From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AB8JxZpXruww/l7zj2EwBrMWfqXq7Yrj6Xb+zRrQpuAk0JDdJcuDD0ppzwoysXB0dAA76M/W1NFu ARC-Seal: i=1; a=rsa-sha256; t=1526937306; cv=none; d=google.com; s=arc-20160816; b=mB86cxKbYGEvHbdGzbWJqwazklXdYDXo7JWPhxn3yxl59xtxS4kKEtC2a3S6wo0ejy mxZXjm9Osac6qbgfSl8DJW/bRI4BwQuEklv9NUFiVAFSvDXDAxjsQo8b6FD9XH1OHg1A ZIAXFzicoHI2AvSIEv09EeEPaat5Dag2MlgogDtMswr36HSH8aW4uTFIh4K40QeB/D9i dp2lvnIZenEkh8GYFrELCvutj/530XDD2lfxPALHbp/1NedBXTh10NSw3+DRjesYCIq1 iBwITPLc9eGUv1HGv686RdaMuoQTDgjWU05AO3dHtaAnscAmVUlkcY9qVUqPx4DJBF0i t3eg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=mime-version:user-agent:references:in-reply-to:message-id:date :subject:cc:to:from:dkim-signature:arc-authentication-results; bh=yvrbbGee7JkF8TooSs8rQMj7c2ugwWaoldxP73KWorE=; b=rZihh0DmEU7vDOUNpI04wkdsM8jpklSzERI1+A0iOkIcwg9YdzLkjgnG3XgSDQuisO 5k5Q3KcEFYZHrpaEaUztWeZtsYITpZxncsI3ITJJYCfBPMAIEo6sI2NHLpuveVJgMz5r NQ5tdZaGq9t3PAgz/5MM19MNGPQuJ5jv6Pd7a21ifXSxx3yuGd7/18VDYps9qNWjf20D g3QSUehzAoUkCUPgcwiMIC1MZcyhb4xDsI2VhGAYwHutp5zB5zPdjha6b2w/cNmPVF45 0rMnlxfv4skHSUmuEhractBYQmrCOYlrU944kKni5w8nbw1UuulFxgr3WKMk6w1/e2u8 FyJg== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@kernel.org header.s=default header.b=sFbTZIhV; spf=pass (google.com: domain of srs0=nia/=ii=linuxfoundation.org=gregkh@kernel.org designates 198.145.29.99 as permitted sender) smtp.mailfrom=SRS0=nia/=II=linuxfoundation.org=gregkh@kernel.org Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=default header.b=sFbTZIhV; spf=pass (google.com: domain of srs0=nia/=ii=linuxfoundation.org=gregkh@kernel.org designates 198.145.29.99 as permitted sender) smtp.mailfrom=SRS0=nia/=II=linuxfoundation.org=gregkh@kernel.org From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Juergen Gross , Boris Ostrovsky , Thomas Gleixner , David Woodhouse Subject: [PATCH 4.9 34/87] x86/amd: dont set X86_BUG_SYSRET_SS_ATTRS when running under Xen Date: Mon, 21 May 2018 23:11:10 +0200 Message-Id: <20180521210423.609407739@linuxfoundation.org> X-Mailer: git-send-email 2.17.0 In-Reply-To: <20180521210420.222671977@linuxfoundation.org> References: <20180521210420.222671977@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-LABELS: =?utf-8?b?IlxcU2VudCI=?= X-GMAIL-THRID: =?utf-8?q?1601109813034580646?= X-GMAIL-MSGID: =?utf-8?q?1601109813034580646?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ commit def9331a12977770cc6132d79f8e6565871e8e38 upstream When running as Xen pv guest X86_BUG_SYSRET_SS_ATTRS must not be set on AMD cpus. This bug/feature bit is kind of special as it will be used very early when switching threads. Setting the bit and clearing it a little bit later leaves a critical window where things can go wrong. This time window has enlarged a little bit by using setup_clear_cpu_cap() instead of the hypervisor's set_cpu_features callback. It seems this larger window now makes it rather easy to hit the problem. The proper solution is to never set the bit in case of Xen. Signed-off-by: Juergen Gross Reviewed-by: Boris Ostrovsky Acked-by: Thomas Gleixner Signed-off-by: Juergen Gross Signed-off-by: David Woodhouse Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/cpu/amd.c | 5 +++-- arch/x86/xen/enlighten.c | 4 +--- 2 files changed, 4 insertions(+), 5 deletions(-) --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -824,8 +824,9 @@ static void init_amd(struct cpuinfo_x86 if (cpu_has(c, X86_FEATURE_3DNOW) || cpu_has(c, X86_FEATURE_LM)) set_cpu_cap(c, X86_FEATURE_3DNOWPREFETCH); - /* AMD CPUs don't reset SS attributes on SYSRET */ - set_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS); + /* AMD CPUs don't reset SS attributes on SYSRET, Xen does. */ + if (!cpu_has(c, X86_FEATURE_XENPV)) + set_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS); } #ifdef CONFIG_X86_32 --- a/arch/x86/xen/enlighten.c +++ b/arch/x86/xen/enlighten.c @@ -1977,10 +1977,8 @@ EXPORT_SYMBOL_GPL(xen_hvm_need_lapic); static void xen_set_cpu_features(struct cpuinfo_x86 *c) { - if (xen_pv_domain()) { - clear_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS); + if (xen_pv_domain()) set_cpu_cap(c, X86_FEATURE_XENPV); - } } static void xen_pin_vcpu(int cpu)