From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: ARC-Seal: i=1; a=rsa-sha256; t=1517594255; cv=none; d=google.com; s=arc-20160816; b=D0aJYDivUjAa5/JkA5PuiNO191umAFwgf73H+qLNTemtYiOVSLkT/QrM32UMrYrEVS xOykUB1OPnfDuCNx/KhU9behwtz9c/tuGXyvvRSjLrOn9nUvDsKtQ2HsjYaTS2aCWrHi o1tEuVTNGcN4780jpEl2Rc2MHi4NCBkNAj2V+M3RuwnlEGJYJ99IUBnVf+/gHMQlhmnU 9vn9Y9vfM7x61NlrvgSMotlptb32WIS47TYfbizY36fgcL7xeki1gP9sRW61ny3IXWw0 7UJlxEpZ10B1T1fCLj3m5GlUwLJ6VDp3/Wp64440ocIcJziAzWGeLWshKCmHOYA4zZ9Z LjnQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=cc:to:subject:message-id:date:from:references:in-reply-to :mime-version:dkim-signature:arc-authentication-results; bh=uUX8ChOe5auxpLm1SScFHrEGfIYnayqmOeshWRSAoIA=; b=sK7/MyPvfu/vDjOB2BjwIS5k4vVYk2KHl5dfj22eI6O4wjWMddtRZdKXarBQ+H/W1V oMfhnqVQBwVPIGXvGIcSCv72TE8qsq8/fjZeiSFTAXd3gDFwRN3Bynd0gtINxOkMXrIL DdvcgpFV6+w2sIv3KtNANo9JX4yAPnTIRMxytCR5lFNDs5WJGzFQ51a+/kZBczKAeBKr sLB5mfpG9KQ7QzMC7bSVE7CA9/dFehxX0X6swqTX6ucOQNWRP1cIpylWzVds58l6FARA CqSRf7XGUBHynAXVMffWjr+lM5fQ8me4YbcWijIMFVrtV9MxILmkiqSCUKwSZSkHDjvK GjuA== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@google.com header.s=20161025 header.b=liOil1K7; spf=pass (google.com: domain of jmattson@google.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=jmattson@google.com; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=google.com Authentication-Results: mx.google.com; dkim=pass header.i=@google.com header.s=20161025 header.b=liOil1K7; spf=pass (google.com: domain of jmattson@google.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=jmattson@google.com; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=google.com X-Google-Smtp-Source: AH8x2276kEYVnV97n2UpU5/38IaBuIQljanNLyr+/Uw9VBGVxumNi0HUpV5yzucE6cKBBQjX6iOJJknWgJHgmWiI9Ys= MIME-Version: 1.0 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> From: Jim Mattson Date: Fri, 2 Feb 2018 09:57:34 -0800 Message-ID: Subject: Re: [PATCH v6 4/5] KVM: VMX: Allow direct access to MSR_IA32_SPEC_CTRL To: KarimAllah Ahmed Cc: kvm list , LKML , "the arch/x86 maintainers" , Asit Mallick , Arjan Van De Ven , Dave Hansen , Andi Kleen , Andrea Arcangeli , Linus Torvalds , Tim Chen , Thomas Gleixner , Dan Williams , Jun Nakajima , Paolo Bonzini , David Woodhouse , Greg KH , Andy Lutomirski , Ashok Raj Content-Type: text/plain; charset="UTF-8" X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1591237580461918240?= X-GMAIL-MSGID: =?utf-8?q?1591312913961169749?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Thu, Feb 1, 2018 at 1:59 PM, KarimAllah Ahmed wrote: > [ Based on a patch from Ashok Raj ] > > 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. > > 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. > > 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. > > [dwmw2: Clean up CPUID bits, save/restore manually, handle reset] > > 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 Reviewed-by: Jim Mattson