Re: [PATCHv2 28/29] x86/tdx: Warn about unexpected WBINVD

Kirill A. Shutemov
2022-02-04T21:35:52Z

On Wed, Feb 02, 2022 at 02:46:17AM +0100, Thomas Gleixner wrote:
> On Mon, Jan 24 2022 at 18:02, Kirill A. Shutemov wrote:
>
> > WBINVD causes #VE in TDX guests. There's no reliable way to emulate it.
> > The kernel can ask for VMM assistance, but VMM is untrusted and can ignore
> > the request.
> >
> > Fortunately, there is no use case for WBINVD inside TDX guests.
>
> If there is not usecase, then why
>
> > Warn about any unexpected WBINVD.
>
> instead of terminating the whole thing?
>
> I'm tired of the "let us emit a warning in the hope it gets fixed'
> thinking.

I probably misunderstood what you meant in the previous WBINVD thread[1] by:

Then you have the #VE handler which just acts on any other wbinvd
invocation via warn, panic, whatever, no?

I went the warn path because I think it is consistent with BUG() vs. WARN()
policy: "Use WARN() and WARN_ON() instead, and handle the "impossible"
error condition as gracefully as possible."[2]

IMO, ignored WBINVD has less chance to lead user data loss than panic().

Anyway, I'm okay dropping the patch. It will bring us to "terminate whole
thing" solution. I just wanted to explain why the patch is present in the
series.

[1] https://lore.kernel.org/all/87lf126010.ffs@tglx/
[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/deprecated.rst

--
Kirill A. Shutemov