LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Jim Mattson <jmattson@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Raslan, KarimAllah" <karahmed@amazon.de>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"x86@kernel.org" <x86@kernel.org>,
	"hpa@zytor.com" <hpa@zytor.com>,
	"mingo@redhat.com" <mingo@redhat.com>,
	"rkrcmar@redhat.com" <rkrcmar@redhat.com>
Subject: Re: [PATCH 2/2] kvm: nVMX: Introduce KVM_CAP_STATE
Date: Fri, 27 Apr 2018 08:19:13 -0700	[thread overview]
Message-ID: <CALMp9eSG-nAuJEyavJoBp7QS1_VuYpuNSjKNUoK6MMEeywypeQ@mail.gmail.com> (raw)
In-Reply-To: <f8875546-da53-fc36-d3da-5b5ff089ccc0@redhat.com>

On Fri, Apr 27, 2018 at 3:03 AM, Paolo Bonzini <pbonzini@redhat.com> wrote:
> On 27/04/2018 00:28, Jim Mattson wrote:
>> The other thing that comes to mind is that there are some new fields
>> in the VMCS12 since I first implemented this. One potentially
>> troublesome field is the VMX preemption timer. If the current timer
>> value is not saved on VM-exit, then it won't be stashed in the shadow
>> VMCS12 by sync_vmcs12. Post-migration, the timer will be reset to its
>> original value.
>>
>> Do we care? Is this any different from what happens on real hardware
>> when there's an SMI? According to the SDM, this appears to be exacty
>> what happens when the dual-monitor treatment of SMIs and SMM is
>> active, but it's not clear what happens with the default treatment of
>> SMIs and SMM.
>
> I think it should be the same, because the preemption timer countdown is
> not part of the VMX-critical state.
>
> Paolo

Section 25.5.1 of the SDM says:

If the default treatment of SMIs and SMM (see Section 34.14) is
active, the VMX-preemption timer counts across an SMI to VMX non-root
operation, subsequent execution in SMM, and the return from SMM via
the RSM instruction. However, the timer can cause a VM exit only from
VMX non-root operation. If the timer expires during SMI, in SMM, or
during RSM, a timer-induced VM exit occurs immediately after RSM with
its normal priority unless it is blocked based on activity state
(Section 25.2).

So, there's no loophole here that allows us to reset the VMX
preemption timer when restoring nested state.

As a follow-on change, we should probably fix this.

  reply	other threads:[~2018-04-27 15:19 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-12 15:12 [PATCH 1/2] X86/KVM: Properly restore 'tsc_offset' when running an L2 guest KarimAllah Ahmed
2018-04-12 15:12 ` [PATCH 2/2] kvm: nVMX: Introduce KVM_CAP_STATE KarimAllah Ahmed
2018-04-12 16:39   ` Paolo Bonzini
2018-04-14 15:56   ` Raslan, KarimAllah
2018-04-14 22:31     ` Raslan, KarimAllah
2018-04-16 16:22   ` Jim Mattson
2018-04-16 17:15     ` Raslan, KarimAllah
2018-04-26 22:28       ` Jim Mattson
2018-04-27 10:03         ` Paolo Bonzini
2018-04-27 15:19           ` Jim Mattson [this message]
2018-04-28  0:42             ` Paolo Bonzini
2018-04-12 16:35 ` [PATCH 1/2] X86/KVM: Properly restore 'tsc_offset' when running an L2 guest Paolo Bonzini
2018-04-12 17:04   ` Raslan, KarimAllah
2018-04-12 17:21     ` Raslan, KarimAllah
2018-04-12 20:21       ` Paolo Bonzini
2018-04-12 20:24         ` Raslan, KarimAllah

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=CALMp9eSG-nAuJEyavJoBp7QS1_VuYpuNSjKNUoK6MMEeywypeQ@mail.gmail.com \
    --to=jmattson@google.com \
    --cc=hpa@zytor.com \
    --cc=karahmed@amazon.de \
    --cc=kvm@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@redhat.com \
    --cc=pbonzini@redhat.com \
    --cc=rkrcmar@redhat.com \
    --cc=tglx@linutronix.de \
    --cc=x86@kernel.org \
    --subject='Re: [PATCH 2/2] kvm: nVMX: Introduce KVM_CAP_STATE' \
    /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

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).