Re: [RFC PATCH v3 53/59] KVM: x86: Add a helper function to restore 4 host MSRs on exit to user space

Lai Jiangshan
2021-11-30T11:18:47Z

On Tue, Nov 30, 2021 at 4:10 PM Chao Gao <chao.gao@intel.com> wrote:

>
> No, it is already documented in public spec.

In intel-tdx-module-1.5-base-spec-348549001.pdf, page 79
"recoverability hist", I think it is a "hint".

>
> TDX module spec just says some MSRs are reset to INIT state by TDX module
> (un)conditionally during TD exit. When to restore these MSRs to host's
> values is decided by host.
>

Sigh, it is quite a common solution to reset a register to a default
value here, for example in VMX, the host GDT.limit and host TSS.limit
is reset after VMEXIT, so load_fixmap_gdt() and invalidate_tss_limit()
have to be called in host in vmx_vcpu_put().

Off-topic: Is it a good idea to also put load_fixmap_gdt() and
invalidate_tss_limit() in user-return-notfier?