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From: Maxim Levitsky <mlevitsk@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>, kvm@vger.kernel.org
Cc: Wanpeng Li <wanpengli@tencent.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	"open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
	<linux-kernel@vger.kernel.org>, Jim Mattson <jmattson@google.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Borislav Petkov <bp@alien8.de>,
	Joerg Roedel <joro@8bytes.org>, Ingo Molnar <mingo@redhat.com>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
	<x86@kernel.org>, Sean Christopherson <seanjc@google.com>,
	Cathy Avery <cavery@redhat.com>
Subject: Re: [PATCH 4/5] KVM: nSVM: force L1's GIF to 1 when setting the nested state
Date: Mon, 03 May 2021 17:24:20 +0300	[thread overview]
Message-ID: <21c774b2c1a4f5f90f615ac55b3eac22043854f2.camel@redhat.com> (raw)
In-Reply-To: <7d2fe4a1-9603-8bea-e7f1-fb3c24198941@redhat.com>

On Mon, 2021-05-03 at 16:00 +0200, Paolo Bonzini wrote:
> On 03/05/21 14:54, Maxim Levitsky wrote:
> > While after a reset the GIF value is already 1,
> > it doesn't have to have this value if the nested state
> > is loaded later.
> > 
> > Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> > ---
> >   arch/x86/kvm/svm/nested.c | 3 +++
> >   1 file changed, 3 insertions(+)
> > 
> > diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> > index 32400cba608d..12a12ae940fa 100644
> > --- a/arch/x86/kvm/svm/nested.c
> > +++ b/arch/x86/kvm/svm/nested.c
> > @@ -1314,6 +1314,9 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
> >   	else
> >   		svm->nested.vmcb02.ptr->save = svm->vmcb01.ptr->save;
> >   
> > +	/* Force L1's GIF to true */
> > +	svm_set_gif(svm, true);
> > +
> >   	svm->nested.nested_run_pending =
> >   		!!(kvm_state->flags & KVM_STATE_NESTED_RUN_PENDING);
> >   
> > 
> 
> Hmm, not sure about this one.  It is possible in principle to do CLGI in 
> L2 with the intercept disabled.

I need to think about this a bit more. 
In theory we have L0 GIF, the L1 GIF and the L2 GIF.
L0 GIF is always KVM's, so no problem.
L1 GIF can be toggled with L1 executing clgi/stgi, and it will be either stored in 
vmcb.int_ctl (vmcb01 or vmcb02) or in hflags depending if vGIF is enabled.
(the L1 owned bits are copied in nested_vmcb02_prepare_control)

For L2 we never advertise virtual gif and we don't let it set V_GIF_ENABLE_MASK
in int_ctl, so it either intercepts clgi/stgi and does its own businesses with it
or it doesn't intercept it in which case L2 indeed just modifies L1 GIF.


> 
> You need to use
> 
> svm_set_gif(svm, !!(kvm_state->flags & KVM_STATE_NESTED_GIF_SET));


Assuming that the above is correct, then indeed, this should be done,
so I'll send a patch for this.
Thanks a lot!!

Best regards,
	Maxim Levitsky



> 
> instead.
> 
> Paolo
> 



  reply	other threads:[~2021-05-03 14:24 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-03 12:54 [PATCH 0/5] KVM: nSVM: few fixes for the nested migration Maxim Levitsky
2021-05-03 12:54 ` [PATCH 1/5] KVM: nSVM: fix a typo in svm_leave_nested Maxim Levitsky
2021-05-03 12:54 ` [PATCH 2/5] KVM: nSVM: fix few bugs in the vmcb02 caching logic Maxim Levitsky
2021-05-03 12:54 ` [PATCH 3/5] KVM: nSVM: leave the guest mode prior to loading a nested state Maxim Levitsky
2021-05-03 12:54 ` [PATCH 4/5] KVM: nSVM: force L1's GIF to 1 when setting the " Maxim Levitsky
2021-05-03 14:00   ` Paolo Bonzini
2021-05-03 14:24     ` Maxim Levitsky [this message]
2021-05-03 12:54 ` [PATCH 5/5] KVM: nSVM: set a dummy exit reason in L1 vmcb when loading " Maxim Levitsky
2021-05-03 14:02   ` Paolo Bonzini
2021-05-03 14:26     ` Maxim Levitsky
2021-05-03 14:03 ` [PATCH 0/5] KVM: nSVM: few fixes for the nested migration Paolo Bonzini

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