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AFNElJ/JhNJO3cIfKuPLLcdUHjwfHirDZsnjga6IuAyyR8OuJpArRRldh3bYM7lj1tx6S5p9+vwL6ZwwPw==@kvack.org X-Gm-Message-State: AOJu0YxMVHvXslLsdeygiBonf0CIwEj7ai+DitheCPM2GH/bGR1v/HTp 5I7JdARsY8oV1w5TNaRhb9nM18wnuowN1Tp/dTVZ5H5QB7J2z2zdos6i2PCNZThAb7s8d4ZQplF F1xv2ww== X-Received: from pllk9.prod.google.com ([2002:a17:902:7609:b0:2b4:5bcc:fc4a]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:903:1246:b0:2bc:90b6:3e6f with SMTP id d9443c01a7336-2beb0347191mr37692105ad.4.1779455338970; Fri, 22 May 2026 06:08:58 -0700 (PDT) Date: Fri, 22 May 2026 06:08:58 -0700 In-Reply-To: Mime-Version: 1.0 References: <20260507-gmem-inplace-conversion-v6-0-91ab5a8b19a4@google.com> <20260507-gmem-inplace-conversion-v6-21-91ab5a8b19a4@google.com> Message-ID: Subject: Re: [PATCH v6 21/43] KVM: SEV: Make 'uaddr' parameter optional for KVM_SEV_SNP_LAUNCH_UPDATE 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-Rspam-User: X-Rspamd-Queue-Id: B89EB140014 X-Rspamd-Server: rspam03 X-Stat-Signature: bh3ew1rym3bbgusfn3yrzqjnmupjnxuf X-HE-Tag: 1779455340-370854 X-HE-Meta: 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 ZE0WmJxt 4MbhTbge6Rcn/tf2htQsuJcQcI1YC2c5RDRO0jFVZOTEa0UyBZ8e+OS3bXPOjfbbs0kOWUrL+d9z5SsRKDG+tECGycBm59RzeVCmUveSX1TmLybNpap7LUReYUU4oO7157ffdvpwt6oeyRLnEDxpeVQdkdmRA2ALWtjfYRbh/0GiTC94eFB7axX0e5Fvkro3/ebV5/1u4KOpSw7tPMLn8LUTORQaHfa6QNXdNHqtUDC3doF6hziFk29cyFp4WKZnlGt5CuWv4F8rdf4E5Ts4acVMyHGIbpJKTW71VBqWJgN0dQL8sQuo2khSWr+3TAVSUKJuiUOjeayJ0fB0V2+WUmGxKWLABAVuA3460s7aVZlDMucmk21Pspr9a1vBkpwzZl7khvWlJj1QIj1S6l9njvRRmXVT6aFiwz7qAawMoYfS+81VCU8HOfBKg55B6T0AtIiIJ6Du0Jobwl2vsyXm8TDHRT/W7uWboV5AxC0JuabDFBMZ7baf0GTjDUjNKpzZeLFi72PWdnAFYxpdwTCAED/5eil5RD12aDDas+F1yg2mzWmgE8so1eD5W6hOCJraKR2ov20dN0vdsFU6Glqiw2+GthwTSBw3iTpkxV63FhUxckvrbETNrR1wC0QilWrS7AQt6WbkjsIX/TgTvYnC2WQAII2tV9qOhW0/wS5KsZkeIXouVts9+LZoHwfEVBdQwJJvG9ewDRXzcklQK65TFSciOpg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, May 21, 2026, Ackerley Tng wrote: > Sean Christopherson writes: > > > On Thu, May 21, 2026, Fuad Tabba wrote: > >> Hi, > >> > >> On Thu, 7 May 2026 at 21:22, Ackerley Tng via B4 Relay > > diff --git include/linux/kvm_host.h include/linux/kvm_host.h > > index 61a3430957f2..b83cda2870ba 100644 > > --- include/linux/kvm_host.h > > +++ include/linux/kvm_host.h > > @@ -2596,7 +2596,8 @@ int kvm_arch_gmem_prepare(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn, int max_ord > > typedef int (*kvm_gmem_populate_cb)(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn, > > struct page *page, void *opaque); > > > > -long kvm_gmem_populate(struct kvm *kvm, gfn_t gfn, void __user *src, long npages, > > +long kvm_gmem_populate(struct kvm *kvm, gfn_t start_gfn, void __user *src, > > + long npages, bool writable, > > What do you think of need_writable_src instead of just writable for the > variable name? How about "may_write_src" or "may_writeback_src"? > > kvm_gmem_populate_cb post_populate, void *opaque); > > #endif > > > > diff --git virt/kvm/guest_memfd.c virt/kvm/guest_memfd.c > > index a35a55571a2d..6553d4e032ce 100644 > > --- virt/kvm/guest_memfd.c > > +++ virt/kvm/guest_memfd.c > > @@ -858,7 +858,8 @@ static long __kvm_gmem_populate(struct kvm *kvm, struct kvm_memory_slot *slot, > > return ret; > > } > > > > -long kvm_gmem_populate(struct kvm *kvm, gfn_t start_gfn, void __user *src, long npages, > > +long kvm_gmem_populate(struct kvm *kvm, gfn_t start_gfn, void __user *src, > > + long npages, bool writable, > > kvm_gmem_populate_cb post_populate, void *opaque) > > { > > struct kvm_memory_slot *slot; > > @@ -892,8 +893,9 @@ long kvm_gmem_populate(struct kvm *kvm, gfn_t start_gfn, void __user *src, long > > > > if (src) { > > unsigned long uaddr = (unsigned long)src + i * PAGE_SIZE; > > + unsigned int flags = writable ? FOLL_WRITE : 0; > > How about using FOLL_WRITE | FOLL_NOFAULT so if it weren't writable to > start with, don't CoW, just error out? Eh, I don't see any value in value in erroring out if userspace is doing something unusual. If breaking CoW was actually problematic somehow, then sure. But AFAICT it's overall harmless. > Like you said above the CPUID page provided as src_page would have been > written to before, so it should have been mapped as writable.