From mboxrd@z Thu Jan 1 00:00:00 1970 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 D8E3ECA0FED for ; Tue, 9 Sep 2025 08:16:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=1sCkCgaiG1tA44yfM5L2ANo4vr5hbJ7W7Dhy275RGto=; b=NoJ2t0Y1rETI7SLhCqDHak7hAg r6qLkRVK7XxIw5vnAGC+1MQdhsmmczFNG9xnXuNMFJSmuSboKxdu5rJ2J2DIL17vrEn6UGLg0W/Nj dWzlV160mfsN2I8JKiLU6+VHmcMXZcKJqHO3IJmICylsQ2NwC0prVrBTcvRiOiXikOct62XNCWiEU IQgUpGTMfebzmaNJwlXFwpbqGzjGFMgxm/cYdFpu8W/lAfISUvU3aInTdaFKVKxtKmGNfVNh+66j/ XsJVQ3uyRyk9T7/MPuCD5HUV81eZK3eQFIRTiUzvu0wTEi+onLF9vm+WDdokln+9WujU+ItoIkF0A yjHk4L9A==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1uvtWi-00000005VdB-2kXr; Tue, 09 Sep 2025 08:16:32 +0000 Received: from out-180.mta0.migadu.com ([91.218.175.180]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1uvsRm-000000053E8-1stt for linux-arm-kernel@lists.infradead.org; Tue, 09 Sep 2025 07:07:23 +0000 Date: Tue, 9 Sep 2025 00:07:15 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1757401640; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=1sCkCgaiG1tA44yfM5L2ANo4vr5hbJ7W7Dhy275RGto=; b=T16KC8mlkc5FGJYRuNmRzyykNMCR64eNY9Ro4AI2qiVGUT9isxX9alIMp3XWcO7yseGGfg BnOhQMDKGXI7yO4Cpi9xkcifSVD8E2ML6BOsNywRtslYQYzYHm9KCO91uDTv60onUenJMg 9kPyXnW9BljanSa6ge2DE3kT/RI9Ezw= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Oliver Upton To: Jinqian Yang Cc: yuzenghui@huawei.com, maz@kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, liuyonglong@huawei.com, wangzhou1@hisilicon.com Subject: Re: [PATCH v2 1/3] KVM: arm64: Make ID_AA64MMFR1_EL1.HCX writable from userspace Message-ID: References: <20250909034415.3822478-1-yangjinqian1@huawei.com> <20250909034415.3822478-2-yangjinqian1@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250909034415.3822478-2-yangjinqian1@huawei.com> X-Migadu-Flow: FLOW_OUT X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250909_000722_640122_187030D9 X-CRM114-Status: UNSURE ( 8.96 ) X-CRM114-Notice: Please train this message. X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Sep 09, 2025 at 11:44:13AM +0800, Jinqian Yang wrote: > Allow userspace to downgrade HCX in ID_AA64MMFR1_EL1. Userspace can > only change this value from high to low. > > Signed-off-by: Jinqian Yang I'm not sure our quality of emulation is that great in this case. We have no way of trapping the register and it is always stateful. Better yet, our RESx infrastructure doesn't account for the presence of FEAT_HCX and we happily merge the contents with the host's HCRX. We should make a reasonable attempt at upholding the architecture before allowing userspace to de-feature FEAT_HCX. Thanks, Oliver