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[80.230.47.179]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48a82301ad1sm642932375e9.9.2026.05.05.08.41.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 05 May 2026 08:41:22 -0700 (PDT) Date: Tue, 5 May 2026 11:41:20 -0400 From: "Michael S. Tsirkin" To: alexanderduyck@fb.com, virtio-comment@lists.linux.dev Subject: virtio balloon poison feature Message-ID: <20260505102918-mutt-send-email-mst@kernel.org> Precedence: bulk X-Mailing-List: virtio-comment@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: kJ3WvRglc1susNhky4EI0qiLTYi85e13zFpC04EeEf4_1777995684 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Hi Alexander, all. I am looking at this old commit and I am confused: commit 4749f03e72f8ff6e66f54e38e41a560014e1a0e3 Author: Alexander Duyck Date: Tue Aug 25 07:45:10 2020 -0700 content: Document balloon feature page poison Page poison provides a way for the guest to notify the host that it is initializing or poisoning freed pages with some specific poison value. As a result of this we can infer a couple traits about the guest: 1. Free pages will contain a specific pattern within the guest. 2. Modifying free pages from this value may cause an error in the guest. 3. Pages will be immediately written to by the driver when deflated. There are currently no existing features that make use of this data. In the upcoming feature free page reporting we will need to make use of this to identify if we can evict pages from the guest without causing data corruption. Add documentation for the page poison feature describing the basic functionality and requirements. Fixes: https://github.com/oasis-tcs/virtio-spec/issues/84 Reviewed-by: Cornelia Huck Reviewed-by: David Hildenbrand Signed-off-by: Alexander Duyck Signed-off-by: Cornelia Huck here is what I do not understand: why does driver tell device that it will poison the pages after deflate? device does not access them anymore so why does it care? should this have been *before inflate*, actually? how was this envisioned to be used? Thanks, -- MST