Re: [PATCH 2/3] KVM: nVMX: KVM_SET_NESTED_STATE - Tear down old EVMCS state before setting new state

Aaron Lewis
2019-05-15T16:43:04Z

On Wed, May 8, 2019 at 2:18 PM Aaron Lewis <aaronlewis@google.com> wrote:
>
> From: Vitaly Kuznetsov <vkuznets@redhat.com>
> Date: Wed, May 8, 2019 at 12:55 PM
> To: Aaron Lewis
> Cc: Peter Shier, Paolo Bonzini, <rkrcmar@redhat.com>, Jim Mattson,
> Marc Orr, <kvm@vger.kernel.org>
>
> > Aaron Lewis <aaronlewis@google.com> writes:
> >
> > > From: Vitaly Kuznetsov <vkuznets@redhat.com>
> > > Date: Fri, May 3, 2019 at 3:25 AM
> > > To: Aaron Lewis
> > > Cc: Peter Shier, <pbonzini@redhat.com>, <rkrcmar@redhat.com>,
> > > <jmattson@google.com>, <marcorr@google.com>, <kvm@vger.kernel.org>
> > >
> > >> Aaron Lewis <aaronlewis@google.com> writes:
> > >>
> > >> > Move call to nested_enable_evmcs until after free_nested() is complete.
> > >> >
> > >> > Signed-off-by: Aaron Lewis <aaronlewis@google.com>
> > >> > Reviewed-by: Marc Orr <marcorr@google.com>
> > >> > Reviewed-by: Peter Shier <pshier@google.com>
> > >> > ---
> > >> > arch/x86/kvm/vmx/nested.c | 6 +++---
> > >> > 1 file changed, 3 insertions(+), 3 deletions(-)
> > >> >
> > >> > diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> > >> > index 081dea6e211a..3b39c60951ac 100644
> > >> > --- a/arch/x86/kvm/vmx/nested.c
> > >> > +++ b/arch/x86/kvm/vmx/nested.c
> > >> > @@ -5373,9 +5373,6 @@ static int vmx_set_nested_state(struct kvm_vcpu *vcpu,
> > >> > if (kvm_state->format != 0)
> > >> > return -EINVAL;
> > >> >
> > >> > - if (kvm_state->flags & KVM_STATE_NESTED_EVMCS)
> > >> > - nested_enable_evmcs(vcpu, NULL);
> > >> > -
> > >> > if (!nested_vmx_allowed(vcpu))
> > >> > return kvm_state->vmx.vmxon_pa == -1ull ? 0 : -EINVAL;
> > >> >
> > >> > @@ -5417,6 +5414,9 @@ static int vmx_set_nested_state(struct kvm_vcpu *vcpu,
> > >> > if (kvm_state->vmx.vmxon_pa == -1ull)
> > >> > return 0;
> > >> >
> > >> > + if (kvm_state->flags & KVM_STATE_NESTED_EVMCS)
> > >> > + nested_enable_evmcs(vcpu, NULL);
> > >> > +
> > >> > vmx->nested.vmxon_ptr = kvm_state->vmx.vmxon_pa;
> > >> > ret = enter_vmx_operation(vcpu);
> > >> > if (ret)
> > >>
> > >> nested_enable_evmcs() doesn't do much, actually, in case it was
> > >> previously enabled it doesn't do anything and in case it wasn't ordering
> > >> with free_nested() (where you're aiming at nested_release_evmcs() I
> > >> would guess) shouldn't matter. So could you please elaborate (better in
> > >> the commit message) why do we need this re-ordered? My guess is that
> > >> you'd like to perform checks for e.g. 'vmx.vmxon_pa == -1ull' before
> > >> we actually start doing any changes but let's clarify that.
> > >>
> > >> Thanks!
> > >>
> > >> --
> > >> Vitaly
> > >
> > > There are two reasons for doing this:
> > > 1. We don't want to set new state if we are going to leave nesting and
> > > exit the function (ie: vmx.vmxon_pa = -1), like you pointed out.
> > > 2. To be more future proof, we don't want to set new state before
> > > tearing down state. This could cause conflicts down the road.
> > >
> > > I can add this to the commit message if there are no objections to
> > > these points.
> >
> > Sounds good to me, please do. Thanks!
> >
> > --
> > Vitaly
>
> Here is the updated patch:
>
>
> Move call to nested_enable_evmcs until after free_nested() is
> complete. There are two reasons for doing this:
> 1. We don't want to set new state if we are going to leave nesting and
> exit the function (ie: vmx.vmxon_pa = -1).
> 2. To be more future proof, we don't want to set new state before
> tearing down state. This could cause conflicts down the road.
>
> Signed-off-by: Aaron Lewis <aaronlewis@google.com>
> Reviewed-by: Marc Orr <marcorr@google.com>
> Reviewed-by: Peter Shier <pshier@google.com>
> ---
> arch/x86/kvm/vmx/nested.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index fe5814df5149..6ecc301df874 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -5373,9 +5373,6 @@ static int vmx_set_nested_state(struct kvm_vcpu *vcpu,
> if (kvm_state->format != 0)
> return -EINVAL;
>
> - if (kvm_state->flags & KVM_STATE_NESTED_EVMCS)
> - nested_enable_evmcs(vcpu, NULL);
> -
> if (!nested_vmx_allowed(vcpu))
> return kvm_state->vmx.vmxon_pa == -1ull ? 0 : -EINVAL;
>
> @@ -5417,6 +5414,9 @@ static int vmx_set_nested_state(struct kvm_vcpu *vcpu,
> if (kvm_state->vmx.vmxon_pa == -1ull)
> return 0;
>
> + if (kvm_state->flags & KVM_STATE_NESTED_EVMCS)
> + nested_enable_evmcs(vcpu, NULL);
> +
> vmx->nested.vmxon_ptr = kvm_state->vmx.vmxon_pa;
> ret = enter_vmx_operation(vcpu);
> if (ret)

Hi Vitaly,

Does this update look good or are any other changes needed?

Thanks,
Aaron