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AJvYcCUUd4plwjJqsFZIyMw4+ZsmY/wt5P8TrGX4mYFVQ3Idy52ekeKLS/kRZ8roLRu+7rGepufRHUHmqQ==@kvack.org X-Gm-Message-State: AOJu0Yygq3zruxVjxcxIYXbrp4pFpMIY/hE0/pedlXwWUqNtTmq4/6Jd usyOvZWvjY0cWMsugOuHo/it2PABI9KWp9v5kFDdFip51/vmABv/yLpnLT0b5Dq43dvNufc9ATT XRvcdxRA7YaHRoq4wlkfFEtIOTaRxsHg9BCA+a0VAeg== X-Gm-Gg: ASbGncswLgu1fHNJmiSWk8+HWOHisiseFtZVC/q3o0lzKLjnwg/c705U5JSR9AX7L2H 6u2B545OlfZ4Av9xEpwa8lQlfHw857bApL3cOfuYCow7dGCBFwdQIQePMFelfyvhrtr/sg3TwO3 6bACiapJGw7cnbmq8HpHfNaNtYmcQDBKGBf1O5qhuFVthYRINWHre0LBBAsreBw4ci6kXDXClOy sdTdcnr2y8Vtuu4OfnwgDuH9GHPK/2Buw== X-Google-Smtp-Source: AGHT+IFgvnWABvFp2YO4aybRqOy0KXXsuvYtzVtzjFu719w6HusoLk54zzREdfAYZlsXpNluTDl3s5anm94ec20FQEM= X-Received: by 2002:a05:6402:5244:b0:634:544b:a755 with SMTP id 4fb4d7f45d1cf-639d5c3294cmr29350078a12.19.1760537985003; Wed, 15 Oct 2025 07:19:45 -0700 (PDT) MIME-Version: 1.0 References: <20251015053121.3978358-1-pasha.tatashin@soleen.com> <20251015053121.3978358-3-pasha.tatashin@soleen.com> In-Reply-To: From: Pasha Tatashin Date: Wed, 15 Oct 2025 10:19:08 -0400 X-Gm-Features: AS18NWBj8W1b8VguIoFufUrvIsQUXiGHkQ32JE7FqsyGBasY6kmjvm5a_9MOZ2k Message-ID: Subject: Re: [PATCH 2/2] liveupdate: kho: allocate metadata directly from the buddy allocator To: Pratyush Yadav 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, rdunlap@infradead.org, rppt@kernel.org, tj@kernel.org, jasonmiu@google.com, dmatlack@google.com, skhawaja@google.com, glider@google.com, elver@google.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: o65quh6eujy9je1zddu46fqffkp3s4g4 X-Rspamd-Queue-Id: EC8E210000C X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1760537986-706630 X-HE-Meta: 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 TD2bdkpr R9DXFifo7w9/RpVhoT9JqlpkUgpXtn9q0WpRyAEPBhy97xVFkht2j+XbpybdpqKO43Tqsy7pxg2dMiHmLVZg4n0kp4Pl3sgqFszicuVd4p1ANoDMJ0ixj9hooa+XrQ6Mf/EkWBw3MlIo493uHpc1IGz8UkiCGNew6uzhuuRgEjyZu41gFzYoLRoS8I5t3emUiD0eDYsG6pBHryp31mdlqlrr9Yw== 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 Wed, Oct 15, 2025 at 9:05=E2=80=AFAM Pratyush Yadav wrote: > > +Cc Marco, Alexander > > On Wed, Oct 15 2025, Pasha Tatashin wrote: > > > KHO allocates metadata for its preserved memory map using the SLUB > > 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. > > At some point, we'd probably want to add support for preserving slab > objects using KHO. That wouldn't work if the objects can land in scratch > memory. Right now, the kfence pools are allocated right before KHO goes > out of scratch-only and memblock frees pages to buddy. If we do that, most likely we will add a GFP flag that goes with it, so the slab can use a special pool of pages that are preservable. Otherwise, we are going to be leaking memory from the old kernel in the unpreserved parts of the pages. If we do that, kfence can ignore allocations with that new preservable GFP flag. Pasha