From nobody Mon May 20 01:44:47 2024 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) client-ip=208.118.235.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zohomail.com; dkim=fail; spf=pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org Return-Path: Received: from lists.gnu.org (208.118.235.17 [208.118.235.17]) by mx.zohomail.com with SMTPS id 1522180626066721.2675943202981; Tue, 27 Mar 2018 12:57:06 -0700 (PDT) Received: from localhost ([::1]:35839 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1f0uiI-0004y3-29 for importer@patchew.org; Tue, 27 Mar 2018 15:56:58 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45292) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1f0uh2-0004M0-0p for qemu-devel@nongnu.org; Tue, 27 Mar 2018 15:55:41 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1f0ugy-0005Aq-3Z for qemu-devel@nongnu.org; Tue, 27 Mar 2018 15:55:40 -0400 Received: from mail-pl0-x243.google.com ([2607:f8b0:400e:c01::243]:38945) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1f0ugx-0005AN-Ti for qemu-devel@nongnu.org; Tue, 27 Mar 2018 15:55:36 -0400 Received: by mail-pl0-x243.google.com with SMTP id s24-v6so64847plq.6 for ; Tue, 27 Mar 2018 12:55:35 -0700 (PDT) Received: from monty.com ([12.206.222.5]) by smtp.gmail.com with ESMTPSA id p1sm4336686pgr.67.2018.03.27.12.55.33 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Tue, 27 Mar 2018 12:55:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sifive.com; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=FmYgorCnXIjKTbWTKI+d3/vjhL5I6b1a2DTUTRpA7DU=; b=iaKvFwfk/AFsPY0JjygkeEX9mK19gw6nKsLerZKQQ3QkbMUGzfsRt0gmOEJBIdgtvq CWfLpEMt6S7VzA7JMiBUJfHiXgRA9CadpyG3MJAxDLlym8eoTkcrjiQuZyZImhx9iErZ aghtVLQJbfnIQwrVsMx5hCcyoro1GzQQlyKR6oDwtXr5bQzJnWfr2cKmFONkdj+2Xa4F edFZroWS6eZfzZOJzk7cUZp83Dr4xH4UIpff5cn518SlJE3ssCcNhDD9Hj2ys9R669rC C607p7SEeLmhfcfV0sKZBSVyqcOl+cLABMQUx1YM27fLtrH66YX8jRJQKw7jnmOgL8oN Yb9g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=FmYgorCnXIjKTbWTKI+d3/vjhL5I6b1a2DTUTRpA7DU=; b=oL/zifNLVwAagZ1XlQVGPJzMTJ5dNWv9B/PrR+GSxn24Q5IdMZfT+g5c/hD3vYlkXB BV4RsyTOOKU6IZzfKjoLNKdNA4Wr/fNEpa6DYQFfT+/YTvP/sZWzaNPqwlE7Wgd+N5kv L2CvsshUXKWMOSGOddJWLL+B/bN8De3s7O6gIv5Iwp2MH412EFefm7+mZm91eEECLN0Y y40a2REt5NlfCKoMz3el39diGa5InCNXlW+hIH2BRb6y3GwfjluTpVUincErlev8pxH/ W/ZpiKNavHXbaU82Oo/bAUUZLnK90IfoQ/lySwjJqFqLtGUvKcyXN7PR7HnRhzR6pAOu /gCw== X-Gm-Message-State: AElRT7G1NlEU06br6EaqV148/njbH6fLpf8qVgw7b6WPvT+NtasRV0UZ Bb/vKFO7kPK3+XbalcGfpWA758acR/w= X-Google-Smtp-Source: AIpwx48KTT8+3cNX+ZRBw8LHpG94Ni+pqJ1gU/KEMm1jmJPsbmf3GJbW3lZvGy+MkAQNPqm5kTNH+Q== X-Received: by 2002:a17:902:b414:: with SMTP id x20-v6mr651106plr.165.1522180534889; Tue, 27 Mar 2018 12:55:34 -0700 (PDT) From: Michael Clark To: qemu-devel@nongnu.org Date: Tue, 27 Mar 2018 12:54:47 -0700 Message-Id: <1522180487-22899-2-git-send-email-mjc@sifive.com> X-Mailer: git-send-email 2.7.0 In-Reply-To: <1522180487-22899-1-git-send-email-mjc@sifive.com> References: <1522180487-22899-1-git-send-email-mjc@sifive.com> X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 2607:f8b0:400e:c01::243 Subject: [Qemu-devel] [PATCH v1 1/1] RISC-V: Workaround for critical mstatus.FS MTTCG bug X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , Sagar Karandikar , Bastian Koppelmann , Palmer Dabbelt , Michael Clark , patches@groups.riscv.org Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: fail (Header signature does not verify) X-ZohoMail: RDKM_2 RSF_0 Z_629925259 SPT_0 Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" This change is a workaround for a bug where mstatus.FS is not correctly reporting dirty when MTTCG and SMP are enabled which results in the floating point register file not being saved during context switches. This a critical bug for RISC-V in QEMU as it results in floating point register file corruption when running SMP Linux in the RISC-V 'virt' machine. This workaround will return dirty if mstatus.FS is switched from off to initial or clean. We have checked the specification and it is legal for an implementation to return either off, or dirty, if set to initial or clean. This workaround will result in unnecessary floating point save restore. When mstatus.FS is off, floating point instruction trap to indicate the process is using the FPU. The OS can then save floating-point state of the previous process using the FPU and set mstatus.FS to initial or clean. With this workaround, mstatus.FS will always return dirty if set to a non-zero value, indicating floating point save restore is necessary, versus misreporting mstatus.FS resulting in floating point register file corruption. Cc: Palmer Dabbelt Cc: Sagar Karandikar Cc: Bastian Koppelmann Cc: Peter Maydell Tested-by: Richard W.M. Jones Signed-off-by: Michael Clark Reviewed-By: Palmer Dabbelt --- target/riscv/op_helper.c | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) diff --git a/target/riscv/op_helper.c b/target/riscv/op_helper.c index e34715d..7281b98 100644 --- a/target/riscv/op_helper.c +++ b/target/riscv/op_helper.c @@ -144,8 +144,23 @@ void csr_write_helper(CPURISCVState *env, target_ulong= val_to_write, } =20 mstatus =3D (mstatus & ~mask) | (val_to_write & mask); - int dirty =3D (mstatus & MSTATUS_FS) =3D=3D MSTATUS_FS; - dirty |=3D (mstatus & MSTATUS_XS) =3D=3D MSTATUS_XS; + + /* Note: this is a workaround for an issue where mstatus.FS + does not report dirty when SMP and MTTCG is enabled. This + workaround is technically compliant with the RISC-V Privileged + specification as it is legal to return only off, or dirty, + however this may cause unnecessary saves of floating point stat= e. + Without this workaround, floating point state is not saved and + restored correctly when SMP and MTTCG is enabled, */ + if (qemu_tcg_mttcg_enabled()) { + /* FP is always dirty or off */ + if (mstatus & MSTATUS_FS) { + mstatus |=3D MSTATUS_FS; + } + } + + int dirty =3D ((mstatus & MSTATUS_FS) =3D=3D MSTATUS_FS) | + ((mstatus & MSTATUS_XS) =3D=3D MSTATUS_XS); mstatus =3D set_field(mstatus, MSTATUS_SD, dirty); env->mstatus =3D mstatus; break; --=20 2.7.0