Re: [PATCH] vmx/nested: Set the SGX feature flag only when hardware supported.

[Huang, Kai]

On Tue, 2026-03-31 at 09:30 -0700, Sean Christopherson wrote:
> On Tue, Mar 24, 2026, Kai Huang wrote:
> > On Tue, 2026-03-24 at 11:27 +0800, 18341265598@xxxxxxx wrote:
> > > From: "zhaoge.zhang" <zhangzg12@xxxxxxxxxxxxxxx>
> > > 
> > > If the hardware does not support the SGX feature and we set the
> > > corresponding flag, when the L1 hypervisor enables the corresponding
> > > feature in VMCS12, the VM entry will fail.
> > > 
> > > Reported-by: wei xiaoqiong <weixq1@xxxxxxxxxxxxxxx>
> > > Signed-off-by: zhaoge.zhang <zhangzg12@xxxxxxxxxxxxxxx>
> > > Reviewed-by: Huaitong Han <hanht2@xxxxxxxxxxxxxxx>
> > > ---
> > >  arch/x86/kvm/vmx/nested.c |  2 +-
> > >  arch/x86/kvm/vmx/vmx.c    | 11 -----------
> > >  arch/x86/kvm/vmx/vmx.h    | 11 +++++++++++
> > >  3 files changed, 12 insertions(+), 12 deletions(-)
> > > 
> > > diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> > > index 937aeb4..396ac07 100644
> > > --- a/arch/x86/kvm/vmx/nested.c
> > > +++ b/arch/x86/kvm/vmx/nested.c
> > > @@ -7278,7 +7278,7 @@ static void nested_vmx_setup_secondary_ctls(u32 ept_caps,
> > >  		msrs->secondary_ctls_high |=
> > >  			SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES;
> > >  
> > > -	if (enable_sgx)
> > > +	if (enable_sgx && cpu_has_sgx())
> > >  		msrs->secondary_ctls_high |= SECONDARY_EXEC_ENCLS_EXITING;
> > >  }
> > 
> > Are you seeing the case where enable_sgx is true but cpu_has_sgx() reports
> > false?
> > 
> > It's quite strange because during KVM load, if cpu_has_sgx() is false,
> > enable_sgx is guaranteed to be false.
> > 
> > The only case that I can think of is after KVM loads somehow machine check
> > happens, which "soft disables" SGX (CPUID reports SGX1 as 0).
> > 
> > Is this the case you are meeting?
> 
> It's a moot point (unless I'm getting -ENOCOFFEE, which is very possible at the
> moment), because "enable_sgx" is cleared if ENCLS-exiting isn't supported.
> 
> 	if (!cpu_has_vmx_encls_vmexit())
> 		enable_sgx = false;
> 
> Where cpu_has_vmx_encls_vmexit() is peeking at vmcs_config.cpu_based_2nd_exec_ctrl:
> 
>   static inline bool cpu_has_vmx_encls_vmexit(void)
>   {
> 	return vmcs_config.cpu_based_2nd_exec_ctrl &
> 		SECONDARY_EXEC_ENCLS_EXITING;
>   }
> 
> And thus already incorporates this code:
> 
> 	if (!cpu_has_sgx())
> 		_cpu_based_2nd_exec_control &= ~SECONDARY_EXEC_ENCLS_EXITING;
> 
> 
> I suppose the #MC could happen between setup_vmcs_config() and
> nested_vmx_setup_ctls_msrs(), but at that point, KVM is hosed no matter what.

Exactly.  I think we can ignore this unless we can get more info from the
author :-)