From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.zytor.com (terminus.zytor.com [198.137.202.136]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8B057155322; Mon, 13 Oct 2025 19:45:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.136 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760384732; cv=none; b=Jq906uWRlV1kYCTZMLp9whEtTSPKSRV5RAWzvvy7Y91piPv9gugTXYIVUHq2m6825QoklcbCTk+IujbcCC7mwnGcwoaQ4gZfKoRd6jQ6RqU0ViJufb/NwKTCNwuPFnEqk5GPDIfooRIEYVZ0eZEy6hZwoGbx8M6Dg8UsRLwaUOk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760384732; c=relaxed/simple; bh=MY+YRUQKLtJYZJyEq96fgMk0w7vwxMzr5S0vyCUFB6Y=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=j0OcLAPG7lrlnfw6TFJWqNv4JE0CMFCH1dXwmiVzNmvRFQKpCycCYJNxneeEJRU37itw6Elz/DRirdbmc1i2Qunwv9ViP6b3XaEw4/V+fS3N+O+641T1cxJw1eWqD6GCwFYLeUG9Bz+8u4EaNm79nG1i504TmujJ1G9BNuLzbIw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com; spf=pass smtp.mailfrom=zytor.com; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b=OIcplRen; arc=none smtp.client-ip=198.137.202.136 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=zytor.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b="OIcplRen" Received: from [IPV6:2601:646:8081:9484:201e:bc0f:a7c6:ca8d] ([IPv6:2601:646:8081:9484:201e:bc0f:a7c6:ca8d]) (authenticated bits=0) by mail.zytor.com (8.18.1/8.17.1) with ESMTPSA id 59DJiSUF1442566 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NO); Mon, 13 Oct 2025 12:44:32 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 59DJiSUF1442566 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2025092201; t=1760384682; bh=1aJOeaPPB1LUMhLyvXF0SOu3n0ovMqgDmMOTUIZYXXs=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=OIcplRenwsuEFxrQG/i7vbTNL5ee01maFltEu/9+zMjTrqySBAieZqr/Jnicpqoey b2HHI6yIRprdPUAGYIWjF/kEanvHHWXiC6nPSVA5IqK35TSVZ+7IrLFGmq98r1j8DZ V5aeeP4aUdWPcHl9xR2EvzbOu0Jiq4U5iHSVyec1uPZV1rwgNuPSY0NPtjes+43aIl K+H3VHnCes599MCCY8JoDUtC3q84PpJfE6CcvcH+f08aBA9dJ3t2a/zXK+rcx8az32 UvQcHsa4qPbKZ9DC6gaWyDpFxKVkpNfFVN7H2GKOXZ8fif9gO0qQ83SQs1WuiyNyu6 EQ1aEfan++sog== Message-ID: <494caf29-8755-4bc6-a2c3-b9d0b3e9b78d@zytor.com> Date: Mon, 13 Oct 2025 12:44:19 -0700 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] vdso: Remove struct getcpu_cache To: Andy Lutomirski , Dave Hansen Cc: =?UTF-8?Q?Thomas_Wei=C3=9Fschuh?= , Huacai Chen , WANG Xuerui , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, Richard Weinberger , Anton Ivanov , Johannes Berg , Vincenzo Frascino , Shuah Khan , loongarch@lists.linux.dev, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, linux-um@lists.infradead.org, linux-api@vger.kernel.org, linux-kselftest@vger.kernel.org References: <20251013-getcpu_cache-v2-1-880fbfa3b7cc@linutronix.de> Content-Language: en-US, sv-SE From: "H. Peter Anvin" In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 2025-10-13 10:14, Andy Lutomirski wrote: > > I don't actually remember whether the kernel ever used this. It's > possible that there are ancient kernels where passing a wild, non-null > pointer would blow up. But it's certainly safe to pass null, and it's > certainly safe for the kernel to ignore the parameter. > One could imagine an architecture which would have to execute an actual system call wanting to use this, but on x86 it is pointless -- even the LSL trick is much faster than a system call, and once you account for whatever hassle you would have to deal with do make the cache make sense (probably having a global generation number and/or a timestamp to expire it) it well and truly makes no sense. -hpa