From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AH8x225L6Ec8DY+ngo2eSpcPgXSHP/NfOOm/feEb0OqFOlzaNyqeAjiH/z4+ENYS1jpz4B00zffI ARC-Seal: i=1; a=rsa-sha256; t=1517570897; cv=none; d=google.com; s=arc-20160816; b=fmdhjP4sCvlKdF/D/Pg5b2AfQHpXRTPhA4MwIVGb8HjxzvNRyXR9U/fyYviLa5+QDO CEt47/za1uP64QYvWWgA26bygf699cDKr0zSgMLb+KxkVWkvUo1x3nsrvs7kVNNrtKAd kK56MuUAMEHrrdB/j7G3Qw8E23ew/LZCOKB/rWv4mVE3lixswXMTpqJ/E/gsaEgALtNA 9W2Pv+GPpe8zGwZOScHjaaS7phD0RtOifQYtRcXR1jItjCdva7Hrwe7cJ/cciTWXmTjd zQOx+yL5wE50VHzm/Bqun5yjvQtcUMbc4/ubgklI+a+A/JgSt9SIVk9OELcTyIS/Mxzm MaMA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=mime-version:date:face:references:in-reply-to:cc:to:from:subject :message-id:dkim-signature:arc-authentication-results; bh=tnzj0RvukCXkpjQx88hQwqiIGtlkv/+dopqjmRbitoI=; b=hCW2EtM1g8wDulRHAH1UkjbiC3mm+qOsmFa5N4VW2wFpm8Gcws08VKThQakyq3IZrt 7oxB8puKBxq+7EGhCiCev3FpNPwf/MpAInMkReO8TJ1JYQD91e2DeeiYlLZsBMWpO7ei Dx0n5HYpv7lNxEIykw2XuARyclQbpS2vinVS+HGyT2V1T8H8ZDbNBWMir/tP2bzGY7dJ vF6N+1PflkK5uZMWwaswkEKhYEo4K+KxxMEoufmI+eXjfUpCvtayWWta3YFJklWTLA37 AIQMVJbrRnZmkCD9fi18xsQg9DDRG+WYbIg0piqb9EEC9/HL72QPNbfnei9EiGwTDcY0 745A== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@infradead.org header.s=twosheds.20170209 header.b=pBaohZkq; spf=pass (google.com: best guess record for domain of batv+fa3758ec04dcdc472965+5276+infradead.org+dwmw2@twosheds.srs.infradead.org designates 90.155.92.209 as permitted sender) smtp.mailfrom=BATV+fa3758ec04dcdc472965+5276+infradead.org+dwmw2@twosheds.srs.infradead.org Authentication-Results: mx.google.com; dkim=pass header.i=@infradead.org header.s=twosheds.20170209 header.b=pBaohZkq; spf=pass (google.com: best guess record for domain of batv+fa3758ec04dcdc472965+5276+infradead.org+dwmw2@twosheds.srs.infradead.org designates 90.155.92.209 as permitted sender) smtp.mailfrom=BATV+fa3758ec04dcdc472965+5276+infradead.org+dwmw2@twosheds.srs.infradead.org Message-ID: <1517570852.31953.13.camel@infradead.org> Subject: Re: [PATCH v6 4/5] KVM: VMX: Allow direct access to MSR_IA32_SPEC_CTRL From: David Woodhouse To: KarimAllah Ahmed , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org Cc: Asit Mallick , Arjan Van De Ven , Dave Hansen , Andi Kleen , Andrea Arcangeli , Linus Torvalds , Tim Chen , Thomas Gleixner , Dan Williams , Jun Nakajima , Paolo Bonzini , Greg KH , Andy Lutomirski , Ashok Raj In-Reply-To: <1517522386-18410-5-git-send-email-karahmed@amazon.de> References: <1517522386-18410-1-git-send-email-karahmed@amazon.de> <1517522386-18410-5-git-send-email-karahmed@amazon.de> Face: 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 Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-DLZHqgCYNs+NBdhjqleo" Date: Fri, 02 Feb 2018 11:27:32 +0000 Mime-Version: 1.0 X-Mailer: Evolution 3.18.5.2-0ubuntu3.2 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?1591237580461918240?= X-GMAIL-MSGID: =?utf-8?q?1591288421657914047?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: --=-DLZHqgCYNs+NBdhjqleo Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, 2018-02-01 at 22:59 +0100, KarimAllah Ahmed wrote: > [ Based on a patch from Ashok Raj ] >=20 > Add direct access to MSR_IA32_SPEC_CTRL for guests. This is needed for > guests that will only mitigate Spectre V2 through IBRS+IBPB and will not > be using a retpoline+IBPB based approach. >=20 > To avoid the overhead of saving and restoring the MSR_IA32_SPEC_CTRL for > guests that do not actually use the MSR, only start saving and restoring > when a non-zero is written to it. >=20 > No attempt is made to handle STIBP here, intentionally. Filtering STIBP > may be added in a future patch, which may require trapping all writes > if we don't want to pass it through directly to the guest. >=20 > [dwmw2: Clean up CPUID bits, save/restore manually, handle reset] >=20 > Cc: Asit Mallick > Cc: Arjan Van De Ven > Cc: Dave Hansen > Cc: Andi Kleen > Cc: Andrea Arcangeli > Cc: Linus Torvalds > Cc: Tim Chen > Cc: Thomas Gleixner > Cc: Dan Williams > Cc: Jun Nakajima > Cc: Paolo Bonzini > Cc: David Woodhouse > Cc: Greg KH > Cc: Andy Lutomirski > Cc: Ashok Raj > Signed-off-by: KarimAllah Ahmed > Signed-off-by: David Woodhouse > --- > v6: > - got rid of save_spec_ctrl_on_exit > - introduce msr_write_intercepted > v5: > - Also check for X86_FEATURE_SPEC_CTRL for the msr reads/writes > v4: > - Add IBRS to kvm_cpuid_8000_0008_ebx_x86_features > - Handling nested guests > v3: > - Save/restore manually > - Fix CPUID handling > - Fix a copy & paste error in the name of SPEC_CTRL MSR in > =C2=A0 disable_intercept. > - support !cpu_has_vmx_msr_bitmap() > v2: > - remove 'host_spec_ctrl' in favor of only a comment (dwmw@). > - special case writing '0' in SPEC_CTRL to avoid confusing live-migration > =C2=A0 when the instance never used the MSR (dwmw@). > - depend on X86_FEATURE_IBRS instead of X86_FEATURE_SPEC_CTRL (dwmw@). > - add MSR_IA32_SPEC_CTRL to the list of MSRs to save (dropped it by accid= ent). This looks very good to me now, and the comments are helpful. Thank you for your persistence with getting the details right. If we make the SVM one look like this, as you mentioned, I think we ought finally be ready to merge it. 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Ashok Raj To: KarimAllah Ahmed , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org Return-path: Received: from twosheds.infradead.org ([90.155.92.209]:38366 "EHLO twosheds.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751416AbeBBL1q (ORCPT ); Fri, 2 Feb 2018 06:27:46 -0500 In-Reply-To: <1517522386-18410-5-git-send-email-karahmed@amazon.de> Sender: kvm-owner@vger.kernel.org List-ID: --=-DLZHqgCYNs+NBdhjqleo Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, 2018-02-01 at 22:59 +0100, KarimAllah Ahmed wrote: > [ Based on a patch from Ashok Raj ] >=20 > Add direct access to MSR_IA32_SPEC_CTRL for guests. This is needed for > guests that will only mitigate Spectre V2 through IBRS+IBPB and will not > be using a retpoline+IBPB based approach. >=20 > To avoid the overhead of saving and restoring the MSR_IA32_SPEC_CTRL for > guests that do not actually use the MSR, only start saving and restoring > when a non-zero is written to it. >=20 > No attempt is made to handle STIBP here, intentionally. Filtering STIBP > may be added in a future patch, which may require trapping all writes > if we don't want to pass it through directly to the guest. >=20 > [dwmw2: Clean up CPUID bits, save/restore manually, handle reset] >=20 > Cc: Asit Mallick > Cc: Arjan Van De Ven > Cc: Dave Hansen > Cc: Andi Kleen > Cc: Andrea Arcangeli > Cc: Linus Torvalds > Cc: Tim Chen > Cc: Thomas Gleixner > Cc: Dan Williams > Cc: Jun Nakajima > Cc: Paolo Bonzini > Cc: David Woodhouse > Cc: Greg KH > Cc: Andy Lutomirski > Cc: Ashok Raj > Signed-off-by: KarimAllah Ahmed > Signed-off-by: David Woodhouse > --- > v6: > - got rid of save_spec_ctrl_on_exit > - introduce msr_write_intercepted > v5: > - Also check for X86_FEATURE_SPEC_CTRL for the msr reads/writes > v4: > - Add IBRS to kvm_cpuid_8000_0008_ebx_x86_features > - Handling nested guests > v3: > - Save/restore manually > - Fix CPUID handling > - Fix a copy & paste error in the name of SPEC_CTRL MSR in > =C2=A0 disable_intercept. > - support !cpu_has_vmx_msr_bitmap() > v2: > - remove 'host_spec_ctrl' in favor of only a comment (dwmw@). > - special case writing '0' in SPEC_CTRL to avoid confusing live-migration > =C2=A0 when the instance never used the MSR (dwmw@). > - depend on X86_FEATURE_IBRS instead of X86_FEATURE_SPEC_CTRL (dwmw@). > - add MSR_IA32_SPEC_CTRL to the list of MSRs to save (dropped it by accid= ent). This looks very good to me now, and the comments are helpful. Thank you for your persistence with getting the details right. If we make the SVM one look like this, as you mentioned, I think we ought finally be ready to merge it. 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