From: Dave Hansen <dave.hansen@intel.com>
To: Jim Mattson <jmattson@google.com>
Cc: Sean Christopherson <seanjc@google.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Arjan van de Ven <arjan@linux.intel.com>
Subject: Re: Finish removing MPX from arch/x86?
Date: Tue, 4 Oct 2022 14:07:45 -0700 [thread overview]
Message-ID: <c7a0b0f1-5a74-7f8c-b707-bce8086bc4c7@intel.com> (raw)
In-Reply-To: <CALMp9eRTp9Jemy91o0S9Fz4JYFdQ5rM36g4uWhp5LsncCQHRwA@mail.gmail.com>
On 10/4/22 11:21, Jim Mattson wrote:
> On Tue, Oct 4, 2022 at 10:45 AM Dave Hansen <dave.hansen@intel.com> wrote:
>>
>> We zapped the userspace MPX ABIs and most of its supporting code in here:
>>
>> 45fc24e89b7c ("x86/mpx: remove MPX from arch/x86")
>>
>> But, the XSAVE enabling and KVM code were left in place. This let folks
>> at least keep running guests with MPX.
>>
>> It's been a couple of years and I don't think I've had a single person
>> opine about the loss of MPX. Intel also followed through and there's no
>> MPX to be found on newer CPUs like my "Tiger Lake" 11th Gen Intel(R)
>> Core(TM) i7-1165G7.
>>
>> Is it time to zap MPX from arch/x86/kvm/?
>
> Until Google Cloud retires all of our MPX-capable hardware, we will
> require MPX support in KVM.
>
> Removing that support would leave VMs with MPX enabled in XCR0 with
> nowhere to go.
Is this because you migrate guest VMs between hosts? A _potential_ VM
migration target host is ineligible if it has a subset of the features
of the source host?
Would it be _possible_ to leave existing VMs alone, but to stop
enumerating MPX to newly-created VMs? I don't know how long-lived your
VMs are, but I'm hoping that the ones that know about MPX will all die
naturally of old age at some point.
next prev parent reply other threads:[~2022-10-04 21:07 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-04 17:34 Dave Hansen
2022-10-04 18:21 ` Jim Mattson
2022-10-04 21:07 ` Dave Hansen [this message]
2022-10-04 21:42 ` Jim Mattson
2022-10-05 12:04 ` Paolo Bonzini
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