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

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Message-ID: <20220412180452.ityo3o3eoxh3iul7@guptapa-desk>
Date:   Tue, 12 Apr 2022 11:04:52 -0700
From:   Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To:     Jon Kohler <jon@...anix.com>
Cc:     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 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.

   https://lore.kernel.org/lkml/de6b97a567e273adff1f5268998692bad548aa10.1623272033.git-series.pawan.kumar.gupta@linux.intel.com/

For the lack of real world use-cases at that time, this patch was dropped.

Thanks,
Pawan