From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AH8x225jai/5yHAiPaI6W6kt6ezCNthYdFJ5R9MyRFFFkqgO0B36IOI7efmh5JkualnkyJINk5/D ARC-Seal: i=1; a=rsa-sha256; t=1517176062; cv=none; d=google.com; s=arc-20160816; b=u/54V1PiAmBIHrga7D23DBlpVUrq0OpPDCoAGzs1fRDoIhuQXj5LKx5ymGUKhoafTr tF4z3akUk3G54HfPkFdjSURSqNUTB//Z3jC7vPcbtS+l6gXt+31tt4jCqjN/VvHJ6DSq imxqhes8KZS/iVWEw7rO65M9xlkn8G9X8r4aac4NOiXRWKfDYsGPYiAuM3s8tLmjCKIf pwl/8Qaa1dgiCgsQ8EwMDUsZjXjNoz8eRKXkR73E41p6SFCOx7gRyON3a6xdZFP1TlII ZsEwfRdIlZCp18KD+qImj1hcHojVubXiiG8yrHpenPnEqdPCLy1wMIH3W1TT+a1SMKH2 zLzQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=importance:content-transfer-encoding:mime-version:user-agent:cc:to :from:subject:date:references:in-reply-to:message-id:dkim-signature :arc-authentication-results; bh=JDJWHKoxzqQ7x7QXSXsXQV5fUQfCF3qgd4h5u/9doB8=; b=OOETgo17oceSQMBxr7BTveKTMqIutJ+lAojQ2k3WiWW2aBAXftscfMmRwLSvvv6Vm+ xCTWmNQFsxseUGwHPoOsPTfUITnanWxCwmxw6KFtmFCFlkl9r+V+K9RKNo0pS3y/sAsw o7E8K8J4Vf39wSCQMOlYFRJtCvtvyEtb8wSVbOxZPE0vFwbKTLTO5D7/ZHCLDvByJnhR SCrlpCSbRZbvqLjIeE/nz3DxNb9L58Ln5526765rKFckwYxrPQuo5mDEwZiRqgkh2iJ8 0lUDmA1bMAQMfb2THVSUWWmsLjKQlpOGoEipm0yLhkC10AedDZotPJAmcGd9Sv75Sm/n Vy2g== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@infradead.org header.s=twosheds.20170209 header.b=rBhbOiIU; spf=pass (google.com: best guess record for domain of batv+bcac6755cd2ccc117aa4+5271+infradead.org+dwmw2@twosheds.srs.infradead.org designates 90.155.92.209 as permitted sender) smtp.mailfrom=BATV+bcac6755cd2ccc117aa4+5271+infradead.org+dwmw2@twosheds.srs.infradead.org Authentication-Results: mx.google.com; dkim=pass header.i=@infradead.org header.s=twosheds.20170209 header.b=rBhbOiIU; spf=pass (google.com: best guess record for domain of batv+bcac6755cd2ccc117aa4+5271+infradead.org+dwmw2@twosheds.srs.infradead.org designates 90.155.92.209 as permitted sender) smtp.mailfrom=BATV+bcac6755cd2ccc117aa4+5271+infradead.org+dwmw2@twosheds.srs.infradead.org Message-ID: <5facc2ddb1d59bcc17837977eb495b57.squirrel@twosheds.infradead.org> In-Reply-To: <0575AF4FD06DD142AD198903C74E1CC87A602447@ORSMSX103.amr.corp.intel.com> References: <1517167750-23485-1-git-send-email-karahmed@amazon.de> <4DCAF18F-C86A-4CBC-A9CC-CC01BF63313F@oracle.com> <86F5D9C0-7B11-448D-954F-D2EF6CBE80EC@amacapital.net> <1517172296.6624.84.camel@infradead.org> <0575AF4FD06DD142AD198903C74E1CC87A602447@ORSMSX103.amr.corp.intel.com> Date: Sun, 28 Jan 2018 21:47:28 -0000 Subject: RE: [PATCH] x86: vmx: Allow direct access to MSR_IA32_SPEC_CTRL From: "David Woodhouse" To: "Van De Ven, Arjan" Cc: "David Woodhouse" , "Andy Lutomirski" , "Konrad Rzeszutek Wilk" , "KarimAllah Ahmed" , "kvm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "Mallick, Asit K" , "Hansen, Dave" , "Andi Kleen" , "Andrea Arcangeli" , "Linus Torvalds" , "Tim Chen" , "Thomas Gleixner" , "Williams, Dan J" , "Nakajima, Jun" , "Paolo Bonzini" , "Greg KH" , "Andy Lutomirski" , "Raj, Ashok" , "daniel.kiper@oracle.com" User-Agent: SquirrelMail/1.4.22-21.fc27 MIME-Version: 1.0 Content-Type: text/plain;charset=utf-8 Content-Transfer-Encoding: 8bit X-Priority: 3 (Normal) Importance: Normal X-SRS-Rewrite: SMTP reverse-path rewritten from by twosheds.infradead.org. See http://www.infradead.org/rpr.html X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1590865729989295970?= X-GMAIL-MSGID: =?utf-8?q?1590874406617473788?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: >> >> On Sun, 2018-01-28 at 12:40 -0800, Andy Lutomirski wrote: >> > >> > Do you mean that the host would intercept the guest WRMSR and do >> > WRMSR itself?  I would suggest that doing so is inconsistent with the >> > docs.  As specified, doing WRMSR to write 1 to IBRS does *not* >> > protect the guest. >> >> I believe it does. Guest kernel is protected from any guest userspace >> predictions learned before IBRS was last set to 1 in *any* mode, >> including host. > > the specification requires you to write a 1 on each transition to higher > privilege. Right. Andy's concern was about VMX non-root (i.e. guest) ring 0 attempting to write IBRS but it's trapped and actually happens in the host. As long as it *remains* set when the host re-enters the vCPU that should be fine. -- dwmw2