From: Sean Christopherson <seanjc@google.com>
To: Jim Mattson <jmattson@google.com>
Cc: Oliver Upton <oupton@google.com>,
kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Joerg Roedel <joro@8bytes.org>
Subject: Re: [PATCH 0/4] KVM: nVMX: Fixes for VMX capability MSR invariance
Date: Thu, 3 Feb 2022 00:33:29 +0000 [thread overview]
Message-ID: <Yfsi2dSZ6Ga3SnIh@google.com> (raw)
In-Reply-To: <CALMp9eRotJRKXwPp=kVdfDjGBkqMJ+6wM+N=-7WnN7yr-azvxQ@mail.gmail.com>
On Wed, Feb 02, 2022, Jim Mattson wrote:
> On Wed, Feb 2, 2022 at 3:04 PM Oliver Upton <oupton@google.com> wrote:
> >
> > Ultimately, it is the responsibility of userspace to configure an
> > appropriate MSR value for the CPUID it provides its guest. However,
> > there are a few bits in VMX capability MSRs where KVM intervenes. The
> > "load IA32_PERF_GLOBAL_CTRL", "load IA32_BNDCFGS", and "clear
> > IA32_BNDCFGS" bits in the VMX VM-{Entry,Exit} control capability MSRs
> > are updated every time userspace sets the guest's CPUID. In so doing,
> > there is an imposed ordering between ioctls, that userspace must set MSR
> > values *after* setting the guest's CPUID.
>
> Do you mean *before*?
No, after, otherwise the CPUID updates will override the MSR updates.
MSR_IA32_FEAT_CTL has this same issue. But that mess also highlights an issue
with this series: if userspace relies on KVM to do the updates, it will break the
existing ABI, e.g. I'm pretty sure older versions of QEMU rely on KVM to adjust
the MSRs.
I agree that KVM should keep its nose out of this stuff, especially since most
VMX controls are technically not architecturally tied to CPUID. But we probably
need an opt-in from userspace to stop mucking with the MSRs.
next prev parent reply other threads:[~2022-02-03 0:33 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-02 23:04 [PATCH 0/4] KVM: nVMX: Fixes for VMX capability MSR invariance Oliver Upton
2022-02-02 23:04 ` [PATCH 1/4] KVM: nVMX: Don't change VM-{Entry,Exit} ctrl MSRs on PMU CPUID update Oliver Upton
2022-02-02 23:04 ` [PATCH 2/4] KVM: nVMX: Don't change VM-{Entry,Exit} ctrl MSRs on MPX " Oliver Upton
2022-02-02 23:04 ` [PATCH 3/4] selftests: KVM: Add test for "load IA32_PERF_GLOBAL_CTRL" invariance Oliver Upton
2022-02-02 23:04 ` [PATCH 4/4] selftests: KVM: Add test case for "{load/clear} IA32_BNDCFGS" invariance Oliver Upton
2022-02-03 0:04 ` [PATCH 0/4] KVM: nVMX: Fixes for VMX capability MSR invariance Jim Mattson
2022-02-03 0:33 ` Sean Christopherson [this message]
2022-02-03 0:38 ` Jim Mattson
2022-02-03 0:44 ` Oliver Upton
2022-02-03 0:48 ` Sean Christopherson
2022-02-03 0:42 ` Oliver Upton
2022-02-03 0:55 ` Sean Christopherson
2022-02-03 1:05 ` Oliver Upton
2022-02-03 1:08 ` Jim Mattson
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=Yfsi2dSZ6Ga3SnIh@google.com \
--to=seanjc@google.com \
--cc=jmattson@google.com \
--cc=joro@8bytes.org \
--cc=kvm@vger.kernel.org \
--cc=oupton@google.com \
--cc=pbonzini@redhat.com \
--cc=vkuznets@redhat.com \
--cc=wanpengli@tencent.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.