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Wed, 23 Sep 2026 06:00:34 -0700 (PDT) Received: from ziepe.ca ([130.41.10.202]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-33e96358e2bsm6859478eec.16.2026.09.23.06.00.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 23 Sep 2026 06:00:33 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1x9MaO-0000000DYPQ-01dr; Wed, 23 Sep 2026 10:00:32 -0300 Date: Wed, 23 Sep 2026 10:00:31 -0300 From: Jason Gunthorpe To: Catalin Marinas Cc: "Aneesh Kumar K.V" , linux-coco@lists.linux.dev, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, iommu@lists.linux.dev, Andrew Morton , christian.koenig@amd.com, Joerg Roedel , Marc Zyngier , Marek Szyprowski , Robin Murphy , Steven Price , Sumit Semwal , Suzuki K Poulose , Thomas Gleixner , Will Deacon , dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, linux-media@vger.kernel.org, linux-mm@kvack.org Subject: Re: [RFC PATCH v7 02/13] mm: Add an allocator for CoCo shared memory Message-ID: <20260923130031.GE1540250@ziepe.ca> References: <20260921144847.501151-1-aneesh.kumar@kernel.org> <20260921144847.501151-3-aneesh.kumar@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: jnpristki3e9o6ecndyij9hfyrgosku7 X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 51C8E80005 X-HE-Tag: 1790168438-264845 X-HE-Meta: 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 XpJdjm6N wLhiVIkLTugV3pjmSFEeryBXvG6/mom1Z80vgUbmepFqz0o+1Ty8aOmxED71RSXH94SOu+rmrBrg4z7NTsQjcIDARy0H3lT4dMsLanzEsb9TbCkkCWZq8RVOihSFPRjgbufVxIgZ5Y970NdlDDY3odEMCKukneoa6XOHD9VvaUAKtbs3ki3fAqqe6Md65dcpP0G8JghHnOg94BCwTNxlBuo8LnXvxs4y8qEeCZth0R4k8PD9SBtVmnB+cqfRoF7nF6KOAUwrunwekConpLWXWQzCztggNAkXvk9gqDaWnDCKnEdBZGxtrTH9G3A== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Sep 23, 2026 at 10:42:39AM +0100, Catalin Marinas wrote: > On pKVM, we want set_memory_decrypted() to zero the buffer > before the host can access it (I guess currently relying on __GFP_ZERO > allocations). Since no cryptographic encryption takes place, there's not > much point in memset'ing again after the operation as the content was > already zeroed. It sounds like this a pkvm unique thing, since RMM always makes the memory hidden, pkvm flow should do it too. Either inside its guest set_memory_decrypted() or inside the hypervisor like RMM. Hypervisor doing it is the right place, hypervisor always needs to ensure guest memory is cleansed whenever the guest gives it up. Either via a private to shared, unmap or just exiting. > I don't think cc_make_shared() has the right information on how to > safely and efficiently do the zeroing. That's only known to the > set_memory_* backend. So you'd have to propagate the flag down. +1 Jason