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AJvYcCWb06PAeR30zXskuXUL2GvoMbcBJlO97iAo+lhUw5hXHOrhXcQJ9sluvEFHMxyh2hImpKkp+lpuVw==@kvack.org X-Gm-Message-State: AOJu0YyctQ9X0lvdQ6LxSKcww+AzzmK/Tzu6LszSxxEKRutfSxBBI10F 1rIugtCalMyqJuABM3hgDoV3UojOyLyhu5zkkWv9LajTAdbS1cxn1N2vdtU6QJ7/i+Kbiwe7U+l YXLcnB144IBt4RH/HRU/7PwlQ6+kA+cF5T/nfPWks X-Gm-Gg: ASbGnctc2niwNfW7SKkbSYBypEDXpJJNvibPw8YObTxrFvACVKTAxi5065l/FpWvuSu xh2JZ+jUhQjPcH0PuoYPPP6ZEPJdCkYZkN3KYKX/Ga1z9zFNRPjKlpsm7YC8vL6qkviTbrk/Gzc ITgZbLBz/oAamZ0AS9QLBqvAJPbEp/V6AsrG/QM1pbZ+0JNADmhBj4V+KbuFHHQgQY4VR9E2XFL 9SiGCLqN+OkNj8x5ZZNN2NrRk8B2Z6+tFvJ1z2aKCsRloeczTkHpIPfx1VoSFPYper5+XY= X-Google-Smtp-Source: AGHT+IHpaQt5+0pcMaIPZPH6gSZTkFVrpAwY4H8c4baBjFBSVkthH7idSXvBuMd/bzOIGy2JEPxjML5/b0vPbAuuafA= X-Received: by 2002:a05:6102:18d7:b0:596:9fd8:9268 with SMTP id ada2fe7eead31-5db7e0ae09amr369527137.8.1761606310932; Mon, 27 Oct 2025 16:05:10 -0700 (PDT) MIME-Version: 1.0 References: <20251021000852.2924827-1-pasha.tatashin@soleen.com> <20251021000852.2924827-4-pasha.tatashin@soleen.com> In-Reply-To: <20251021000852.2924827-4-pasha.tatashin@soleen.com> From: David Matlack Date: Mon, 27 Oct 2025 16:04:42 -0700 X-Gm-Features: AWmQ_bkP7kzVj43hv33PyztzJtnw3ebpuh-wFqU7ylSkamn2ND777xZJOuB-IiQ Message-ID: Subject: Re: [PATCH v3 3/3] liveupdate: kho: allocate metadata directly from the buddy allocator To: Pasha Tatashin Cc: akpm@linux-foundation.org, brauner@kernel.org, corbet@lwn.net, graf@amazon.com, jgg@ziepe.ca, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, masahiroy@kernel.org, ojeda@kernel.org, pratyush@kernel.org, rdunlap@infradead.org, rppt@kernel.org, tj@kernel.org, jasonmiu@google.com, skhawaja@google.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: 14mskx91w1pyzwqdwoja7ny3uguojhkj X-Rspamd-Queue-Id: 3AB7540004 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1761606312-502902 X-HE-Meta: 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 Y83oMqWc ArS/Hu+DscQ9fx4QnnLCQbWmxyq1/ZHS0CS6/mrttuJwSG+GgAeOcqAOCy79UShM27Ewccx0qCh9vEM+jpkhCo+I9Z93CvO78Bq6L8fkvhJaVM9HdiNkMEeSjR4yB2JZ9JqpJ2zwwUd/t7ak/ESOulTS4FwUvjkrXVH1nkz4XYuRaeYamdevwOt+4hAl8HjgQI4S70cKAw7JL2dV5aFgutaa77I2iSHEPV/W5lgEkdeNfzqVHsUE1wvi5aL5BQoabvQvEHp7605PzJzWeW34oSMz0vaGW03lFWsd/f63llbIjDZY= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Oct 20, 2025 at 5:09=E2=80=AFPM Pasha Tatashin wrote: > > KHO allocates metadata for its preserved memory map using the slab > allocator via kzalloc(). This metadata is temporary and is used by the > next kernel during early boot to find preserved memory. > > A problem arises when KFENCE is enabled. kzalloc() calls can be > randomly intercepted by kfence_alloc(), which services the allocation > from a dedicated KFENCE memory pool. This pool is allocated early in > boot via memblock. > > When booting via KHO, the memblock allocator is restricted to a "scratch > area", forcing the KFENCE pool to be allocated within it. This creates a > conflict, as the scratch area is expected to be ephemeral and > overwriteable by a subsequent kexec. If KHO metadata is placed in this > KFENCE pool, it leads to memory corruption when the next kernel is > loaded. > > To fix this, modify KHO to allocate its metadata directly from the buddy > allocator instead of slab. > > Fixes: fc33e4b44b27 ("kexec: enable KHO support for memory preservation") > Signed-off-by: Pasha Tatashin > Reviewed-by: Pratyush Yadav Reviewed-by: David Matlack