From patchwork Tue Jul 25 05:38:06 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Nikita Shubin X-Patchwork-Id: 13325885 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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 5EB59EB64DD for ; Tue, 25 Jul 2023 05:39:45 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qOAkz-0000p7-73; Tue, 25 Jul 2023 01:38:49 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qOAkX-0000nK-SW; Tue, 25 Jul 2023 01:38:22 -0400 Received: from forward103c.mail.yandex.net ([2a02:6b8:c03:500:1:45:d181:d103]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qOAkU-0001T1-IR; Tue, 25 Jul 2023 01:38:21 -0400 Received: from mail-nwsmtp-smtp-production-main-59.iva.yp-c.yandex.net (mail-nwsmtp-smtp-production-main-59.iva.yp-c.yandex.net [IPv6:2a02:6b8:c0c:1e2b:0:640:94b5:0]) by forward103c.mail.yandex.net (Yandex) with ESMTP id D239060024; Tue, 25 Jul 2023 08:38:08 +0300 (MSK) Received: by mail-nwsmtp-smtp-production-main-59.iva.yp-c.yandex.net (smtp/Yandex) with ESMTPSA id 6cClcVZDfuQ0-WdPkXeM7; Tue, 25 Jul 2023 08:38:08 +0300 X-Yandex-Fwd: 1 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=maquefel.me; s=mail; t=1690263488; bh=qBO2Omcn5BargoaMfiM6gEzoIgFTjptpKB2sMLMlBk0=; h=Message-Id:Date:Cc:Subject:To:From; b=GjibuyiM0Td72mliUJ4qIQmVxaCUgFBJO/scaMnVOEyCaWoTfKtnK3ztiNzY9Yi33 +Ajfy6ySCMr9FL7r+y8ZE7/MkT4cZRo+WCntTqa5BosNudHEYENzukx+3gFVMgw7mT BQncMoqJRt5Z7SClVGTYLN6OxnLRKXKM+2CfowBQ= Authentication-Results: mail-nwsmtp-smtp-production-main-59.iva.yp-c.yandex.net; dkim=pass header.i=@maquefel.me From: Nikita Shubin To: Weiwei Li , Daniel Henrique Barboza , Liu Zhiwei , qemu-riscv@nongnu.org, qemu-devel@nongnu.org Cc: linux@yadro.com, Nikita Shubin Subject: [PATCH] target/riscv: don't read write-only CSR Date: Tue, 25 Jul 2023 08:38:06 +0300 Message-Id: <20230725053806.9463-1-nikita.shubin@maquefel.me> X-Mailer: git-send-email 2.39.2 MIME-Version: 1.0 Received-SPF: pass client-ip=2a02:6b8:c03:500:1:45:d181:d103; envelope-from=nikita.shubin@maquefel.me; helo=forward103c.mail.yandex.net X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org From: Nikita Shubin In case of write-only CSR don't return illegal inst error when CSR is written and lacks read op. Signed-off-by: Nikita Shubin --- Anyway it not might be a good idea to read CSR when we are not asked for, during CSRRW or CSRRWI: "For CSRRWI, if rd=x0, then the instruction shall not read the CSR and shall not cause any of the side effects that might occur on a CSR read." May be i am missing something of course. --- target/riscv/csr.c | 19 +++++++++++-------- 1 file changed, 11 insertions(+), 8 deletions(-) diff --git a/target/riscv/csr.c b/target/riscv/csr.c index ea7585329e..6d6a8821a8 100644 --- a/target/riscv/csr.c +++ b/target/riscv/csr.c @@ -3915,14 +3915,17 @@ static RISCVException riscv_csrrw_do64(CPURISCVState *env, int csrno, return csr_ops[csrno].op(env, csrno, ret_value, new_value, write_mask); } - /* if no accessor exists then return failure */ - if (!csr_ops[csrno].read) { - return RISCV_EXCP_ILLEGAL_INST; - } - /* read old value */ - ret = csr_ops[csrno].read(env, csrno, &old_value); - if (ret != RISCV_EXCP_NONE) { - return ret; + /* don't read if ret_value==NULL */ + if (ret_value) { + /* if no accessor exists then return failure */ + if (!csr_ops[csrno].read) { + return RISCV_EXCP_ILLEGAL_INST; + } + /* read old value */ + ret = csr_ops[csrno].read(env, csrno, &old_value); + if (ret != RISCV_EXCP_NONE) { + return ret; + } } /* write value if writable and write mask set, otherwise drop writes */