linux-kernel - Re: [PATCH v19 118/130] KVM: TDX: Add methods to ignore accesses to CPU state

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Message-ID: <20240419180924.GF3596705@ls.amr.corp.intel.com>
Date: Fri, 19 Apr 2024 11:09:24 -0700
From: Isaku Yamahata <isaku.yamahata@...el.com>
To: Binbin Wu <binbin.wu@...ux.intel.com>
Cc: isaku.yamahata@...el.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, isaku.yamahata@...il.com,
	Paolo Bonzini <pbonzini@...hat.com>, erdemaktas@...gle.com,
	Sean Christopherson <seanjc@...gle.com>,
	Sagi Shahar <sagis@...gle.com>, Kai Huang <kai.huang@...el.com>,
	chen.bo@...el.com, hang.yuan@...el.com, tina.zhang@...el.com,
	isaku.yamahata@...ux.intel.com
Subject: Re: [PATCH v19 118/130] KVM: TDX: Add methods to ignore accesses to
 CPU state

On Fri, Apr 19, 2024 at 06:04:10PM +0800,
Binbin Wu <binbin.wu@...ux.intel.com> wrote:

> 
> 
> On 2/26/2024 4:27 PM, isaku.yamahata@...el.com wrote:
> > From: Isaku Yamahata <isaku.yamahata@...el.com>
> > 
> > TDX protects TDX guest state from VMM.  Implement access methods for TDX
> > guest state to ignore them or return zero.  Because those methods can be
> > called by kvm ioctls to set/get cpu registers, they don't have KVM_BUG_ON
> > except one method.
> > 
> > Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> > ---
> >   arch/x86/kvm/vmx/main.c    | 289 +++++++++++++++++++++++++++++++++----
> >   arch/x86/kvm/vmx/tdx.c     |  48 +++++-
> >   arch/x86/kvm/vmx/x86_ops.h |  13 ++
> >   3 files changed, 321 insertions(+), 29 deletions(-)
> > 
> > diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
> > index 84d2dc818cf7..9fb3f28d8259 100644
> > --- a/arch/x86/kvm/vmx/main.c
> > +++ b/arch/x86/kvm/vmx/main.c
> > @@ -375,6 +375,200 @@ static void vt_vcpu_deliver_init(struct kvm_vcpu *vcpu)
> >   	kvm_vcpu_deliver_init(vcpu);
> >   }
> > +static void vt_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
> > +{
> > +	if (is_td_vcpu(vcpu))
> > +		return;
> > +
> > +	vmx_vcpu_after_set_cpuid(vcpu);
> > +}
> > +
> > +static void vt_update_exception_bitmap(struct kvm_vcpu *vcpu)
> > +{
> > +	if (is_td_vcpu(vcpu))
> > +		return;
> > +
> > +	vmx_update_exception_bitmap(vcpu);
> > +}
> > +
> > +static u64 vt_get_segment_base(struct kvm_vcpu *vcpu, int seg)
> > +{
> > +	if (is_td_vcpu(vcpu))
> > +		return tdx_get_segment_base(vcpu, seg);
> Could just return 0?
> Not need to add a function, since it's only called here and it's more
> straight forward to read the code without jump to the definition of these
> functions.
> 
> Similarly, we can use open code for tdx_get_cpl(), tdx_get_rflags() and
> tdx_get_segment(), which return 0 or memset with 0.

Yes, we should drop them. They came from the TDX guest debug.  But right now
we drop the support and we have guard with vcpu->arch.guest_state_protected.

guest debug is a future topic now.
-- 
Isaku Yamahata <isaku.yamahata@...el.com>