From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CA5FD399358; Mon, 3 Aug 2026 06:32:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785738753; cv=none; b=qV7YF4xC5aVAeGVzPPEUfue7QBJhsCkMrJOalTpgfqxxrp3RbAD7i9G/RnGfLHsJwQWDhfKIT2DQCqqb26Gt6u02bdffPRNHW39FZDur1/XQokm0jFRvd+BKDamhhj6xc5UMKQ32i6EGyXuHOrPz6i6wWbX5vuhhj8BN+M4lbFM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785738753; c=relaxed/simple; bh=AivFDgsImnQT2d9ji2onUVZdA4gMm4SR03L87lUtdtc=; h=Date:Message-ID:From:To:Cc:Subject:In-Reply-To:References: MIME-Version:Content-Type; b=ozxpUP213BU8wusZ3IGBrTjFxsLGR3pdDxlUrpQq/K+yRjwI2Ol8OzHgmY80VT6iokgSlMi2JPMS7UaG6YD/O5Hd3IHgcFro/Iula+QKaRB6mu66eZi6FxhcRXs2MqaPZF36i5OL0GoJuk+MISoFRvSguLFQmFY0T2kJDSU503E= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=GecmZTou; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="GecmZTou" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7C7331F000E9; Mon, 3 Aug 2026 06:32:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785738752; bh=Q003pFrnrktZyIZY/xviIClVkpqPmqmMLUU3EH/6sTA=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=GecmZTouXbNJeH6at4INrHU73sASbBN9fUZHY5eGaKOpuhu9O6CXMrSiDQOpLIKYq G3zJ1ZMkspyesaGvCcz/VAwPqFGbgYivQ9Ci56a3yF6pAwUw8G5GIePLtNY2TiXruQ PCy+PW1m50jIFhTYMCTEPs+hEng/9iBt6/8VWdHq7rb0VRQ025f513OVbpa8NFnm2E fvKgs7YiCqD37X/FIb/6JixPr193kZIoZ065Jmiv2Dn7MAqtTzt7g3MMdiPSiR7XAO SSBmd+EeWXC+mWy3RBUu04dM5vjPWCVCB30xcgtsoAfhMgRf0acKC6UnU9NJDkiu3u sUwctTt1mmwIA== Received: from sofa.misterjones.org ([185.219.108.64] helo=goblin-girl.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.98.2) (envelope-from ) id 1wqmDu-0000000BdF4-0PwR; Mon, 03 Aug 2026 06:32:30 +0000 Date: Mon, 03 Aug 2026 07:32:29 +0100 Message-ID: <868q6nd88y.wl-maz@kernel.org> From: Marc Zyngier To: Karl Mehltretter Cc: Oliver Upton , Suzuki K Poulose , Catalin Marinas , Will Deacon , Andre Przywara , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] KVM: arm64: Preserve GPRs for AArch32 CP64 reads generating an UNDEF In-Reply-To: <20260802182222.2239-1-kmehltretter@gmail.com> References: <20260802182222.2239-1-kmehltretter@gmail.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/30.1 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: kmehltretter@gmail.com, oupton@kernel.org, suzuki.poulose@arm.com, catalin.marinas@arm.com, will@kernel.org, andre.przywara@arm.com, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false On Sun, 02 Aug 2026 19:22:22 +0100, Karl Mehltretter wrote: > > kvm_handle_cp_64() only seeds params.regval for writes. If a CP64 read is > decoded but UNDEFs, emulate_cp() still returns handled and the caller > writes params.regval back to Rt/Rt2. > > This can happen for PMU counter read accesses generating an UNDEF. KVM > injects the exception into the guest, so the MRRC GPRs must remain > unchanged. > > Instead, the uninitialised regval is copied into the guest GPRs. With stack > auto-initialisation this is a deterministic zero or pattern value. With > CONFIG_INIT_STACK_NONE it may be stale host stack data. > > Match kvm_handle_cp_32() and kvm_handle_sys_reg() by seeding regval from > the GPRs before emulation. > > Fixes: 62a89c44954f0 ("arm64: KVM: 32bit handling of coprocessor traps") > Assisted-by: Claude:claude-opus-5 > Signed-off-by: Karl Mehltretter Reviewed-by: Marc Zyngier M. -- Without deviation from the norm, progress is not possible.