Re: [PATCH v16 24/51] KVM: nVMX: Always forward XSAVES/XRSTORS exits from L2 to L1

Chao Gao
2025-09-23T08:16:11Z

On Fri, Sep 19, 2025 at 03:32:31PM -0700, Sean Christopherson wrote:
>Unconditionally forward XSAVES/XRSTORS VM-Exits from L2 to L1, as KVM
>doesn't utilize the XSS-bitmap (KVM relies on controlling the XSS value
>in hardware to prevent unauthorized access to XSAVES state). KVM always
>loads vmcs02 with vmcs12's bitmap, and so any exit _must_ be due to
>vmcs12's XSS-bitmap.
>
>Drop the comment about XSS never being non-zero in anticipation of
>enabling CET_KERNEL and CET_USER support.
>
>Opportunistically WARN if XSAVES is not enabled for L2, as the CPU is
>supposed to generate #UD before checking the XSS-bitmap.
>
>Signed-off-by: Sean Christopherson <seanjc@google.com>

Reviewed-by: Chao Gao <chao.gao@intel.com>