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From: "Radim Krčmář" <rkrcmar@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
	David Woodhouse <dwmw@amazon.co.uk>,
	KarimAllah Ahmed <karahmed@amazon.de>
Subject: Re: [PATCH] KVM: VMX: expose the host's ARCH_CAPABILITIES MSR to userspace
Date: Thu, 1 Mar 2018 22:39:04 +0100	[thread overview]
Message-ID: <20180301213205.GB29001@flask> (raw)
In-Reply-To: <20180226221300.GK22024@char.us.oracle.com>

[Resent after removing g@char.us.oracle.com.]

2018-02-26 17:13-0500, Konrad Rzeszutek Wilk:
> On Sat, Feb 24, 2018 at 01:52:26AM +0100, Paolo Bonzini wrote:
> > Use the new MSR feature framework to expose the ARCH_CAPABILITIES MSR to
> > userspace.  This way, userspace can access the capabilities even if it
> > does not have the permissions to read MSRs.
> 
> ... That is good but could you expand a bit of why it would want this?
> 
> I am 99% sure it is due to the lovely spectre_v2 mitigation but
> could you include that in the commit message so that in say a year
> folks would know what this is?

Userspace can currently get the MSR by creating a VCPU and reading its
MSR_IA32_ARCH_CAPABILITIES, because it is set from the hardware MSR.

I thought that "permissions to read MSRs" talked about hardware MSRs, so
the purpose of this patch would be a better interface, but I don't see
how if we keep the auto-setting on VCPU creation.

Is this aimed towards userspaces that want nothing else from KVM than
the MSR value?

Thanks.

  parent reply	other threads:[~2018-03-01 21:39 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-02-24  0:52 [PATCH] KVM: VMX: expose the host's ARCH_CAPABILITIES MSR to userspace Paolo Bonzini
2018-02-26 22:13 ` Konrad Rzeszutek Wilk
2018-02-26 22:23   ` Konrad Rzeszutek Wilk
2018-03-01 21:39   ` Radim Krčmář [this message]
2018-03-02  9:36     ` Paolo Bonzini
2018-03-02 21:42       ` Radim Krčmář
2018-03-07 11:53         ` Paolo Bonzini
2018-03-07 14:56           ` Radim Krčmář
2018-03-07 15:10             ` Paolo Bonzini
2018-03-07 15:39               ` Radim Krčmář

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