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From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: "kvm list" <kvm@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>, "X86 ML" <x86@kernel.org>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Radim Krčmář" <rkrcmar@redhat.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Ingo Molnar" <mingo@redhat.com>,
	"H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH RFC 1/3] x86/kvm/vmx: read MSR_FS_BASE from current->thread
Date: Mon, 05 Mar 2018 10:56:11 +0100	[thread overview]
Message-ID: <874llu26dg.fsf@vitty.brq.redhat.com> (raw)
In-Reply-To: <CALCETrX0CB_+QvDH3B8fYdH+ekRRX-i=jZU7zQ8qYbGzDrM-uQ@mail.gmail.com> (Andy Lutomirski's message of "Fri, 2 Mar 2018 20:18:18 +0000")

Andy Lutomirski <luto@kernel.org> writes:

> On Fri, Mar 2, 2018 at 10:55 AM, Vitaly Kuznetsov <vkuznets@redhat.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

  reply	other threads:[~2018-03-05  9:56 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-03-02 10:55 [PATCH RFC 0/3] x86/kvm: avoid expensive rdmsrs for FS/GS base MSRs Vitaly Kuznetsov
2018-03-02 10:55 ` [PATCH RFC 1/3] x86/kvm/vmx: read MSR_FS_BASE from current->thread Vitaly Kuznetsov
2018-03-02 20:18   ` Andy Lutomirski
2018-03-05  9:56     ` Vitaly Kuznetsov [this message]
2018-03-07 13:15     ` Vitaly Kuznetsov
2018-03-02 10:55 ` [PATCH RFC 2/3] x86/kvm/vmx: read MSR_KERNEL_GS_BASE " Vitaly Kuznetsov
2018-03-02 10:55 ` [PATCH RFC 3/3] x86/kvm/vmx: avoid expensive rdmsr for MSR_GS_BASE Vitaly Kuznetsov
2018-03-02 20:20   ` Andy Lutomirski
2018-03-05 10:04     ` Vitaly Kuznetsov
2018-03-06 10:16 ` [PATCH RFC 0/3] x86/kvm: avoid expensive rdmsrs for FS/GS base MSRs Paolo Bonzini

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