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a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1791785643; bh=uVnR4MPE16Rgbszkf4sDlKvI9WzIxticvq1LhqhOaX4=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=SSJvN2blVpRzvYTZwQHl5g3Tcxsa0FG0knR65KyNLoDmt2rD7Y37wengoRMOfkped oRs5yVYH3eH1c4HYDc2ioq/IMvzt7IRQBVOB+c/tl/PqHdbxtnHsgi+iXwI127ylAk ZCjPk+4I8kZyX1SIVa+qYM/NVYLcN0lIxQ4XjUaY= Message-ID: Date: Mon, 12 Oct 2026 11:43:58 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] selftests/mm: fix uffd move-pmd test crash on 64K base page systems To: Zenghui Yu , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: akpm@linux-foundation.org, rppt@kernel.org, peterx@redhat.com, david@kernel.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, surenb@google.com, mhocko@suse.com References: <20261011163527.95988-1-zenghui.yu@linux.dev> Content-Language: en-US From: Sarthak Sharma In-Reply-To: <20261011163527.95988-1-zenghui.yu@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: b4uxmys85mmg3qdwx1weu74kngyka4jf X-Rspamd-Queue-Id: 06C9420009 X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1791785644-786973 X-HE-Meta: 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 +tYjg/FA C2g74q4piTCUr5H4bhJQcbcEi2AdcEILXyc9BI/Jz1MqnJdi7A/tiXwxvPMSHEInKUDDsjggr8aY2dwahzdhG4Ccgh655ztTCXdstEP7ZSZIPTvbUbNE3evJgtjnPrRXvojC3K52at//0NFK9yjbHCd9dciv2RDi6+htx7/Uhw/WlhxTe93rx9xSrcE1F4deVRZm3GJkS02laRtFBpFI5xNllzOQgXN4ZF2HIy5S9Rl+heVH900pUMeiQW5T2/Unoha+jNUQIIXYg5LAEayZmbGdbDpmtpxMoy42wNhGfr+4UjU2UnjrVIBIakSK5hpbqh3X2yQZf41n4yzl1jqTW9ObJUmZRozxcctrv Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Zenghui! On 10/11/26 10:05 PM, Zenghui Yu wrote: > From: "Zenghui Yu (Huawei)" > > uffd_move_pmd_test()/uffd_move_test_common() splits the test area into > chunks of chunk_size and moves them one by one. On arm64 with 64K base > pages the chunk_size (read_pmd_pagesize()) is 512MB, which is larger than > the whole 32MB (UFFD_TEST_MEM_SIZE) test area: > > step_count = nr_pages / (chunk_size / page_size) == 0 > > Because chunk_size > page_size, the test then aligns both areas up to > 512MB, which points far outside of the 32MB mappings, and decrements > step_count, which underflows to ULONG_MAX. The verification loop then > runs away and the first dereference of area_src faults with a SIGSEGV. > > Skip the test when a single chunk cannot fit into the test area. > > Fixes: a2bf6a9ca805 ("selftests/mm: add UFFDIO_MOVE ioctl test") > Signed-off-by: Zenghui Yu (Huawei) > --- I run the test on a 64k kernel. Before the patch, a segmentation fault occurred, which was fixed by the patch. So: Tested-by: Sarthak Sharma Though Sashiko has a few nits [1] you might take a look at. [1] https://sashiko.dev/#/patchset/20261011163527.95988-1-zenghui.yu%40linux.dev