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bh=frnGCCkGxm83TmN58QAzuLmNetXVOfr5cHOSW2/PLvM=; b=B3K3SvWGkEczTjZBTejV2t2blURXz3eDr76wrE2Bv2j7fpFBt5kXMpfPE+88PeowdEzICC QUaTguci+L7mz9Cw== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id DFB9313876; Thu, 31 Jul 2025 21:02:26 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id kAU8KOLZi2h8bgAAD6G6ig (envelope-from ); Thu, 31 Jul 2025 21:02:26 +0000 From: Fabiano Rosas To: Peter Maydell , qemu-arm@nongnu.org, qemu-devel@nongnu.org Subject: Re: [PATCH for-10.1] target/arm: Reinstate bogus AArch32 DBGDTRTX register for migration compat In-Reply-To: <20250731134338.250203-1-peter.maydell@linaro.org> References: <20250731134338.250203-1-peter.maydell@linaro.org> Date: Thu, 31 Jul 2025 18:02:23 -0300 Message-ID: <87zfck2hwg.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Queue-Id: 69D571F7ED X-Rspamd-Action: no action X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Spamd-Result: default: False [-4.51 / 50.00]; BAYES_HAM(-3.00)[99.99%]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RCVD_VIA_SMTP_AUTH(0.00)[]; MIME_TRACE(0.00)[0:+]; TO_DN_SOME(0.00)[]; ARC_NA(0.00)[]; MISSING_XM_UA(0.00)[]; RCVD_TLS_ALL(0.00)[]; RCPT_COUNT_THREE(0.00)[3]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:dkim,suse.de:mid,suse.de:email]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; DKIM_TRACE(0.00)[suse.de:+] Received-SPF: pass client-ip=2a07:de40:b251:101:10:150:64:2; envelope-from=farosas@suse.de; helo=smtp-out2.suse.de X-Spam_score_int: -43 X-Spam_score: -4.4 X-Spam_bar: ---- X-Spam_report: (-4.4 / 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_MED=-2.3, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-arm@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-arm-bounces+qemu-arm=archiver.kernel.org@nongnu.org Sender: qemu-arm-bounces+qemu-arm=archiver.kernel.org@nongnu.org Peter Maydell writes: > In commit 655659a74a we fixed some bugs in the encoding of the > Debug Communications Channel registers, including that we were > incorrectly exposing an AArch32 register at p14, 3, c0, c5, 0. > > Unfortunately removing a register is a break of forwards migration > compatibility for TCG, because we will fail the migration if the > source QEMU passes us a cpreg which the destination QEMU does not > have. We don't have a mechanism for saying "it's OK to ignore this > sysreg in the inbound data", so for the 10.1 release reinstate the > incorrect AArch32 register. > > (We probably have had other cases in the past of breaking migration > compatibility like this, but we didn't notice because we didn't test > and in any case not that many people care about TCG migration > compatibility. KVM migration compat is not affected because for KVM > we treat the kernel as the source of truth for what system registers > are present.) > > Fixes: 655659a74a36b ("target/arm: Correct encoding of Debug Communications Channel registers") > Reported-by: Fabiano Rosas > Signed-off-by: Peter Maydell Reviewed-by: Fabiano Rosas