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Thu, 16 Apr 2020 16:26:05 +0100 MIME-Version: 1.0 Date: Thu, 16 Apr 2020 16:26:05 +0100 From: Marc Zyngier To: Suzuki K Poulose Subject: Re: [PATCH 8/8] arm64: cpufeature: Add an overview comment for the cpufeature framework In-Reply-To: <96dd797d-ccfe-c867-0a70-65eccacde3cd@arm.com> References: <20200414213114.2378-1-will@kernel.org> <20200414213114.2378-9-will@kernel.org> <96dd797d-ccfe-c867-0a70-65eccacde3cd@arm.com> Message-ID: <96438d59a2bc05871ef68fca475fabf5@kernel.org> X-Sender: maz@kernel.org User-Agent: Roundcube Webmail/1.3.10 X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: suzuki.poulose@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, mark.rutland@arm.com, anshuman.khandual@arm.com, catalin.marinas@arm.com, saiprakash.ranjan@codeaurora.org, dianders@chromium.org, kernel-team@android.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Cc: saiprakash.ranjan@codeaurora.org, kernel-team@android.com, anshuman.khandual@arm.com, catalin.marinas@arm.com, linux-kernel@vger.kernel.org, dianders@chromium.org, will@kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu On 2020-04-16 15:59, Suzuki K Poulose wrote: Hi Suzuki, [...] > As you mentioned in the other response we could add information about > the guest view, something like : > > - KVM exposes the sanitised value of the feature registers to the > guests and is not affected by the FTR_VISIBLE. However, > depending on the individual feature support in the hypervisor, > some of the fields may be capped/limited. Although in most cases, what KVM exposes is indeed a strict subset of the host's features, there is a few corner cases where we expose features that do not necessarily exist on the host. For example ARMv8.5-GTG and ARMv8.4-TTL get exposed by the NV patches even if they don't exist on the host, as KVM will actually emulate them. Not a big deal, but I just wanted to outline that it isn't as clear-cut as it may seem... Thanks, M. -- Jazz is not dead. It just smells funny... _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm 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 X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 43996C2BB55 for ; Thu, 16 Apr 2020 15:28:03 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 12606214D8 for ; Thu, 16 Apr 2020 15:28:03 +0000 (UTC) Authentication-Results: mail.kernel.org; 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Thu, 16 Apr 2020 15:26:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1587050767; bh=9UZrlX86YbwbreLTFi5YKGq3YhBn1+9uHoeSBBf886o=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=Wro98QecVB/0yTP1mFZaDqaN8sf50x8/37MZzrvNgiLKrQBlnQ6sup5XaruO0XJ92 Ov5TZHt+/at8yAP5S0jEpEatpociE0KfOEDnJhmaFF8XEYMeoULpW57GUqGQWwHoJs gxSvPKSjW6ewRrdRcYKlexr5vTiEok4qN9+lJFbQ= Received: from disco-boy.misterjones.org ([51.254.78.96] helo=www.loen.fr) by disco-boy.misterjones.org with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1jP6Oz-003uSn-HM; Thu, 16 Apr 2020 16:26:05 +0100 MIME-Version: 1.0 Date: Thu, 16 Apr 2020 16:26:05 +0100 From: Marc Zyngier To: Suzuki K Poulose Subject: Re: [PATCH 8/8] arm64: cpufeature: Add an overview comment for the cpufeature framework In-Reply-To: <96dd797d-ccfe-c867-0a70-65eccacde3cd@arm.com> References: <20200414213114.2378-1-will@kernel.org> <20200414213114.2378-9-will@kernel.org> <96dd797d-ccfe-c867-0a70-65eccacde3cd@arm.com> Message-ID: <96438d59a2bc05871ef68fca475fabf5@kernel.org> X-Sender: maz@kernel.org User-Agent: Roundcube Webmail/1.3.10 X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: suzuki.poulose@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, mark.rutland@arm.com, anshuman.khandual@arm.com, catalin.marinas@arm.com, saiprakash.ranjan@codeaurora.org, dianders@chromium.org, kernel-team@android.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200416_082607_693052_F398F0F6 X-CRM114-Status: GOOD ( 11.90 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: mark.rutland@arm.com, saiprakash.ranjan@codeaurora.org, kernel-team@android.com, anshuman.khandual@arm.com, catalin.marinas@arm.com, linux-kernel@vger.kernel.org, dianders@chromium.org, will@kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2020-04-16 15:59, Suzuki K Poulose wrote: Hi Suzuki, [...] > As you mentioned in the other response we could add information about > the guest view, something like : > > - KVM exposes the sanitised value of the feature registers to the > guests and is not affected by the FTR_VISIBLE. However, > depending on the individual feature support in the hypervisor, > some of the fields may be capped/limited. Although in most cases, what KVM exposes is indeed a strict subset of the host's features, there is a few corner cases where we expose features that do not necessarily exist on the host. For example ARMv8.5-GTG and ARMv8.4-TTL get exposed by the NV patches even if they don't exist on the host, as KVM will actually emulate them. Not a big deal, but I just wanted to outline that it isn't as clear-cut as it may seem... Thanks, M. -- Jazz is not dead. It just smells funny... _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel 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 X-Spam-Level: X-Spam-Status: No, score=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3EE08C2BB55 for ; Thu, 16 Apr 2020 15:27:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 13032206D6 for ; Thu, 16 Apr 2020 15:27:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1587050821; bh=9UZrlX86YbwbreLTFi5YKGq3YhBn1+9uHoeSBBf886o=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=auDVwaT/vEXmzwmIzT9/Njl2UjVQ5LHtty4xFSLcoXEB0Jm1dv7SaIvcG2F9wpxjW UwSGEPL3flNexyVdnlWNb6HvT5DR5UDWBVeU83m2i76MD94aJ6uUZZh0y0mzZi5nOZ /lEPTrwyBIgjwpoPUQiuXxAupPj3wUuMS3zw3Mzw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2410283AbgDPP1A (ORCPT ); Thu, 16 Apr 2020 11:27:00 -0400 Received: from mail.kernel.org ([198.145.29.99]:39462 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2391156AbgDPP0I (ORCPT ); Thu, 16 Apr 2020 11:26:08 -0400 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 203D7214D8; Thu, 16 Apr 2020 15:26:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1587050767; bh=9UZrlX86YbwbreLTFi5YKGq3YhBn1+9uHoeSBBf886o=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=Wro98QecVB/0yTP1mFZaDqaN8sf50x8/37MZzrvNgiLKrQBlnQ6sup5XaruO0XJ92 Ov5TZHt+/at8yAP5S0jEpEatpociE0KfOEDnJhmaFF8XEYMeoULpW57GUqGQWwHoJs gxSvPKSjW6ewRrdRcYKlexr5vTiEok4qN9+lJFbQ= Received: from disco-boy.misterjones.org ([51.254.78.96] helo=www.loen.fr) by disco-boy.misterjones.org with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1jP6Oz-003uSn-HM; Thu, 16 Apr 2020 16:26:05 +0100 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Thu, 16 Apr 2020 16:26:05 +0100 From: Marc Zyngier To: Suzuki K Poulose Cc: will@kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, mark.rutland@arm.com, anshuman.khandual@arm.com, catalin.marinas@arm.com, saiprakash.ranjan@codeaurora.org, dianders@chromium.org, kernel-team@android.com Subject: Re: [PATCH 8/8] arm64: cpufeature: Add an overview comment for the cpufeature framework In-Reply-To: <96dd797d-ccfe-c867-0a70-65eccacde3cd@arm.com> References: <20200414213114.2378-1-will@kernel.org> <20200414213114.2378-9-will@kernel.org> <96dd797d-ccfe-c867-0a70-65eccacde3cd@arm.com> Message-ID: <96438d59a2bc05871ef68fca475fabf5@kernel.org> X-Sender: maz@kernel.org User-Agent: Roundcube Webmail/1.3.10 X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: suzuki.poulose@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, mark.rutland@arm.com, anshuman.khandual@arm.com, catalin.marinas@arm.com, saiprakash.ranjan@codeaurora.org, dianders@chromium.org, kernel-team@android.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-04-16 15:59, Suzuki K Poulose wrote: Hi Suzuki, [...] > As you mentioned in the other response we could add information about > the guest view, something like : > > - KVM exposes the sanitised value of the feature registers to the > guests and is not affected by the FTR_VISIBLE. However, > depending on the individual feature support in the hypervisor, > some of the fields may be capped/limited. Although in most cases, what KVM exposes is indeed a strict subset of the host's features, there is a few corner cases where we expose features that do not necessarily exist on the host. For example ARMv8.5-GTG and ARMv8.4-TTL get exposed by the NV patches even if they don't exist on the host, as KVM will actually emulate them. Not a big deal, but I just wanted to outline that it isn't as clear-cut as it may seem... Thanks, M. -- Jazz is not dead. It just smells funny...