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AFNElJ8Y7X3cCF/oyh3K7+JTBXThk6RLmAyOPblU2wgVmtOENLG5daztd6J2x6fbvo3OM5PNg+wT2910SA==@kvack.org X-Gm-Message-State: AOJu0YwoixSG2PFHMJXreU1SvyXeBzfxd+WChZ0/dQYbUMvPfYOLERGX e8iCUiSOWwppMUZqaxZ1AA+Wckilfh5x2ppiwYDLeO49ZFiTmPrxrXYtara0JO0yr7gP0Z/3/4x 3C1EbFw== X-Received: from pgc20.prod.google.com ([2002:a05:6a02:2f94:b0:c82:2d72:ac91]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a21:9186:b0:39f:3559:750d with SMTP id adf61e73a8af0-3b40fd77806mr3582072637.31.1780063062497; Fri, 29 May 2026 06:57:42 -0700 (PDT) Date: Fri, 29 May 2026 06:57:41 -0700 In-Reply-To: <9huzwlwnbgdd.fsf@tarunix.c.googlers.com> Mime-Version: 1.0 References: <9huzwlwnbgdd.fsf@tarunix.c.googlers.com> Message-ID: Subject: Re: [RFC PATCH v1 0/8] liveupdate: kvm: Guest_memfd preservation From: Sean Christopherson To: tarunsahu@google.com Cc: axelrasmussen@google.com, mark.rutland@arm.com, skhawaja@google.com, Mike Rapoport , sagis@google.com, Jason Gunthorpe , Shuah Khan , ackerleytng@google.com, corbet@lwn.net, dmatlack@google.com, Paolo Bonzini , Andrew Morton , vannapurve@google.com, Pratyush Yadav , david@redhat.com, aneesh.kumar@kernel.org, vipinsh@google.com, Alexander Graf , David Hildenbrand , Pasha Tatashin , linux-kernel@vger.kernel.org, linux-mm@kvack.org, kexec@lists.infradead.org, linux-kselftest@vger.kernel.org, kvm@vger.kernel.org Content-Type: text/plain; charset="us-ascii" X-Rspam-User: X-Rspamd-Queue-Id: 36BCDC0012 X-Rspamd-Server: rspam03 X-Stat-Signature: t77arqitr4ygi4aoxrqqam6fnpeuphja X-HE-Tag: 1780063063-166748 X-HE-Meta: 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 Mh/Tqpb2 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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 Thu, May 28, 2026, tarunsahu@google.com wrote: > 3. No need to preserve kvm->mem_attr_array, as this is on deprecating > path and For this series, where only fully shared guest_memfd is > supported for liveupdate, preservation of these attributes not > required. > > Due to time constraints: > we have one open Question left: > 1. How to check guest_memfd is fully shared. Currently that is being > done by INIT_SHARED flag. But with in-place it is going to change > its meaning and it will mean only durng the creation of guest_memfd > it is shared whose folios can be converted to private. > So for this series, I am looking for suggestion, what is the best way > to find the sharedness of guest_memfd which will be compatible with > in-place series. OR we can go like this (my personnel recommendation): > > if (guest_memfd_is_fully_shared()) > return true; // support the preservation > > // This series > int guest_memfd_is_fully_shared(void) { > if (guest_memfd->flags & GUEST_MEMFD_FLAG_INIT_SHARED) > return true; > return false; > } > > TO:: > // Once in-place conversion series lands. > int guest_memfd_is_fully_shared(void) { > if (No Private flags in (guest_memfd->attributes)) > return true; > return false; > } Given that lack of support isn't going to be limited to _just_ guest_memfd, simply disallow preservation if the VM supports private memory: if (kvm_arch_has_private_mem(kvm)) return -EOPNOTSUPP;