Re: [PATCH RFC 1/3] x86/kvm/vmx: read MSR_FS_BASE from current->thread

[Andy Lutomirski]

On Fri, Mar 2, 2018 at 10:55 AM, Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> wrote:
> vmx_save_host_state() is only called from kvm_arch_vcpu_ioctl_run() so
> the context is pretty well defined
>

True.

> and MSR_FS_BASE should always be
> equal to current->thread.fsbase.

Not true.  current->thread.fsbase is almost entirely undefined in this
context.  What you *could* do is export save_fsgs() and call it first.
When FSGSBASE support lands (which will happen eventually!), the code
in your patch will be completely wrong.

Admittedly, your patch isn't 100% bogus, but the reason is subtle and
you need lots of comments there *and* in save_fsgs().