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 X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0B75BC43331 for ; Thu, 26 Mar 2020 09:09:27 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id C67202070A for ; Thu, 26 Mar 2020 09:09:26 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C67202070A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1jHOVh-0004U9-Aa; Thu, 26 Mar 2020 09:09:09 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1jHOVg-0004U4-AY for xen-devel@lists.xenproject.org; Thu, 26 Mar 2020 09:09:08 +0000 X-Inumbo-ID: 724209c8-6f41-11ea-877b-12813bfff9fa Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id 724209c8-6f41-11ea-877b-12813bfff9fa; Thu, 26 Mar 2020 09:09:07 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id ED1ABAF22; Thu, 26 Mar 2020 09:09:05 +0000 (UTC) To: Julien Grall References: <20200322161418.31606-1-julien@xen.org> <20200322161418.31606-5-julien@xen.org> From: Jan Beulich Message-ID: Date: Thu, 26 Mar 2020 10:09:00 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Subject: Re: [Xen-devel] [PATCH 04/17] xen: Convert virt_to_mfn() and mfn_to_virt() to use typesafe MFN X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: Stefano Stabellini , Wei Liu , Konrad Rzeszutek Wilk , Andrew Cooper , Julien Grall , Ian Jackson , George Dunlap , Ross Lagerwall , Lukasz Hawrylko , xen-devel@lists.xenproject.org, Volodymyr Babchuk , =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" On 25.03.2020 19:21, Julien Grall wrote: > On 25/03/2020 15:27, Jan Beulich wrote: >> On 22.03.2020 17:14, julien@xen.org wrote: >>> @@ -785,21 +781,21 @@ bool is_iomem_page(mfn_t mfn) >>>       return (page_get_owner(page) == dom_io); >>>   } >>>   -static int update_xen_mappings(unsigned long mfn, unsigned int cacheattr) >>> +static int update_xen_mappings(mfn_t mfn, unsigned int cacheattr) >>>   { >>>       int err = 0; >>> -    bool alias = mfn >= PFN_DOWN(xen_phys_start) && >>> -         mfn < PFN_UP(xen_phys_start + xen_virt_end - XEN_VIRT_START); >>> +    bool alias = mfn_x(mfn) >= PFN_DOWN(xen_phys_start) && >>> +         mfn_x(mfn) < PFN_UP(xen_phys_start + xen_virt_end - XEN_VIRT_START); >>>       unsigned long xen_va = >>> -        XEN_VIRT_START + ((mfn - PFN_DOWN(xen_phys_start)) << PAGE_SHIFT); >>> +        XEN_VIRT_START + mfn_to_maddr(mfn_add(mfn, -PFN_DOWN(xen_phys_start))); >> >> Depending on the types involved (e.g. in PFN_DOWN()) this may >> or may not be safe, so I consider such a transformation at >> least fragile. I think we either want to gain mfn_sub() or >> keep this as a "real" subtraction. > I want to avoid mfn_x() as much as possible when everything can > be done using typesafe operation. But i am not sure how > mfn_sub() would solve the problem. Do you mind providing more > information? Consider PFN_DOWN() potentially returning "unsigned int". The negation of an unsigned int is still an unsigned int, and hence e.g. -1U (which might result here) is really 0xFFFFFFFF rather than -1L / -1UL as intended. Whereas with mfn_sub() the conversion to unsigned long of the (positive) value to subtract would occur as part of evaluating function arguments, and the resulting subtraction would then be correct. >>> @@ -584,21 +584,21 @@ static unsigned long init_node_heap(int node, unsigned long mfn, >>>           needed = 0; >>>       } >>>       else if ( *use_tail && nr >= needed && >>> -              arch_mfn_in_directmap(mfn + nr) && >>> +              arch_mfn_in_directmap(mfn_x(mfn_add(mfn, nr))) && >>>                 (!xenheap_bits || >>> -               !((mfn + nr - 1) >> (xenheap_bits - PAGE_SHIFT))) ) >>> +               !((mfn_x(mfn) + nr - 1) >> (xenheap_bits - PAGE_SHIFT))) ) >> >> May I suggest consistency here: This one uses +, while ... >> >>>       { >>> -        _heap[node] = mfn_to_virt(mfn + nr - needed); >>> -        avail[node] = mfn_to_virt(mfn + nr - 1) + >>> +        _heap[node] = mfn_to_virt(mfn_add(mfn, nr - needed)); >>> +        avail[node] = mfn_to_virt(mfn_add(mfn, nr - 1)) + >>>                         PAGE_SIZE - sizeof(**avail) * NR_ZONES; >>>       } >>>       else if ( nr >= needed && >>> -              arch_mfn_in_directmap(mfn + needed) && >>> +              arch_mfn_in_directmap(mfn_x(mfn_add(mfn, needed))) && >> >> ... this one uses mfn_add() despite the mfn_x() around it, and ... > > So the reason I used mfn_x(mfn_add(mfn, needed)) here is I plan > to convert arch_mfn_in_directmap() to use typesafe soon. In the > two others cases... > >>>                 (!xenheap_bits || >>> -               !((mfn + needed - 1) >> (xenheap_bits - PAGE_SHIFT))) ) >>> +               !((mfn_x(mfn) + needed - 1) >> (xenheap_bits - PAGE_SHIFT))) ) >> >> ... here you use + again. My personal preference would be to avoid >> constructs like mfn_x(mfn_add()). > > ... I am still unsure how to avoid mfn_x(). Do you have any ideas? I don't see how it can be avoided right now. But I also don't see why - for consistency, as said - you couldn't use mfn_x() also in the middle case. You could then still convert to mfn_add() with that future change of yours. >>> --- a/xen/include/asm-x86/mm.h >>> +++ b/xen/include/asm-x86/mm.h >>> @@ -667,7 +667,7 @@ static inline bool arch_mfn_in_directmap(unsigned long mfn) >>>   { >>>       unsigned long eva = min(DIRECTMAP_VIRT_END, HYPERVISOR_VIRT_END); >>>   -    return mfn <= (virt_to_mfn(eva - 1) + 1); >>> +    return mfn <= mfn_x(mfn_add(virt_to_mfn(eva - 1),  1)); >> >> Even if you wanted to stick to using mfn_add() here, there's one >> blank too many after the comma. > > I will remove the extra blank. Regarding the construction, I have > been wondering for a couple of years now whether we should > introduce mfn_{lt, gt}. What do you think? I too have been wondering, and wouldn't mind their introduction (plus mfn_le / mfn_ge perhaps). But it'll truly help you here anyway only once the function parameter is also mfn_t. Jan