Re: [PATCH v15 21/41] KVM: nVMX: Prepare for enabling CET support for nested guest

Xin Li
2025-09-18T04:48:22Z

On 9/12/2025 4:22 PM, Sean Christopherson wrote:
> diff --git a/arch/x86/kvm/vmx/vmcs12.h b/arch/x86/kvm/vmx/vmcs12.h
> index 56fd150a6f24..4ad6b16525b9 100644
> --- a/arch/x86/kvm/vmx/vmcs12.h
> +++ b/arch/x86/kvm/vmx/vmcs12.h
> @@ -117,7 +117,13 @@ struct __packed vmcs12 {
> natural_width host_ia32_sysenter_eip;
> natural_width host_rsp;
> natural_width host_rip;
> - natural_width paddingl[8]; /* room for future expansion */
> + natural_width host_s_cet;
> + natural_width host_ssp;
> + natural_width host_ssp_tbl;
> + natural_width guest_s_cet;
> + natural_width guest_ssp;
> + natural_width guest_ssp_tbl;
> + natural_width paddingl[2]; /* room for future expansion */
> u32 pin_based_vm_exec_control;
> u32 cpu_based_vm_exec_control;
> u32 exception_bitmap;
> @@ -294,6 +300,12 @@ static inline void vmx_check_vmcs12_offsets(void)
> CHECK_OFFSET(host_ia32_sysenter_eip, 656);
> CHECK_OFFSET(host_rsp, 664);
> CHECK_OFFSET(host_rip, 672);
> + CHECK_OFFSET(host_s_cet, 680);
> + CHECK_OFFSET(host_ssp, 688);
> + CHECK_OFFSET(host_ssp_tbl, 696);
> + CHECK_OFFSET(guest_s_cet, 704);
> + CHECK_OFFSET(guest_ssp, 712);
> + CHECK_OFFSET(guest_ssp_tbl, 720);
> CHECK_OFFSET(pin_based_vm_exec_control, 744);
> CHECK_OFFSET(cpu_based_vm_exec_control, 748);
> CHECK_OFFSET(exception_bitmap, 752);

This patch modifies struct vms12 without updating the corresponding vmcs12
definition in Documentation/virt/kvm/x86/nested-vmx.rst. However,
duplicating the definition within the same source tree seems unnecessary
and prone to inconsistencies. E.g., the following fields are missing in
Documentation/virt/kvm/x86/nested-vmx.rst:

...
u64 posted_intr_desc_addr;
...
u64 eoi_exit_bitmap0;
u64 eoi_exit_bitmap1;
u64 eoi_exit_bitmap2;
u64 eoi_exit_bitmap3;
u64 xss_exit_bitmap;
...

What's more, the 64-bit padding fields are completely messed up; we have
used 9 u64 after host_ia32_efer:

u64 host_ia32_perf_global_ctrl;
u64 vmread_bitmap;
u64 vmwrite_bitmap;
u64 vm_function_control;
u64 eptp_list_address;
u64 pml_address;
u64 encls_exiting_bitmap;
u64 tsc_multiplier;
u64 padding64[1]; /* room for future expansion */

But it's 8 u64 after host_ia32_efer in the documentation:

u64 padding64[8]; /* room for future expansion */

We probably should remove it from Documentation/virt/kvm/x86/nested-vmx.rst
and instead add a reference to arch/x86/kvm/vmx/vmcs12.h.