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=-9.8 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS autolearn=unavailable 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 550A0C433DF for ; Thu, 13 Aug 2020 09:52:21 +0000 (UTC) Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by mail.kernel.org (Postfix) with ESMTP id CD7DE2078D for ; Thu, 13 Aug 2020 09:52:20 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="bOr02JwI" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CD7DE2078D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvmarm-bounces@lists.cs.columbia.edu Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 4E9784B8E7; Thu, 13 Aug 2020 05:52:20 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Authentication-Results: mm01.cs.columbia.edu (amavisd-new); dkim=softfail (fail, message has been altered) header.i=@kernel.org Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id y0G65sCufUBM; Thu, 13 Aug 2020 05:52:19 -0400 (EDT) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 328224B8F5; Thu, 13 Aug 2020 05:52:19 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 41E2F4B8E7 for ; Thu, 13 Aug 2020 05:52:18 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id Sg8NhE9qK9A6 for ; Thu, 13 Aug 2020 05:52:16 -0400 (EDT) Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by mm01.cs.columbia.edu (Postfix) with ESMTPS id 9F56B4B8BA for ; Thu, 13 Aug 2020 05:52:16 -0400 (EDT) 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 8007E2074D; Thu, 13 Aug 2020 09:52:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1597312335; bh=giRbKmVntSvhX0nekqsc2yIFsJh4IIaldkUru1ENsns=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=bOr02JwIBVdUa8K5PnV6OvNBmNQeTBwVv2R41g7G+wFneiPUkpse7fn9GEhD697Fb YyK6vUOhi3h4jH+YifCYKpUu675MuCOZpLy8yZTYvSqwE/a9KN/opFWXYG7VkZWE6O llMX/Np1Wl4h5mYcY0gbk4k4uXrMY71HQyVag5HE= 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 1k69u9-001kVc-Mc; Thu, 13 Aug 2020 10:52:13 +0100 MIME-Version: 1.0 Date: Thu, 13 Aug 2020 10:52:13 +0100 From: Marc Zyngier To: Peng Liang Subject: Re: [RFC 3/4] kvm: arm64: make ID registers configurable In-Reply-To: <20200813060517.2360048-4-liangpeng10@huawei.com> References: <20200813060517.2360048-1-liangpeng10@huawei.com> <20200813060517.2360048-4-liangpeng10@huawei.com> User-Agent: Roundcube Webmail/1.4.5 Message-ID: <73a299dd67053f094498dd98a65fbc71@kernel.org> X-Sender: maz@kernel.org X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: liangpeng10@huawei.com, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, will@kernel.org, zhang.zhanghailiang@huawei.com, xiexiangyou@huawei.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Cc: will@kernel.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, zhang.zhanghailiang@huawei.com 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 2020-08-13 07:05, Peng Liang wrote: > It's time to make ID registers configurable. When userspace (but not > guest) want to set the values of ID registers, save the value in > kvm_arch_vcpu so that guest can read the modified values. > > Signed-off-by: zhanghailiang > Signed-off-by: Peng Liang > --- > arch/arm64/kvm/sys_regs.c | 23 ++++++++++++++++------- > 1 file changed, 16 insertions(+), 7 deletions(-) > > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c > index 776c2757a01e..f98635489966 100644 > --- a/arch/arm64/kvm/sys_regs.c > +++ b/arch/arm64/kvm/sys_regs.c > @@ -1111,6 +1111,14 @@ static u64 kvm_get_id_reg(struct kvm_vcpu *vcpu, > u64 id) > return ri->sys_val; > } > > +static void kvm_set_id_reg(struct kvm_vcpu *vcpu, u64 id, u64 value) > +{ > + struct id_reg_info *ri = kvm_id_reg(vcpu, id); > + > + BUG_ON(!ri); > + ri->sys_val = value; > +} > + > /* Read a sanitised cpufeature ID register by sys_reg_desc */ > static u64 read_id_reg(struct kvm_vcpu *vcpu, > struct sys_reg_desc const *r, bool raz) > @@ -1252,10 +1260,6 @@ static int set_id_aa64zfr0_el1(struct kvm_vcpu > *vcpu, > > /* > * cpufeature ID register user accessors > - * > - * For now, these registers are immutable for userspace, so no values > - * are stored, and for set_id_reg() we don't allow the effective value > - * to be changed. > */ > static int __get_id_reg(struct kvm_vcpu *vcpu, > const struct sys_reg_desc *rd, void __user *uaddr, > @@ -1279,9 +1283,14 @@ static int __set_id_reg(struct kvm_vcpu *vcpu, > if (err) > return err; > > - /* This is what we mean by invariant: you can't change it. */ > - if (val != read_id_reg(vcpu, rd, raz)) > - return -EINVAL; > + if (raz) { > + if (val != read_id_reg(vcpu, rd, raz)) > + return -EINVAL; > + } else { > + u32 reg_id = sys_reg((u32)rd->Op0, (u32)rd->Op1, (u32)rd->CRn, > + (u32)rd->CRm, (u32)rd->Op2); > + kvm_set_id_reg(vcpu, reg_id, val); > + } > > return 0; > } This cannot work. If userspace can override an idreg, it cannot conflict with anything the HW is capable of. It also cannot conflict with features that the host doesn't want to expose to the guest. Another thing is that you now have features that do not match the MIDR (you can describe an A57 with SVE, for example). This will trigger issues in guests, as the combination isn't expected. And then there is the eternal story about errata workarounds. If you can override the ID regs, how can the guest mitigate errata that you are now hiding from it? 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=-10.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 75341C433DF for ; Thu, 13 Aug 2020 09:52:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4C38020791 for ; Thu, 13 Aug 2020 09:52:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1597312337; bh=giRbKmVntSvhX0nekqsc2yIFsJh4IIaldkUru1ENsns=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=UAkvlfZBh5r3/buvFz5AhX7noXbbKeIjcCulgdqJ3QZAitkEhCbyl8jLYBT7FlBiD LaK/0Fh5zEkgv6NqR/DVMQYz0fco/46NT1FY67IlowfTzqPJLCnOicnAdBPM5ZKCbu pJGxGyaEkXgc0Y44hlsY4/YXMKmD6309ipe6xKEw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726167AbgHMJwQ (ORCPT ); Thu, 13 Aug 2020 05:52:16 -0400 Received: from mail.kernel.org ([198.145.29.99]:34810 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726048AbgHMJwQ (ORCPT ); Thu, 13 Aug 2020 05:52:16 -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 8007E2074D; Thu, 13 Aug 2020 09:52:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1597312335; bh=giRbKmVntSvhX0nekqsc2yIFsJh4IIaldkUru1ENsns=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=bOr02JwIBVdUa8K5PnV6OvNBmNQeTBwVv2R41g7G+wFneiPUkpse7fn9GEhD697Fb YyK6vUOhi3h4jH+YifCYKpUu675MuCOZpLy8yZTYvSqwE/a9KN/opFWXYG7VkZWE6O llMX/Np1Wl4h5mYcY0gbk4k4uXrMY71HQyVag5HE= 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 1k69u9-001kVc-Mc; Thu, 13 Aug 2020 10:52:13 +0100 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Thu, 13 Aug 2020 10:52:13 +0100 From: Marc Zyngier To: Peng Liang Cc: kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, will@kernel.org, zhang.zhanghailiang@huawei.com, xiexiangyou@huawei.com Subject: Re: [RFC 3/4] kvm: arm64: make ID registers configurable In-Reply-To: <20200813060517.2360048-4-liangpeng10@huawei.com> References: <20200813060517.2360048-1-liangpeng10@huawei.com> <20200813060517.2360048-4-liangpeng10@huawei.com> User-Agent: Roundcube Webmail/1.4.5 Message-ID: <73a299dd67053f094498dd98a65fbc71@kernel.org> X-Sender: maz@kernel.org X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: liangpeng10@huawei.com, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, will@kernel.org, zhang.zhanghailiang@huawei.com, xiexiangyou@huawei.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 2020-08-13 07:05, Peng Liang wrote: > It's time to make ID registers configurable. When userspace (but not > guest) want to set the values of ID registers, save the value in > kvm_arch_vcpu so that guest can read the modified values. > > Signed-off-by: zhanghailiang > Signed-off-by: Peng Liang > --- > arch/arm64/kvm/sys_regs.c | 23 ++++++++++++++++------- > 1 file changed, 16 insertions(+), 7 deletions(-) > > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c > index 776c2757a01e..f98635489966 100644 > --- a/arch/arm64/kvm/sys_regs.c > +++ b/arch/arm64/kvm/sys_regs.c > @@ -1111,6 +1111,14 @@ static u64 kvm_get_id_reg(struct kvm_vcpu *vcpu, > u64 id) > return ri->sys_val; > } > > +static void kvm_set_id_reg(struct kvm_vcpu *vcpu, u64 id, u64 value) > +{ > + struct id_reg_info *ri = kvm_id_reg(vcpu, id); > + > + BUG_ON(!ri); > + ri->sys_val = value; > +} > + > /* Read a sanitised cpufeature ID register by sys_reg_desc */ > static u64 read_id_reg(struct kvm_vcpu *vcpu, > struct sys_reg_desc const *r, bool raz) > @@ -1252,10 +1260,6 @@ static int set_id_aa64zfr0_el1(struct kvm_vcpu > *vcpu, > > /* > * cpufeature ID register user accessors > - * > - * For now, these registers are immutable for userspace, so no values > - * are stored, and for set_id_reg() we don't allow the effective value > - * to be changed. > */ > static int __get_id_reg(struct kvm_vcpu *vcpu, > const struct sys_reg_desc *rd, void __user *uaddr, > @@ -1279,9 +1283,14 @@ static int __set_id_reg(struct kvm_vcpu *vcpu, > if (err) > return err; > > - /* This is what we mean by invariant: you can't change it. */ > - if (val != read_id_reg(vcpu, rd, raz)) > - return -EINVAL; > + if (raz) { > + if (val != read_id_reg(vcpu, rd, raz)) > + return -EINVAL; > + } else { > + u32 reg_id = sys_reg((u32)rd->Op0, (u32)rd->Op1, (u32)rd->CRn, > + (u32)rd->CRm, (u32)rd->Op2); > + kvm_set_id_reg(vcpu, reg_id, val); > + } > > return 0; > } This cannot work. If userspace can override an idreg, it cannot conflict with anything the HW is capable of. It also cannot conflict with features that the host doesn't want to expose to the guest. Another thing is that you now have features that do not match the MIDR (you can describe an A57 with SVE, for example). This will trigger issues in guests, as the combination isn't expected. And then there is the eternal story about errata workarounds. If you can override the ID regs, how can the guest mitigate errata that you are now hiding from it? Thanks, M. -- Jazz is not dead. It just smells funny...