[{"id":3682575,"web_url":"http://patchwork.ozlabs.org/comment/3682575/","msgid":"","list_archive_url":null,"date":"2026-04-27T09:17:14","subject":"Re: [PATCH v10 6/7] target/arm/helper: Define cpreg migration\n tolerance for DGBDTR_EL0","submitter":{"id":5111,"url":"http://patchwork.ozlabs.org/api/people/5111/","name":"Peter Maydell","email":"peter.maydell@linaro.org"},"content":"On Mon, 20 Apr 2026 at 15:06, Eric Auger wrote:\n>\n> We want to remove AArch32 DBGDTRTX which was erroneously exposed.\n> This was attempted by 655659a74a36b (\"target/arm: Correct encoding\n> of Debug Communications Channel registers\") but it was discovered\n> that the removal of this debug register broke forward migration on\n> TCG. Now we have the cpreg migration tolerance infrastructure, we\n> can declare one for the DBGDTRTX. This allow to revert the reinstate\n> patch.\n>\n> Signed-off-by: Eric Auger \n> Reviewed-by: Sebastian Ott \n>\n> ---\n>\n> v9 -> v10\n> - Adding a comment explaining why we want a migratoin tolerance\n> for that cpreg\n> ---\n> target/arm/helper.c | 15 +++++++++++++++\n> 1 file changed, 15 insertions(+)\n>\n> diff --git a/target/arm/helper.c b/target/arm/helper.c\n> index 7389f2988c4..d80899cd096 100644\n> --- a/target/arm/helper.c\n> +++ b/target/arm/helper.c\n> @@ -6426,9 +6426,24 @@ void register_cp_regs_for_features(ARMCPU *cpu)\n> .fgt = FGT_CLIDR_EL1,\n> .resetvalue = GET_IDREG(isar, CLIDR)\n> };\n> + uint64_t dbgtr_el0_kvmidx =\n> + cpreg_to_kvm_id(ENCODE_CP_REG(14, 0, 1, 0, 5, 3, 0));\n> +\n> define_one_arm_cp_reg(cpu, &clidr);\n> define_arm_cp_regs(cpu, v7_cp_reginfo);\n> define_debug_regs(cpu);\n> + /**\n> + * AArch32 DBGDTRTX has been introduced with a wrong encoding.\n\nI prefer the phrasing in the old comment here:\n\n\"We used to incorrectly expose a non-existent AArch32 \"DBGDTRTX\" register\nwith this encoding. This was fixed ...\"\n\n> + * This was fixed by commit 655659a74a36 (\"target/arm: Correct\n> + * encoding of Debug Communications Channel registers\") by the\n> + * introduction of correct separate cpreg definitions\n> + * for AA64 and AA32 versions. However the old cpreg definition\n> + * couldn't be removed without breaking the migration. From qemu 11.1\n> + * onwards we can use the migration tolerance infrastructure to\n> + * remove it.\n> + */\n> + arm_register_cpreg_mig_tolerance(cpu, dbgtr_el0_kvmidx,\n> + 0, 0, ToleranceNotOnBothEnds);\n> } else {\n> define_arm_cp_regs(cpu, not_v7_cp_reginfo);\n> }\n\nOtherwise\nReviewed-by: Peter Maydell \n\nthanks\n-- PMM","headers":{"Return-Path":"","X-Original-To":"incoming@patchwork.ozlabs.org","Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=linaro.org header.i=@linaro.org header.a=rsa-sha256\n header.s=google header.b=Jqn6VxkT;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; helo=lists1p.gnu.org;\n envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org;\n receiver=patchwork.ozlabs.org)"],"Received":["from lists1p.gnu.org (lists1p.gnu.org [209.51.188.17])\n\t(using TLSv1.2 with cipher ECDHE-ECDSA-AES256-GCM-SHA384 (256/256 bits))\n\t(No client certificate requested)\n\tby legolas.ozlabs.org (Postfix) with ESMTPS id 4g3yf31ZPQz1yJX\n\tfor ; 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Mon, 27 Apr 2026\n 02:17:26 -0700 (PDT)","MIME-Version":"1.0","References":"<20260420140552.104369-1-eric.auger@redhat.com>\n <20260420140552.104369-7-eric.auger@redhat.com>","In-Reply-To":"<20260420140552.104369-7-eric.auger@redhat.com>","From":"Peter Maydell ","Date":"Mon, 27 Apr 2026 10:17:14 +0100","X-Gm-Features":"AQROBzD2j5W-nVHU8rVmtUyCDS8WzT54HLDhw1z-ez_L5it19FUfHfx-oJm1Npc","Message-ID":"\n ","Subject":"Re: [PATCH v10 6/7] target/arm/helper: Define cpreg migration\n tolerance for DGBDTR_EL0","To":"Eric Auger ","Cc":"eric.auger.pro@gmail.com, qemu-devel@nongnu.org, qemu-arm@nongnu.org,\n cohuck@redhat.com, sebott@redhat.com, peterx@redhat.com, philmd@linaro.org,\n alex.bennee@linaro.org","Content-Type":"text/plain; charset=\"UTF-8\"","Received-SPF":"pass client-ip=2607:f8b0:4864:20::b132;\n envelope-from=peter.maydell@linaro.org; helo=mail-yx1-xb132.google.com","X-Spam_score_int":"-20","X-Spam_score":"-2.1","X-Spam_bar":"--","X-Spam_report":"(-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1,\n DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1,\n RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001,\n SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no","X-Spam_action":"no action","X-BeenThere":"qemu-devel@nongnu.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"qemu development ","List-Unsubscribe":",\n ","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n ","Errors-To":"qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org","Sender":"qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org"}}]