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AHgh+RrPAed6+oUQvwJ2LLINNdQRVgZMTxW+YEuGfutkEPu/TPCcOfJdXxZUIxHDcTJ0q+OmJ1L2NxXrr7HZOVE=@vger.kernel.org X-Gm-Message-State: AOJu0YxiMpEUN8cx5ROGoD6ZNgPzcP0ShHBBiztf9enx6sfNHcANOrVz npTFtQuOY6Do93/eozYdFgklfBWGn1sZOgShtRLou1GE3zUQP2JzypceM07sLWi2fLpTUE0EQx7 4ah8TNo+EgqyWqvsTmg== X-Received: from ejczw12-n2.prod.google.com ([2002:a17:907:e00c:20b0:c19:71f5:ee20]) (user=tarunsahu job=prod-delivery.src-stubby-dispatcher) by 2002:a17:907:ea8b:b0:c16:126b:98b4 with SMTP id a640c23a62f3a-c2039c03283mr2125010166b.3.1786368035983; Mon, 10 Aug 2026 06:20:35 -0700 (PDT) Date: Mon, 10 Aug 2026 13:20:34 +0000 In-Reply-To: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260728121138.1103610-1-tarunsahu@google.com> <20260728121138.1103610-9-tarunsahu@google.com> Message-ID: <9huz1pc6863h.fsf@tarunix.c.googlers.com> Subject: Re: [PATCH v4 08/11] KVM: guest_memfd: Add support for preservation via LUO From: tarunsahu@google.com To: Ackerley Tng , fuad.tabba@linux.dev, Andrew Morton , seanjc@google.com, dmatlack@google.com, Shuah Khan , Jonathan Corbet , david@redhat.com, Pasha Tatashin , Pratyush Yadav , sagis@google.com, Paolo Bonzini , Mike Rapoport , Alexander Graf Cc: linux-kselftest@vger.kernel.org, andre.przywara@arm.com, michael.roth@amd.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, will@kernel.org, vannapurve@google.com, maz@kernel.org, fvdl@google.com, kvm@vger.kernel.org, oliver.upton@linux.dev, kvmarm@lists.linux.dev, alexandru.elisei@arm.com, skhawaja@google.com, aneesh.kumar@kernel.org, linux-doc@vger.kernel.org, David Hildenbrand , yan.y.zhao@intel.com, kexec@lists.infradead.org, suzuki.poulose@arm.com Content-Type: text/plain; charset="UTF-8" Ackerley Tng writes: > Tarun Sahu writes: > >> >> [...snip...] >> >> +static bool kvm_gmem_luo_can_preserve(struct liveupdate_file_handler *handler, struct file *file) >> +{ >> + struct inode *inode = file_inode(file); >> + struct gmem_file *gmem_file; >> + struct kvm *kvm; >> + >> + if (inode->i_sb->s_magic != GUEST_MEMFD_MAGIC) >> + return false; >> + >> + gmem_file = file->private_data; >> + if (!gmem_file) >> + return false; >> + >> + /* >> + * Only Fully-shared guest_memfd preservation is supported >> + */ >> + if (!(GMEM_I(inode)->flags & GUEST_MEMFD_FLAG_INIT_SHARED)) >> + return false; >> + > > The above check can probably be removed. I think the core thing about > this series is "we can preserve any memory that doesn't have any > encryption state that goes along with it", and so the check for > kvm_arch_has_private_mem() below would be sufficient to gate that. Sounds Good. Will remove it in next version. I will rephrase the Line: "Support only fully shared guest_memfd" => "Support only guest_memfd that does not support private pages and also can not be converted to private" > >> + /* >> + * It makes sure that no memory can be converted to private >> + * even if it was initially fully shared (in-place conversions are >> + * prevented). >> + */ >> + kvm = gmem_file->kvm; >> + if (kvm_arch_has_private_mem(kvm)) >> + return false; >> + > > For now, has_private_mem == has some encryption state that we can't > preserve yet. > > This also gates off KVM_X86_SW_PROTECTED_VM, but I guess that is > intended, since when work is done for preserving encryption state, we > can then test using KVM_X86_SW_PROTECTED_VM, and only then, remove this > check? Yes, It will be enabled when private memory preservation will be supported. > >> + if (mapping_large_folio_support(inode->i_mapping)) >> + return false; >> + >> + return true; >> +} >> + >> >> [...snip...] >>