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=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,HTML_MESSAGE,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY,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 4B06AC4361B for ; Thu, 10 Dec 2020 12:14:02 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (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 4967E20709 for ; Thu, 10 Dec 2020 12:14:01 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4967E20709 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=c-sky.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:39646 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1knKpc-0002hi-2a for qemu-devel@archiver.kernel.org; Thu, 10 Dec 2020 07:14:00 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:52958) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1knKXO-0008II-FT for qemu-devel@nongnu.org; Thu, 10 Dec 2020 06:55:11 -0500 Received: from smtp2200-217.mail.aliyun.com ([121.197.200.217]:44878) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1knKXJ-0000kA-SQ for qemu-devel@nongnu.org; Thu, 10 Dec 2020 06:55:09 -0500 X-Alimail-AntiSpam: AC=CONTINUE; BC=0.1082813|-1; CH=green; DM=|CONTINUE|false|; DS=CONTINUE|ham_regular_dialog|0.0229386-0.000646465-0.976415; FP=0|0|0|0|0|-1|-1|-1; HT=ay29a033018047203; MF=zhiwei_liu@c-sky.com; NM=1; PH=DS; RN=4; RT=4; SR=0; TI=SMTPD_---.J5TnyRP_1607601286; Received: from 30.225.208.62(mailfrom:zhiwei_liu@c-sky.com fp:SMTPD_---.J5TnyRP_1607601286) by smtp.aliyun-inc.com(10.147.42.22); Thu, 10 Dec 2020 19:54:46 +0800 From: LIU Zhiwei Subject: Re: [PATCH 2/4] target/arm: Fixup contiguous first-fault and no-fault loads To: Richard Henderson , qemu-devel@nongnu.org References: <20201207044655.2312-1-zhiwei_liu@c-sky.com> <20201207044655.2312-3-zhiwei_liu@c-sky.com> <7c6ad308-a2ae-c90b-cac5-19c486b441b3@linaro.org> Message-ID: <88fcf758-4723-3fb7-4a10-ebf23191e0b0@c-sky.com> Date: Thu, 10 Dec 2020 19:54:46 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.5.1 MIME-Version: 1.0 In-Reply-To: <7c6ad308-a2ae-c90b-cac5-19c486b441b3@linaro.org> Content-Type: multipart/alternative; boundary="------------4A3754A2CD88D9CEF1414C3D" Content-Language: en-US Received-SPF: none client-ip=121.197.200.217; envelope-from=zhiwei_liu@c-sky.com; helo=smtp2200-217.mail.aliyun.com X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, HTML_MESSAGE=0.001, NICE_REPLY_A=-0.001, SPF_HELO_NONE=0.001, SPF_NONE=0.001, UNPARSEABLE_RELAY=0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: peter.maydell@linaro.org, alex.bennee@linaro.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" This is a multi-part message in MIME format. --------------4A3754A2CD88D9CEF1414C3D Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit On 2020/12/9 4:16, Richard Henderson wrote: > On 12/6/20 10:46 PM, LIU Zhiwei wrote: >> First-fault or no-fault doesn't mean only access one page. > But the implementation is *allowed* to access only one page. > Thus the comment: > >> - /* >> - * MemSingleNF is allowed to fail for any reason. We have special >> - * code above to handle the first element crossing a page boundary. >> - * As an implementation choice, decline to handle a cross-page element >> - * in any other position. >> - */ From the pseudo code,  I see  that we should handle the first element in first-fault follow Mem. And the other elements in this function should follow  MemNF. I have some questions here： 1. Why  do special process to the first element if it crosses pages in no-fault? Because it's not aligned? // MemNF[] - non-assignment form // ============================= (bits(8*size), boolean) MemNF[bits(64) address, integer size, AccType acctype] assert size IN {1, 2, 4, 8, 16}; bits(8*size) value; aligned = (address == Align(address, size)); A = SCTLR[].A; if !aligned && (A == '1') then     return (bits(8*size) UNKNOWN, TRUE); atomic = aligned || size == 1; if !atomic then     (value<7:0>, bad) = MemSingleNF[address, 1, acctype, aligned];     if bad then         return (bits(8*size) UNKNOWN, TRUE);     // For subsequent bytes it is CONSTRAINED UNPREDICTABLE whether an unaligned Device memory     // access will generate an Alignment Fault, as to get this far means the first byte did     // not, so we must be changing to a new translation page.     if !aligned then     c = ConstrainUnpredictable(Unpredictable_DEVPAGE2);     assert c IN {Constraint_FAULT, Constraint_NONE};     if c == Constraint_NONE then aligned = TRUE;     for i = 1 to size-1         (value<8*i+7:8*i>, bad) = MemSingleNF[address+i, 1, acctype, aligned];     if bad then         return (bits(8*size) UNKNOWN, TRUE); else     (value, bad) = MemSingleNF[address, size, acctype, aligned];     if bad then         return (bits(8*size) UNKNOWN, TRUE); return (value, FALSE); 2.  Why it doesn't access the second page like the first page? I think they should obey the same MemSingleNF implementation. > r~ --------------4A3754A2CD88D9CEF1414C3D Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: 8bit

On 2020/12/9 4:16, Richard Henderson wrote:
On 12/6/20 10:46 PM, LIU Zhiwei wrote:

First-fault or no-fault doesn't mean only access one page.

But the implementation is *allowed* to access only one page.
Thus the comment:


-    /*
-     * MemSingleNF is allowed to fail for any reason.  We have special
-     * code above to handle the first element crossing a page boundary.
-     * As an implementation choice, decline to handle a cross-page element
-     * in any other position.
-     */
From the pseudo code,  I see  that we should handle the first element in first-fault follow Mem. And the other elements in this function should follow  MemNF.

I have some questions here：

1. Why  do special process to the first element if it crosses pages in no-fault? Because it's not aligned?

// MemNF[] - non-assignment form
// =============================
(bits(8*size), boolean) MemNF[bits(64) address, integer size, AccType acctype]
assert size IN {1, 2, 4, 8, 16};
bits(8*size) value;
aligned = (address == Align(address, size));
A = SCTLR[].A;
if !aligned && (A == '1') then
    return (bits(8*size) UNKNOWN, TRUE);
atomic = aligned || size == 1;
if !atomic then
    (value<7:0>, bad) = MemSingleNF[address, 1, acctype, aligned];
    if bad then
        return (bits(8*size) UNKNOWN, TRUE);
    // For subsequent bytes it is CONSTRAINED UNPREDICTABLE whether an unaligned Device memory
    // access will generate an Alignment Fault, as to get this far means the first byte did
    // not, so we must be changing to a new translation page.
    if !aligned then
           c = ConstrainUnpredictable(Unpredictable_DEVPAGE2);
    assert c IN {Constraint_FAULT, Constraint_NONE};
    if c == Constraint_NONE then aligned = TRUE;
    for i = 1 to size-1
        (value<8*i+7:8*i>, bad) = MemSingleNF[address+i, 1, acctype, aligned];
    if bad then
        return (bits(8*size) UNKNOWN, TRUE);
else
    (value, bad) = MemSingleNF[address, size, acctype, aligned];
    if bad then
        return (bits(8*size) UNKNOWN, TRUE);
return (value, FALSE);


2.  Why it doesn't access the second page like the first page? I think they should obey the same MemSingleNF implementation.

r~

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