > 3. convert the initial memory range to shared. > 4. copy initial content to the source page. > 5. convert the initial memory range to private > 6. invoke ioctl KVM_TDX_INIT_MEM_REGION. > 7. do not unmap the source backend. > > So, would it be reasonable to introduce a dedicated flag that allows userspace > to explicitly opt into the in-place copy functionality? e.g., Why? It's userspace's responsibility to get the above right. If userspace fails to provide a src_page when it doesn't want in-place copy, that's a userspace bug.