Re: [PATCH v9 23/27] KVM: VMX: Set host constant supervisor states to VMCS fields

[Yang, Weijiang]

On 1/26/2024 2:31 PM, Chao Gao wrote:
> On Tue, Jan 23, 2024 at 06:41:56PM -0800, Yang Weijiang wrote:
> > Save constant values to HOST_{S_CET,SSP,INTR_SSP_TABLE} field explicitly.
> > Kernel IBT is supported and the setting in MSR_IA32_S_CET is static after
> > post-boot(The exception is BIOS call case but vCPU thread never across it)
> > and KVM doesn't need to refresh HOST_S_CET field before every VM-Enter/
> > VM-Exit sequence.
> >
> > Host supervisor shadow stack is not enabled now and SSP is not accessible
> > to kernel mode, thus it's safe to set host IA32_INT_SSP_TAB/SSP VMCS field
> > to 0s. When shadow stack is enabled for CPL3, SSP is reloaded from PL3_SSP
> > before it exits to userspace. Check SDM Vol 2A/B Chapter 3/4 for SYSCALL/
> > SYSRET/SYSENTER SYSEXIT/RDSSP/CALL etc.
> >
> > Prevent KVM module loading if host supervisor shadow stack SHSTK_EN is set
> > in MSR_IA32_S_CET as KVM cannot co-exit with it correctly.
> >
> > Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> > Suggested-by: Chao Gao <chao.gao@xxxxxxxxx>
> > Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
> > Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
> Reviewed-by: Chao Gao <chao.gao@xxxxxxxxx>
>
> two nits below.
>
> > ---
> > arch/x86/kvm/vmx/capabilities.h |  4 ++++
> > arch/x86/kvm/vmx/vmx.c          | 15 +++++++++++++++
> > arch/x86/kvm/x86.c              | 14 ++++++++++++++
> > arch/x86/kvm/x86.h              |  1 +
> > 4 files changed, 34 insertions(+)
> >
> > diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
> > index 41a4533f9989..ee8938818c8a 100644
> > --- a/arch/x86/kvm/vmx/capabilities.h
> > +++ b/arch/x86/kvm/vmx/capabilities.h
> > @@ -106,6 +106,10 @@ static inline bool cpu_has_load_perf_global_ctrl(void)
> > 	return vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL;
> > }
> >
> > +static inline bool cpu_has_load_cet_ctrl(void)
> s/cet_ctrl/cet_state
>
> > +{
> > +	return (vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_CET_STATE);
> nit: unnecessary brackets.

OK, will fix these nits.