[{"id":1768592,"web_url":"http://patchwork.ozlabs.org/comment/1768592/","msgid":"<87377p9zja.fsf@linaro.org>","list_archive_url":null,"date":"2017-09-14T13:32:09","subject":"Re: [PATCH v2 24/28] arm64/sve: KVM: Hide SVE from CPU features\n\texposed to guests","submitter":{"id":39532,"url":"http://patchwork.ozlabs.org/api/people/39532/","name":"Alex Bennée","email":"alex.bennee@linaro.org"},"content":"Dave Martin writes:\n\n> KVM guests cannot currently use SVE, because SVE is always\n> configured to trap to EL2.\n>\n> However, a guest that sees SVE reported as present in\n> ID_AA64PFR0_EL1 may legitimately expect that SVE works and try to\n> use it. Instead of working, the guest will receive an injected\n> undef exception, which may cause the guest to oops or go into a\n> spin.\n>\n> To avoid misleading the guest into believing that SVE will work,\n> this patch masks out the SVE field from ID_AA64PFR0_EL1 when a\n> guest attempts to read this register. No support is explicitly\n> added for ID_AA64ZFR0_EL1 either, so that is still emulated as\n> reading as zero, which is consistent with SVE not being\n> implemented.\n>\n> This is a temporary measure, and will be removed in a later series\n> when full KVM support for SVE is implemented.\n>\n> Signed-off-by: Dave Martin \n> Cc: Marc Zyngier \n\nReviewed-by: Alex Bennée \n\n>\n> ---\n>\n> Changes since v1\n> ----------------\n>\n> Requested by Marc Zyngier:\n>\n> * Use pr_err() instead inventing \"kvm_info_once\" ad-hoc.\n> ---\n> arch/arm64/kvm/sys_regs.c | 12 +++++++++++-\n> 1 file changed, 11 insertions(+), 1 deletion(-)\n>\n> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c\n> index b1f7552..a0ee9b0 100644\n> --- a/arch/arm64/kvm/sys_regs.c\n> +++ b/arch/arm64/kvm/sys_regs.c\n> @@ -23,6 +23,7 @@\n> #include \n> #include \n> #include \n> +#include \n> #include \n>\n> #include \n> @@ -897,8 +898,17 @@ static u64 read_id_reg(struct sys_reg_desc const *r, bool raz)\n> {\n> \tu32 id = sys_reg((u32)r->Op0, (u32)r->Op1,\n> \t\t\t (u32)r->CRn, (u32)r->CRm, (u32)r->Op2);\n> +\tu64 val = raz ? 0 : read_sanitised_ftr_reg(id);\n>\n> -\treturn raz ? 0 : read_sanitised_ftr_reg(id);\n> +\tif (id == SYS_ID_AA64PFR0_EL1) {\n> +\t\tif (val & (0xfUL << ID_AA64PFR0_SVE_SHIFT))\n> +\t\t\tpr_err_once(\"kvm [%i]: SVE unsupported for guests, suppressing\\n\",\n> +\t\t\t\t task_pid_nr(current));\n> +\n> +\t\tval &= ~(0xfUL << ID_AA64PFR0_SVE_SHIFT);\n> +\t}\n> +\n> +\treturn val;\n> }\n>\n> /* cpufeature ID register access trap handlers */\n\n\n--\nAlex Bennée","headers":{"Return-Path":"","X-Original-To":"incoming@patchwork.ozlabs.org","Delivered-To":["patchwork-incoming@bilbo.ozlabs.org","mailing list libc-alpha@sourceware.org"],"Authentication-Results":["ozlabs.org;\n\tspf=pass (mailfrom) smtp.mailfrom=sourceware.org\n\t(client-ip=209.132.180.131; helo=sourceware.org;\n\tenvelope-from=libc-alpha-return-84617-incoming=patchwork.ozlabs.org@sourceware.org;\n\treceiver=)","ozlabs.org; dkim=pass (1024-bit key;\n\tsecure) header.d=sourceware.org header.i=@sourceware.org\n\theader.b=\"OUCpTEvo\"; dkim-atps=neutral","sourceware.org; auth=none"],"Received":["from sourceware.org (server1.sourceware.org [209.132.180.131])\n\t(using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256\n\tbits)) (No client certificate requested)\n\tby ozlabs.org (Postfix) with ESMTPS id 3xtKFz12wXz9s81\n\tfor ;\n\tThu, 14 Sep 2017 23:32:22 +1000 (AEST)","(qmail 99828 invoked by alias); 14 Sep 2017 13:32:15 -0000","(qmail 99794 invoked by uid 89); 14 Sep 2017 13:32:14 -0000"],"DomainKey-Signature":"a=rsa-sha1; c=nofws; d=sourceware.org; h=list-id\n\t:list-unsubscribe:list-subscribe:list-archive:list-post\n\t:list-help:sender:references:from:to:cc:subject:in-reply-to:date\n\t:message-id:mime-version:content-type:content-transfer-encoding;\n\tq=dns; s=default; b=aoktwE5exQgaZpBvwH0ltxQuJtqHOra26ZM58vTCmiQ\n\t0nzIV91Fiy6+WVFTL7soCM+fvFzMR49QmdDoLr8YN+4OSXQAnLcUraB2Zrh7Joo5\n\t5poPbciXNbvT56Np/JwXHzyMAqvGtpKit7MpbSEvBFweIrbyoaBCrdnM6Loi8J90\n\t=","DKIM-Signature":"v=1; a=rsa-sha1; c=relaxed; d=sourceware.org; h=list-id\n\t:list-unsubscribe:list-subscribe:list-archive:list-post\n\t:list-help:sender:references:from:to:cc:subject:in-reply-to:date\n\t:message-id:mime-version:content-type:content-transfer-encoding;\n\ts=default; bh=alq0xbIas2lpJ9/okzUHkoghZuo=; b=OUCpTEvoXkuDUOWAi\n\tpsmhBJg41k6AHz9rfXFaglHxpS8VOO7mEnfhet079bchxKZVdpTOvyZXtUmVCVsy\n\tj2jXMl81yMR1BKYBdfJIVbtshlN+gyzxPXdb1EiP99LZdDq6IgDubxiDN+GK5gtJ\n\tTNc+Mri1KCSK9JnAAGMS455HEY=","Mailing-List":"contact libc-alpha-help@sourceware.org; run by ezmlm","Precedence":"bulk","List-Id":"","List-Unsubscribe":"","List-Subscribe":"","List-Archive":"","List-Post":"","List-Help":",\n\t","Sender":"libc-alpha-owner@sourceware.org","X-Virus-Found":"No","X-Spam-SWARE-Status":"No, score=-26.1 required=5.0 tests=AWL, BAYES_00,\n\tGIT_PATCH_0, GIT_PATCH_1, GIT_PATCH_2, GIT_PATCH_3,\n\tRCVD_IN_DNSWL_NONE, RCVD_IN_SORBS_SPAM,\n\tSPF_PASS autolearn=ham version=3.3.2 spammy=spin","X-HELO":"mail-wr0-f178.google.com","X-Google-DKIM-Signature":"v=1; a=rsa-sha256; c=relaxed/relaxed;\n\td=1e100.net; s=20161025;\n\th=x-gm-message-state:references:user-agent:from:to:cc:subject\n\t:in-reply-to:date:message-id:mime-version:content-transfer-encoding; \n\tbh=rmNW3P2g2GcItczNrUMqk7V7dI0HdJcCItpjEaBRAMk=;\n\tb=pke2p70Kv64POBZXVOw3iwTpBMmkBvwA48GT9vgPBTxzthvF/dLwGy2pXoMNA7XjE1\n\tGFlYssyKJQnKkX6E+gjGs4aanTE5iDJUSFZTSSuqCq00PT43LFwsqLDfnT1tAnWCkfyH\n\ttPGNtOoTBRCKNjk+YO1JqfOX3DvSrwvLhxxADcRqjCNAhXf2iOrYv7C8s6crXQdWlxAh\n\tirsCk/RpmnYJ3NjbDhbrtvQFc+YLZBSKkF7iMPqG3KNTzc0ZTXoQ9PMpAGYjGak6Y1P6\n\tejpODQpGHq5UWd3QgcuouGyzF0vlV4ZPxSbZPOPRMBtLuz1A4lAMFSDOJxLlFk49oR37\n\t6gUg==","X-Gm-Message-State":"AHPjjUi0czeghkn4DQv6O6/C4dgjkTLtQSa7UaxTKaTk6aP6dzc9pB6R\n\tWAcGpVKngEJ4JEeF","X-Google-Smtp-Source":"ADKCNb4tgfz89IVHnr3CP+X+i5lZ6wn0rtsXtK18YX5cz3FeZkRGyJwtVvX3B1F0MBC+ea2d4YNEVA==","X-Received":"by 10.223.196.11 with SMTP id v11mr17294884wrf.21.1505395931139; \n\tThu, 14 Sep 2017 06:32:11 -0700 (PDT)","References":"<1504198860-12951-1-git-send-email-Dave.Martin@arm.com>\n\t<1504198860-12951-25-git-send-email-Dave.Martin@arm.com>","User-agent":"mu4e 0.9.19; emacs 25.2.50.3","From":"Alex =?utf-8?q?Benn=C3=A9e?= ","To":"Dave Martin ","Cc":"linux-arm-kernel@lists.infradead.org,\n\tCatalin Marinas ,\n\tWill Deacon ,\n\tArd Biesheuvel ,\n\tSzabolcs Nagy ,\n\tRichard Sandiford ,\n\tkvmarm@lists.cs.columbia.edu, libc-alpha@sourceware.org,\n\tlinux-arch@vger.kernel.org,\n\tChristoffer Dall ,\n\tMarc Zyngier ","Subject":"Re: [PATCH v2 24/28] arm64/sve: KVM: Hide SVE from CPU features\n\texposed to guests","In-reply-to":"<1504198860-12951-25-git-send-email-Dave.Martin@arm.com>","Date":"Thu, 14 Sep 2017 14:32:09 +0100","Message-ID":"<87377p9zja.fsf@linaro.org>","MIME-Version":"1.0","Content-Type":"text/plain; charset=utf-8","Content-Transfer-Encoding":"8bit"}}]