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Wed, 04 Nov 2026 12:42:39 -0800 (PST) Received: from nobara ([83.231.69.9]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48fecac1a1csm5716451f8f.12.2026.11.04.12.42.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Nov 2026 12:42:39 -0800 (PST) From: "Jose A. Perez de Azpillaga" To: Mike Rapoport , Andrew Morton , Kees Cook , Changyuan Lyu , Alexander Graf Cc: Tony Luck , "Guilherme G. Piccoli" , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Pratyush Yadav , Pasha Tatashin , kexec@lists.infradead.org, "Jose A. Perez de Azpillaga" Subject: [PATCH v2] memblock: don't allocate new reserve_mem regions on a KHO boot Date: Wed, 4 Nov 2026 21:42:17 +0100 Message-ID: <20261104204235.9066-1-azpijr@gmail.com> X-Mailer: git-send-email 2.56.0 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On a KHO boot, a reserve_mem region that can't be revived is allocated from KHO_NOPRSRV memory, which includes the bootmem the next kernel boots out of. With CONFIG_KEXEC_HANDOVER_DEBUG, preserving the region then fails: WARNING: kernel/liveupdate/kexec_handover.c:1245 at kho_preserve_pages+0x168/0x180 failed to prepare memblock FDT for KHO: -22 Without it, the next kernel puts its memmap on top of the region and the ramoops records in it are lost. There is no use case for adding regions across a live update, so fail instead of allocating, and drop the TODO. Fixes: f99230780211 ("memblock: add KHO support for reserve_mem") Signed-off-by: Jose A. Perez de Azpillaga --- Changes in v2: - fail on a KHO boot instead of allocating outside bootmem, as agreed with Pratyush [1]. this drops v1's patch 1. - not an RFC anymore. - based on v7.4-rc1. v1: https://lore.kernel.org/all/20261021211058.83483-3-azpijr@gmail.com/ [1] https://lore.kernel.org/all/2vxzfqxglrg6.fsf@kernel.org/ mm/memblock.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/mm/memblock.c b/mm/memblock.c index a450092a80fb..e325e0542c9a 100644 --- a/mm/memblock.c +++ b/mm/memblock.c @@ -2827,7 +2827,16 @@ static int __init reserve_mem(char *p) if (reserve_mem_kho_revive(name, size, align)) return 1; - /* TODO: Allocation must be outside of KHO_NOPRSRV region */ + /* + * On a KHO boot memblock only allocates from KHO_NOPRSRV memory here, + * which includes the bootmem the next kernel boots out of. Only regions + * handed over by the previous kernel are supported. + */ + if (is_kho_boot()) { + pr_err("reserve_mem: can't allocate \"%s\" on a KHO boot\n", name); + return -EOPNOTSUPP; + } + start = memblock_phys_alloc(size, align); if (!start) { pr_err("reserve_mem: memblock allocation failed\n"); base-commit: 6628e7d4c6b25c8d18f1345e3a20d21829aae7e4 -- 2.56.0