From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9EB77C433EF for ; Wed, 4 May 2022 19:59:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234674AbiEDUCq (ORCPT ); Wed, 4 May 2022 16:02:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35586 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232611AbiEDUCl (ORCPT ); Wed, 4 May 2022 16:02:41 -0400 Received: from mail-il1-x130.google.com (mail-il1-x130.google.com [IPv6:2607:f8b0:4864:20::130]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D55204EDFB for ; Wed, 4 May 2022 12:58:47 -0700 (PDT) Received: by mail-il1-x130.google.com with SMTP id y16so1548614ilc.7 for ; Wed, 04 May 2022 12:58:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=GsfXoNKONKDKWhJHjg7OT8XgANJP2e9G7Mc1nVY0AYE=; b=Aq1U8sdb7NiZVJWC4vUlChWXOfRbCGaFNjbSpc0WleExMf0SKkQUNrsAlYXljTlC8V kIwakMFlClmc4+G6Yl7CQ/45/9xgObIBveZ7BjUWWP3+FAaW4C1aJyJALPCVD9lXJc+x YJ++0U3IX23F9PeoHw9+6HPC3HlHHljxhgJrbOn5aAgZau7Q6TShdWIkw27qEr4r1db0 ySclaROjZ8pxDb8YfChQRlCjxbFar+IhUVYKk3BD08+hVk5gdraFe163Ypca8nO0QyxZ DsoFqtJh0sAijvTR6s7QSXKCKou0s4gdKPXNW/z/rGUII4CS32K7EojcLfa8YVJI1oAs x6EQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=GsfXoNKONKDKWhJHjg7OT8XgANJP2e9G7Mc1nVY0AYE=; b=5ma3BcWVn3Vl9tihPL5z9o1+efBRhi7SR8Pr85Pmxb+XHJNGFCqmuIWui2kHqUAG3O aDEMzlsK/zWea+pg4lQGSgYgR9MzmCbRtPSN/llHzY4m/A+D0LqzYGyRadOvZpnnjiOI VBJ4WmIOw8RfVZvYboM3aR1zik6qgUUd0EHxcjeZzknKt7UP6MtmDE9ERFec1e1eASKr /NHCg2u/+ZxHkGbNdmC1dN8aF/q7febcfG2BlOkP6SnhL2kwa7s5GuDm+YJnX/etcOsU XDhqx0Bl7SmqM9ART/tLnFn+GEfok39quPp2QHhZjheitvAI1keCzgSS7IDF054tuPTv o7IA== X-Gm-Message-State: AOAM531Zv82RK5p3KGC8OfL9vR8M1EjVs46bR+ilO2GWLqDDhVRnfBbq 8PO3GazRDFErIu+wd0sU2kK3sQ== X-Google-Smtp-Source: ABdhPJy5Bzj+uvdC2D+9IucvrmZ0XZi+3AvPJbXcQc72eVCSrPti9fdcCscTtD01OvFKOzl/PHzgiQ== X-Received: by 2002:a05:6e02:164f:b0:2cf:3244:665d with SMTP id v15-20020a056e02164f00b002cf3244665dmr4183126ilu.170.1651694326903; Wed, 04 May 2022 12:58:46 -0700 (PDT) Received: from google.com (194.225.68.34.bc.googleusercontent.com. [34.68.225.194]) by smtp.gmail.com with ESMTPSA id t13-20020a02ccad000000b0032b3a7817afsm4928792jap.115.2022.05.04.12.58.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 May 2022 12:58:46 -0700 (PDT) Date: Wed, 4 May 2022 19:58:42 +0000 From: Oliver Upton To: Raghavendra Rao Ananta Cc: Marc Zyngier , Andrew Jones , James Morse , Alexandru Elisei , Suzuki K Poulose , Paolo Bonzini , Catalin Marinas , Will Deacon , Peter Shier , Ricardo Koller , Reiji Watanabe , Jing Zhang , linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH] selftests: KVM: aarch64: Let hypercalls use UAPI *_BIT_COUNT Message-ID: References: <20220504184415.1905224-1-rananta@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220504184415.1905224-1-rananta@google.com> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Hi Raghavendra, On Wed, May 04, 2022 at 06:44:15PM +0000, Raghavendra Rao Ananta wrote: > The hypercalls test currently defines its own *_BMAP_BIT_MAX macros to > define the last valid feature bit for each bitmap firmware register. > However, since these definitions are already present in the uapi header, > kvm.h, as *_BMAP_BIT_COUNT, and would help to keep the test updated as > features grow, use these instead. LOL, looks like I lost that one in the end! Still, the fact that you're patching the selftest highlights the fact that there is a nonzero chance of userspace using this value incorrectly expecting it to hold true across all kernels. Since this is the route going forward can we please consider documenting the fact that _BIT_COUNT *will* change and is not stable between kernel versions. Bad UAPI expectations could throw a wrench into this entire plan we've hatched for preserving hypercall ABI. Just a warning at the end of the register documentation would suffice. > No functional change intended. > > Signed-off-by: Raghavendra Rao Ananta Besides considering the above hazard: Reviewed-by: Oliver Upton