From: Paolo Bonzini <pbonzini@redhat.com>
To: Filippo Sironi <sironi@amazon.de>,
rkrcmar@redhat.com, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] KVM: x86: Allow userspace to define what's the microcode version
Date: Mon, 27 Nov 2017 11:40:03 +0100 [thread overview]
Message-ID: <42809091-3330-c99b-0d11-218db66a3de9@redhat.com> (raw)
In-Reply-To: <1511714482-3273-2-git-send-email-sironi@amazon.de>
On 26/11/2017 17:41, Filippo Sironi wrote:
> ... that the guest should see.
> Guest operating systems may check the microcode version to decide whether
> to disable certain features that are known to be buggy up to certain
> microcode versions. Address the issue by making the microcode version
> that the guest should see settable.
What's the advantage of specifying the microcode version, rather than
relying on userspace to drop the CPUID bit for the buggy feature?
old guest(*) new guest
hide in CPUID good good
use ucode rev BAD good
(*) old guest = doesn't know that the feature is buggy until a given
ucode revision
Thanks,
Paolo
> The rationale for having userspace specifying the microcode version, rather
> than having the kernel picking it, is to ensure consistency for live-migrated
> instances; we don't want them to see a microcode version increase without a
> reset.
next prev parent reply other threads:[~2017-11-27 10:40 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-26 16:41 [PATCH 1/2] KVM: x86: Store the microcode version in struct kvm_arch Filippo Sironi
2017-11-26 16:41 ` [PATCH 2/2] KVM: x86: Allow userspace to define what's the microcode version Filippo Sironi
2017-11-27 1:02 ` Wanpeng Li
2017-12-09 7:21 ` Sironi, Filippo
2017-11-27 10:40 ` Paolo Bonzini [this message]
2017-12-09 7:33 ` Sironi, Filippo
2017-11-27 11:58 ` Paolo Bonzini
2017-11-27 22:09 ` Steve Rutherford
2017-12-09 7:51 ` Sironi, Filippo
2017-12-09 7:42 ` Sironi, Filippo
2017-12-11 16:03 ` Paolo Bonzini
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