linux-kernel - Re: [PATCH 2/2] kvm: nVMX: Introduce KVM_CAP

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Date:   Mon, 16 Apr 2018 17:15:37 +0000
From:   "Raslan, KarimAllah" <karahmed@...zon.de>
To:     "jmattson@...gle.com" <jmattson@...gle.com>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>
Subject: Re: [PATCH 2/2] kvm: nVMX: Introduce KVM_CAP_STATE

On Mon, 2018-04-16 at 09:22 -0700, Jim Mattson wrote:
> On Thu, Apr 12, 2018 at 8:12 AM, KarimAllah Ahmed <karahmed@...zon.de> wrote:
> 
> > 
> > v2 -> v3:
> > - Remove the forced VMExit from L2 after reading the kvm_state. The actual
> >   problem is solved.
> > - Rebase again!
> > - Set nested_run_pending during restore (not sure if it makes sense yet or
> >   not).
> 
> This doesn't actually make sense. Nested_run_pending should only be
> set between L1 doing a VMLAUNCH/VMRESUME and the first instruction
> executing in L2. That is extremely unlikely at a restore point.

Yeah, I am afraid I put very little thought into it as I was focused
on the TSC issue :)

Will handle it properly in next version.

> 
> To deal with nested_run_pending and nested save/restore,
> nested_run_pending should be set to 1 before calling
> enter_vmx_non_root_mode, as it was prior to commit 7af40ad37b3f. That
> means that it has to be cleared when emulating VM-entry to the halted
> state (prior to calling kvm_vcpu_halt). And all of the from_vmentry
> arguments that Paolo added when rebasing commit cf8b84f48a59 should be
> removed, so that nested_run_pending is propagated correctly duting a
> restore.
> 
> It should be possible to eliminate this strange little wart, but I
> haven't looked deeply into it.
> 
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