linux-kernel - Re: [PATCH] x86/tsx: fix KVM guest live migration for tsx=on

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Date:   Tue, 12 Apr 2022 18:12:00 +0000
From:   Jon Kohler <jon@...anix.com>
To:     Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
CC:     Jon Kohler <jon@...anix.com>, Dave Hansen <dave.hansen@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, Tony Luck <tony.luck@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Borislav Petkov <bp@...e.de>,
        Neelima Krishnan <neelima.krishnan@...el.com>,
        "kvm @ vger . kernel . org" <kvm@...r.kernel.org>
Subject: Re: [PATCH] x86/tsx: fix KVM guest live migration for tsx=on



> On Apr 12, 2022, at 2:04 PM, Pawan Gupta <pawan.kumar.gupta@...ux.intel.com> wrote:
> 
> On Tue, Apr 12, 2022 at 04:08:32PM +0000, Jon Kohler wrote:
>> 
>> 
>>> On Apr 12, 2022, at 11:54 AM, Dave Hansen <dave.hansen@...el.com> wrote:
>>> 
>>> On 4/12/22 06:36, Jon Kohler wrote:
>>>> So my theory here is to extend the logical effort of the microcode driven
>>>> automatic disablement as well as the tsx=auto automatic disablement and
>>>> have tsx=on force abort all transactions on X86_BUG_TAA SKUs, but leave
>>>> the CPU features enumerated to maintain live migration.
>>>> 
>>>> This would still leave TSX totally good on Ice Lake / non-buggy systems.
>>>> 
>>>> If it would help, I'm working up an RFC patch, and we could discuss there?
>>> 
>>> Sure.  But, it sounds like you really want a new tdx=something rather
>>> than to muck with tsx=on behavior.  Surely someone else will come along
>>> and complain that we broke their TDX setup if we change its behavior.
>> 
>> Good point, there will always be a squeaky wheel. I’ll work that into the RFC,
>> I’ll do something like tsx=compat and see how it shapes up.
> 
> FYI, the original series had tsx=fake, that would have taken care of
> this breakage.

Fake sounds way better than compat, which is what I had :) 

My RFC code looks similar to your patch, I’ll combine the
approaches and send it out shortly, almost done

> 
>  https://urldefense.proofpoint.com/v2/url?u=https-3A__lore.kernel.org_lkml_de6b97a567e273adff1f5268998692bad548aa10.1623272033.git-2Dseries.pawan.kumar.gupta-40linux.intel.com_&d=DwIDaQ&c=s883GpUCOChKOHiocYtGcg&r=NGPRGGo37mQiSXgHKm5rCQ&m=AgPWHzCORdn5x5rYXE0QeJ2yf158HOjDA5Bn8udzp-m6i9V9s7S_jtSiLog-dk93&s=kR74kfovpa0zOK0tZ2Ss9xbg2aRLI5oocB_cp_6DLkg&e= 
> For the lack of real world use-cases at that time, this patch was dropped.
> 
> Thanks,
> Pawan