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

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Message-ID: <CALMp9eSS4nL1-1i1Df=vyPFT1FZVprPB0Yx-JX0auknNc09Gtg@mail.gmail.com>
Date:   Mon, 16 Apr 2018 09:22:47 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     KarimAllah Ahmed <karahmed@...zon.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: [PATCH 2/2] kvm: nVMX: Introduce KVM_CAP_STATE

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.

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.