linux-kernel - Re: [PATCH 7/9] KVM/VMX: Emulate MSR_IA32_ARCH

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Message-ID: <a4693ca3-face-e1f5-b619-74fc59870ce9@redhat.com>
Date:   Mon, 19 Feb 2018 14:10:11 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Jim Mattson <jmattson@...gle.com>
Cc:     David Woodhouse <dwmw@...zon.co.uk>,
        Radim Krčmář <rkrcmar@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>,
        KarimAllah Ahmed <karahmed@...zon.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH 7/9] KVM/VMX: Emulate MSR_IA32_ARCH_CAPABILITIES

On 16/02/2018 17:29, Jim Mattson wrote:
> On Fri, Feb 16, 2018 at 6:18 AM, Paolo Bonzini <pbonzini@...hat.com> wrote:
> 
>> Uhm, taking contents from the hardware is wrong (guess why---live
>> migration).  I'll send a revert of those two lines.
> 
> Hardware seems like a reasonable place to get the default value (cf.
> the VMX capability MSRs).

There are some differences:

- a zero value for ARCH_CAPABILITIES should be safe, while a zero value
for VMX capabilities doesn't really make sense.  On the contrary, a
nonzero value for ARCH_CAPABILITIES is not safe across live migration.

- VMX doesn't support live migration; before adding that support we will
probably have Tom's patches to retrieve MSR capabilities.

Thanks,

Paolo

> Should these two lines just be moved to
> vmx_create_cpu?
>