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From: "Raj, Ashok" <ashok.raj@intel.com>
To: KarimAllah Ahmed <karahmed@amazon.de>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	x86@kernel.org, Asit Mallick <asit.k.mallick@intel.com>,
	Arjan Van De Ven <arjan.van.de.ven@intel.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Andi Kleen <ak@linux.intel.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Tim Chen <tim.c.chen@linux.intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Dan Williams <dan.j.williams@intel.com>,
	Jun Nakajima <jun.nakajima@intel.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	David Woodhouse <dwmw@amazon.co.uk>,
	Greg KH <gregkh@linuxfoundation.org>,
	Andy Lutomirski <luto@kernel.org>,
	Ashok Raj <ashok.raj@intel.com>
Subject: Re: [PATCH v5 4/5] KVM: VMX: Allow direct access to MSR_IA32_SPEC_CTRL
Date: Wed, 31 Jan 2018 14:56:42 -0800	[thread overview]
Message-ID: <20180131225642.GA39829@otc-nc-03> (raw)
In-Reply-To: <1517427467-28567-5-git-send-email-karahmed@amazon.de>

Hi Karim

On Wed, Jan 31, 2018 at 08:37:46PM +0100, KarimAllah Ahmed wrote:
> [ Based on a patch from Ashok Raj <ashok.raj@intel.com> ]
> 
> 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.

With these changes SPEC_CTRL is properly exposed to the guest when using
latest Qemu.

> 
> To avoid the overhead of atomically saving and restoring the
> MSR_IA32_SPEC_CTRL for guests that do not actually use the MSR, only
> add_atomic_switch_msr 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]
> 

  parent reply	other threads:[~2018-01-31 22:56 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-31 19:37 [PATCH v5 0/5] KVM: Expose speculation control feature to guests KarimAllah Ahmed
2018-01-31 19:37 ` [PATCH v5 1/5] KVM: x86: Update the reverse_cpuid list to include CPUID_7_EDX KarimAllah Ahmed
2018-01-31 20:22   ` Konrad Rzeszutek Wilk
2018-01-31 19:37 ` [PATCH v5 2/5] KVM: x86: Add IBPB support KarimAllah Ahmed
2018-01-31 19:45   ` Jim Mattson
2018-01-31 19:53     ` David Woodhouse
2018-01-31 19:55       ` Jim Mattson
2018-02-01  0:27         ` KarimAllah Ahmed
2018-01-31 20:28   ` Konrad Rzeszutek Wilk
2018-01-31 20:36     ` KarimAllah Ahmed
2018-02-01  4:54   ` Tom Lendacky
2018-02-01 17:00   ` Raj, Ashok
2018-01-31 19:37 ` [PATCH v5 3/5] KVM: VMX: Emulate MSR_IA32_ARCH_CAPABILITIES KarimAllah Ahmed
2018-01-31 19:37 ` [PATCH v5 4/5] KVM: VMX: Allow direct access to MSR_IA32_SPEC_CTRL KarimAllah Ahmed
2018-01-31 19:53   ` Jim Mattson
2018-01-31 20:00     ` David Woodhouse
2018-01-31 20:01     ` KarimAllah Ahmed
2018-01-31 20:18       ` Jim Mattson
2018-01-31 20:21         ` David Woodhouse
2018-01-31 21:18           ` Jim Mattson
2018-01-31 22:05             ` David Woodhouse
2018-01-31 20:34         ` Paolo Bonzini
2018-01-31 20:54           ` Jim Mattson
2018-01-31 21:00             ` Paolo Bonzini
2018-01-31 21:05               ` Jim Mattson
2018-01-31 21:17                 ` Woodhouse, David
2018-01-31 21:42                 ` Paolo Bonzini
2018-01-31 21:53                   ` Jim Mattson
2018-01-31 21:59                     ` Paolo Bonzini
2018-01-31 21:59                     ` David Woodhouse
2018-01-31 22:06                       ` Jim Mattson
2018-01-31 22:10                         ` David Woodhouse
2018-01-31 22:21                           ` Linus Torvalds
2018-01-31 22:53                         ` Andy Lutomirski
2018-02-01 14:09                       ` Paolo Bonzini
2018-01-31 22:52         ` KarimAllah Ahmed
2018-02-01  0:24           ` KarimAllah Ahmed
2018-02-01  4:26             ` Konrad Rzeszutek Wilk
2018-02-01 13:25               ` David Woodhouse
2018-02-01 17:37                 ` KarimAllah Ahmed
2018-02-01 17:46                   ` KarimAllah Ahmed
2018-02-01 14:19               ` Konrad Rzeszutek Wilk
2018-02-01 14:28                 ` KarimAllah Ahmed
2018-01-31 22:56   ` Raj, Ashok [this message]
2018-01-31 19:37 ` [PATCH v5 5/5] KVM: SVM: " KarimAllah Ahmed

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