Re: [PATCH v2] KVM: nVMX: Sync L2 guest CET states between L1/L2

Vitaly Kuznetsov
2021-03-02T11:02:24Z

Sean Christopherson <seanjc@google.com> writes:

> +Vitaly
>
> On Thu, Feb 25, 2021, Yang Weijiang wrote:
>> These fields are rarely updated by L1 QEMU/KVM, sync them when L1 is trying to
>> read/write them and after they're changed. If CET guest entry-load bit is not
>> set by L1 guest, migrate them to L2 manaully.
>>
>> Suggested-by: Sean Christopherson <seanjc@google.com>
>> Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
>>
>> change in v2:
>> - Per Sean's review feedback, change CET guest states as rarely-updated fields.
>> And also migrate L1's CET states to L2 if the entry-load bit is not set.
>> - Opportunistically removed one blank line.
>> ---
>> arch/x86/kvm/cpuid.c | 1 -
>> arch/x86/kvm/vmx/nested.c | 29 +++++++++++++++++++++++++++++
>> arch/x86/kvm/vmx/vmx.h | 3 +++
>> 3 files changed, 32 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
>> index 46087bca9418..afc97122c05c 100644
>> --- a/arch/x86/kvm/cpuid.c
>> +++ b/arch/x86/kvm/cpuid.c
>> @@ -143,7 +143,6 @@ void kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu)
>> }
>> vcpu->arch.guest_supported_xss =
>> (((u64)best->edx << 32) | best->ecx) & supported_xss;
>> -
>> } else {
>> vcpu->arch.guest_supported_xss = 0;
>> }
>> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
>> index 9728efd529a1..1703b8874fad 100644
>> --- a/arch/x86/kvm/vmx/nested.c
>> +++ b/arch/x86/kvm/vmx/nested.c
>> @@ -2516,6 +2516,12 @@ static void prepare_vmcs02_rare(struct vcpu_vmx *vmx, struct vmcs12 *vmcs12)
>> vmcs_write32(VM_ENTRY_MSR_LOAD_COUNT, vmx->msr_autoload.guest.nr);
>>
>> set_cr4_guest_host_mask(vmx);
>> +
>> + if (kvm_cet_supported()) {
>
> This needs to be conditioned on CET coming from vmcs12, it's on the loading of
> host state on VM-Exit that is unconditional (if CET is supported).
>
> if (kvm_cet_supported() && vmx->nested.nested_run_pending &&
> (vmcs12->vm_entry_controls & VM_ENTRY_LOAD_CET_STATE)) {
>
> I also assume these should be guarded by one of the eVMCS fields, though a quick
> search of the public docs didn't provide a hit on the CET fields.
>
> Vitaly, any idea if these will be GUEST_GRP2 or something else?
>

The latest published TLFS I see is 6.0b and it doesn't list anything CET
related in eVMCS v1.0 :-( So I agree with Paolo: we just need to adjust
EVMCS1_UNSUPPORTED_VMENTRY_CTRL/ EVMCS1_UNSUPPORTED_VMEXIT_CTRL for now
and enable it separately later.

>> + vmcs_writel(GUEST_SSP, vmcs12->guest_ssp);
>> + vmcs_writel(GUEST_S_CET, vmcs12->guest_s_cet);
>> + vmcs_writel(GUEST_INTR_SSP_TABLE, vmcs12->guest_ssp_tbl);
>> + }
>> }
>

--
Vitaly