linux-kernel - Re: [PATCH RFC 1/3] x86/kvm/vmx: read MSR_FS

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Date:   Mon, 05 Mar 2018 10:56:11 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH RFC 1/3] x86/kvm/vmx: read MSR_FS_BASE from current->thread

Andy Lutomirski <luto@...nel.org> writes:

> On Fri, Mar 2, 2018 at 10:55 AM, Vitaly Kuznetsov <vkuznets@...hat.com> wrote:
>> vmx_save_host_state() is only called from kvm_arch_vcpu_ioctl_run() so
>> the context is pretty well defined
>>
>
> True.
>
>> and MSR_FS_BASE should always be
>> equal to current->thread.fsbase.
>
> Not true.  current->thread.fsbase is almost entirely undefined in this
> context.  What you *could* do is export save_fsgs() and call it first.
> When FSGSBASE support lands (which will happen eventually!), the code
> in your patch will be completely wrong.
>
> Admittedly, your patch isn't 100% bogus, but the reason is subtle and
> you need lots of comments there *and* in save_fsgs().

Thank you Andy,

I'll take a look.

-- 
  Vitaly