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=-8.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 98821C433E6 for ; Mon, 31 Aug 2020 00:07:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 54FB020720 for ; Mon, 31 Aug 2020 00:07:02 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=ozlabs-ru.20150623.gappssmtp.com header.i=@ozlabs-ru.20150623.gappssmtp.com header.b="TlXIB4Mp" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726607AbgHaAHA (ORCPT ); Sun, 30 Aug 2020 20:07:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52998 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726396AbgHaAG5 (ORCPT ); Sun, 30 Aug 2020 20:06:57 -0400 Received: from mail-pl1-x643.google.com (mail-pl1-x643.google.com [IPv6:2607:f8b0:4864:20::643]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B7450C061573 for ; Sun, 30 Aug 2020 17:06:56 -0700 (PDT) Received: by mail-pl1-x643.google.com with SMTP id q3so2195120pls.11 for ; Sun, 30 Aug 2020 17:06:56 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ozlabs-ru.20150623.gappssmtp.com; s=20150623; h=subject:to:cc:references:from:autocrypt:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=dPg6pIp0d6+IMW2eCyPuihZz92GIZill6IOikyCStwY=; b=TlXIB4MpnJHxFvHJueLLfeaBG1G6nE8C+Egk4sOkfAP8/FrCz60fAICJztXIiP0kNs eUtXcJ1UPbC4MblKNLR48Y/UkPiok4rV15/bKrR+/B/GvzwC5scvbkVZjHJUZg3SNAXL JZ2Nxu85goPVtOHPv2/ec6yYY+7b2KMUqLz5AUR8+gFbyS2NewAMUUyhy06ZuSXfOvxg 7OcTPPIejcgFuUYW2/APHNLE/bBsU2QHXVAlr2K5fPnl72ynnkzrc4IkRn5U6Uy+hvcR 5B7i1AQfAw8LHe7kQvXwxdAdUCO/vrpJELso/hjD2nvOuY2lQa7ws5BmHar1i3MLJMuR 3/ZA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:autocrypt :message-id:date:user-agent:mime-version:in-reply-to :content-language:content-transfer-encoding; bh=dPg6pIp0d6+IMW2eCyPuihZz92GIZill6IOikyCStwY=; b=rlV0NoOlD4CvBU00odeM7nSKgyRYROrFgM+EclBtRsN0SnehgJLfKmzswP+BND6zNl 6j/P146Fed0CIJQ3zttTFsveZjhw1KcsPn4EYqJkwjAM05/Zs2CAZpMDFXq1L05MihpM tq3h4ZrXFF+Jdl6QV4+UWGsc5FVTaPON38x9VTeLWhPibx2UhjZJ1nC6Asu+9DO3mV3P f989/T0SGmOxI2brK0N0qS8Gi2AepokNVPcHYJbgLLy7W5PIfHWHuFr3LHi6xXXtwFr7 wRZAfTJeqPivVAJgprHKyMfXcZtXYXyn6yi9xmsWsNKbcLxchwjlbXuiTBPeotmFtO4N 4Fmg== X-Gm-Message-State: AOAM533oyAC77UN6wJ1cZLmQQh0FZV0P8u/Q51+vJ+D2GPpuMPCvX0RW br6WkNF/aLVhMfS7wW7i0HPaW6oSuh7XNA== X-Google-Smtp-Source: ABdhPJzDxhtQpxEwUEtVv5mpaSy+ixf9hbfjwDfZwDB111Xo6VzJEX7Z661UBYIL64R/ele2CHSgEA== X-Received: by 2002:a17:90b:245:: with SMTP id fz5mr3537237pjb.131.1598832415794; Sun, 30 Aug 2020 17:06:55 -0700 (PDT) Received: from [192.168.10.94] (124-171-83-152.dyn.iinet.net.au. [124.171.83.152]) by smtp.gmail.com with ESMTPSA id y5sm1833839pge.62.2020.08.30.17.06.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 30 Aug 2020 17:06:54 -0700 (PDT) Subject: Re: [PATCH v1 01/10] powerpc/pseries/iommu: Replace hard-coded page shift To: Leonardo Bras , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , Christophe Leroy , Joel Stanley , Thiago Jung Bauermann , Ram Pai , Brian King , Murilo Fossa Vicentini , David Dai Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org References: <20200817234033.442511-1-leobras.c@gmail.com> <20200817234033.442511-2-leobras.c@gmail.com> <6232948f-033d-8322-e656-544f12c5f784@ozlabs.ru> <31e913d842693b6e107cb2b8e51fd45118b1bd2c.camel@gmail.com> <1e77a3d9-dff9-f58b-45be-77be7cbea41a@ozlabs.ru> <93037398c7afaabc0411890998f3f29f741c8aff.camel@gmail.com> From: Alexey Kardashevskiy Autocrypt: addr=aik@ozlabs.ru; keydata= mQINBE+rT0sBEADFEI2UtPRsLLvnRf+tI9nA8T91+jDK3NLkqV+2DKHkTGPP5qzDZpRSH6mD 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ikTJSxWUKmh7OP5mrqhwNe0ezgGiWxxvyNwThOHc5JvpzJLd32VDFilbxgu4Hhnf6LcgZJ2c Zd44XWqUu7FzVOYaSgIvTP0hNrBYm/E6M7yrLbs3JY74fGzPWGRbBUHTZXQEqQnZglXaVB5V ZhSFtHopZnBSCUSNDbB+QGy4B/E++Bb02IBTGl/JxmOwG+kZUnymsPvTtnNIeTLHxN/H/ae0 c7E5M+/NpslPCmYnDjs5qg0/3ihh6XuOGggZQOqrYPC3PnsNs3NxirwOkVPQgO6mXxpuifvJ DG9EMkK8IBXnLulqVk54kf7fE0jT/d8RTtJIA92GzsgdK2rpT1MBKKVffjRFGwN7nQVOzi4T XrB5p+6ML7Bd84xOEGsj/vdaXmz1esuH7BOZAGEZfLRCHJ0GVCSssg== Message-ID: Date: Mon, 31 Aug 2020 10:06:47 +1000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <93037398c7afaabc0411890998f3f29f741c8aff.camel@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 29/08/2020 05:55, Leonardo Bras wrote: > On Fri, 2020-08-28 at 12:27 +1000, Alexey Kardashevskiy wrote: >> >> On 28/08/2020 01:32, Leonardo Bras wrote: >>> Hello Alexey, thank you for this feedback! >>> >>> On Sat, 2020-08-22 at 19:33 +1000, Alexey Kardashevskiy wrote: >>>>> +#define TCE_RPN_BITS 52 /* Bits 0-51 represent RPN on TCE */ >>>> >>>> Ditch this one and use MAX_PHYSMEM_BITS instead? I am pretty sure this >>>> is the actual limit. >>> >>> I understand this MAX_PHYSMEM_BITS(51) comes from the maximum physical memory addressable in the machine. IIUC, it means we can access physical address up to (1ul << MAX_PHYSMEM_BITS). >>> >>> This 52 comes from PAPR "Table 9. TCE Definition" which defines bits >>> 0-51 as the RPN. By looking at code, I understand that it means we may input any address < (1ul << 52) to TCE. >>> >>> In practice, MAX_PHYSMEM_BITS should be enough as of today, because I suppose we can't ever pass a physical page address over >>> (1ul << 51), and TCE accepts up to (1ul << 52). >>> But if we ever increase MAX_PHYSMEM_BITS, it doesn't necessarily means that TCE_RPN_BITS will also be increased, so I think they are independent values. >>> >>> Does it make sense? Please let me know if I am missing something. >> >> The underlying hardware is PHB3/4 about which the IODA2 Version 2.4 >> 6Apr2012.pdf spec says: >> >> "The number of most significant RPN bits implemented in the TCE is >> dependent on the max size of System Memory to be supported by the platform". >> >> IODA3 is the same on this matter. >> >> This is MAX_PHYSMEM_BITS and PHB itself does not have any other limits >> on top of that. So the only real limit comes from MAX_PHYSMEM_BITS and >> where TCE_RPN_BITS comes from exactly - I have no idea. > > Well, I created this TCE_RPN_BITS = 52 because the previous mask was a > hardcoded 40-bit mask (0xfffffffffful), for hard-coded 12-bit (4k) > pagesize, and on PAPR+/LoPAR also defines TCE as having bits 0-51 > described as RPN, as described before. > > IODA3 Revision 3.0_prd1 (OpenPowerFoundation), Figure 3.4 and 3.5. > shows system memory mapping into a TCE, and the TCE also has bits 0-51 > for the RPN (52 bits). "Table 3.6. TCE Definition" also shows it. >> In fact, by the looks of those figures, the RPN_MASK should always be a > 52-bit mask, and RPN = (page >> tceshift) & RPN_MASK. I suspect the mask is there in the first place for extra protection against too big addresses going to the TCE table (or/and for virtial vs physical addresses). Using 52bit mask makes no sense for anything, you could just drop the mask and let c compiler deal with 64bit "uint" as it is basically a 4K page address anywhere in the 64bit space. Thanks, > Maybe that's it? > >> >> >>>> >>>>> +#define TCE_RPN_MASK(ps) ((1ul << (TCE_RPN_BITS - (ps))) - 1) >>>>> #define TCE_VALID 0x800 /* TCE valid */ >>>>> #define TCE_ALLIO 0x400 /* TCE valid for all lpars */ >>>>> #define TCE_PCI_WRITE 0x2 /* write from PCI allowed */ >>>>> diff --git a/arch/powerpc/platforms/pseries/iommu.c b/arch/powerpc/platforms/pseries/iommu.c >>>>> index e4198700ed1a..8fe23b7dff3a 100644 >>>>> --- a/arch/powerpc/platforms/pseries/iommu.c >>>>> +++ b/arch/powerpc/platforms/pseries/iommu.c >>>>> @@ -107,6 +107,9 @@ static int tce_build_pSeries(struct iommu_table *tbl, long index, >>>>> u64 proto_tce; >>>>> __be64 *tcep; >>>>> u64 rpn; >>>>> + const unsigned long tceshift = tbl->it_page_shift; >>>>> + const unsigned long pagesize = IOMMU_PAGE_SIZE(tbl); >>>>> + const u64 rpn_mask = TCE_RPN_MASK(tceshift); >>>> >>>> Using IOMMU_PAGE_SIZE macro for the page size and not using >>>> IOMMU_PAGE_MASK for the mask - this incosistency makes my small brain >>>> explode :) I understand the history but maaaaan... Oh well, ok. >>>> >>> >>> Yeah, it feels kind of weird after two IOMMU related consts. :) >>> But sure IOMMU_PAGE_MASK() would not be useful here :) >>> >>> And this kind of let me thinking: >>>>> + rpn = __pa(uaddr) >> tceshift; >>>>> + *tcep = cpu_to_be64(proto_tce | (rpn & rpn_mask) << tceshift); >>> Why not: >>> rpn_mask = TCE_RPN_MASK(tceshift) << tceshift; >> >> A mask for a page number (but not the address!) hurts my brain, masks >> are good against addresses but numbers should already have all bits >> adjusted imho, may be it is just me :-/ >> >> >>> >>> rpn = __pa(uaddr) & rpn_mask; >>> *tcep = cpu_to_be64(proto_tce | rpn) >>> >>> I am usually afraid of changing stuff like this, but I think it's safe. >>> >>>> Good, otherwise. Thanks, >>> >>> Thank you for reviewing! >>> >>> >>> > -- Alexey