linux-kernel - Re: [PATCH v2] kvm: nVMX: Set nested_run_pending in vmx_set_nested

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Date:   Wed, 8 May 2019 10:53:12 -0700
From:   Aaron Lewis <aaronlewis@...gle.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, Peter Shier <pshier@...gle.com>
Subject: Re: [PATCH v2] kvm: nVMX: Set nested_run_pending in
 vmx_set_nested_state after checks complete

From: Sean Christopherson <sean.j.christopherson@...el.com>
Date: Wed, May 8, 2019 at 7:20 AM
To: Paolo Bonzini
Cc: <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>, Peter
Shier, Aaron Lewis

> On Wed, May 08, 2019 at 02:16:39PM +0200, Paolo Bonzini wrote:
> > From: Aaron Lewis <aaronlewis@...gle.com>
>
> If this is actually attributed to Aaron it needs his SOB.
>
> > nested_run_pending=1 implies we have successfully entered guest mode.
> > Move setting from external state in vmx_set_nested_state() until after
> > all other checks are complete.
>
> It'd be helpful to at least mention the flag is consumed by
> nested_vmx_enter_non_root_mode().
>
> > Based on a patch by Aaron Lewis.
> >
> > Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> > ---
>
> For the code itself:
>
> Reviewed-by: Sean Christopherson <sean.j.christopherson@...el.com>
>
> >  arch/x86/kvm/vmx/nested.c | 10 ++++++----
> >  1 file changed, 6 insertions(+), 4 deletions(-)
> >
> > diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> > index cec77f30f61c..e58caff92694 100644
> > --- a/arch/x86/kvm/vmx/nested.c
> > +++ b/arch/x86/kvm/vmx/nested.c
> > @@ -5420,9 +5420,6 @@ static int vmx_set_nested_state(struct kvm_vcpu *vcpu,
> >       if (!(kvm_state->flags & KVM_STATE_NESTED_GUEST_MODE))
> >               return 0;
> >
> > -     vmx->nested.nested_run_pending =
> > -             !!(kvm_state->flags & KVM_STATE_NESTED_RUN_PENDING);
> > -
> >       if (nested_cpu_has_shadow_vmcs(vmcs12) &&
> >           vmcs12->vmcs_link_pointer != -1ull) {
> >               struct vmcs12 *shadow_vmcs12 = get_shadow_vmcs12(vcpu);
> > @@ -5446,9 +5443,14 @@ static int vmx_set_nested_state(struct kvm_vcpu *vcpu,
> >               return -EINVAL;
> >
> >       vmx->nested.dirty_vmcs12 = true;
> > +     vmx->nested.nested_run_pending =
> > +             !!(kvm_state->flags & KVM_STATE_NESTED_RUN_PENDING);
> > +
> >       ret = nested_vmx_enter_non_root_mode(vcpu, false);
> > -     if (ret)
> > +     if (ret) {
> > +             vmx->nested.nested_run_pending = 0;
> >               return -EINVAL;
> > +     }
> >
> >       return 0;
> >  }
> > --
> > 1.8.3.1
> >

nested_run_pending is also checked in
nested_vmx_check_vmentry_postreqs
(https://elixir.bootlin.com/linux/v5.1/source/arch/x86/kvm/vmx/nested.c#L2709)
so I think the setting needs to be moved to just prior to that call
with Paolo's rollback along with another for if the prereqs and
postreqs fail.  I put a patch together below:

------------------------------------

nested_run_pending=1 implies we have successfully entered guest mode.
Move setting from external state in vmx_set_nested_state() until after
all other checks are complete.

Signed-off-by: Aaron Lewis <aaronlewis@...gle.com>
Reviewed-by: Peter Shier <pshier@...gle.com>
---
 arch/x86/kvm/vmx/nested.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 6401eb7ef19c..cf1f810223d2 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -5460,9 +5460,6 @@ static int vmx_set_nested_state(struct kvm_vcpu *vcpu,
  if (!(kvm_state->flags & KVM_STATE_NESTED_GUEST_MODE))
  return 0;

- vmx->nested.nested_run_pending =
- !!(kvm_state->flags & KVM_STATE_NESTED_RUN_PENDING);
-
  if (nested_cpu_has_shadow_vmcs(vmcs12) &&
      vmcs12->vmcs_link_pointer != -1ull) {
  struct vmcs12 *shadow_vmcs12 = get_shadow_vmcs12(vcpu);
@@ -5480,14 +5477,21 @@ static int vmx_set_nested_state(struct kvm_vcpu *vcpu,
  return -EINVAL;
  }

+ vmx->nested.nested_run_pending =
+ !!(kvm_state->flags & KVM_STATE_NESTED_RUN_PENDING);
+
  if (nested_vmx_check_vmentry_prereqs(vcpu, vmcs12) ||
-     nested_vmx_check_vmentry_postreqs(vcpu, vmcs12, &exit_qual))
+     nested_vmx_check_vmentry_postreqs(vcpu, vmcs12, &exit_qual)) {
+     vmx->nested.nested_run_pending = 0;
  return -EINVAL;
+ }

  vmx->nested.dirty_vmcs12 = true;
  ret = nested_vmx_enter_non_root_mode(vcpu, false);
- if (ret)
+ if (ret) {
+ vmx->nested.nested_run_pending = 0;
  return -EINVAL;
+ }

  return 0;
 }