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

Sean Christopherson
2021-03-01T22:43:04Z

+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?

> + 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);
> + }
> }