Re: [PATCH 23/27] arm64/sve: KVM: Hide SVE from CPU features exposed to guests

Dave Martin
2017-08-16T11:22:34Z

On Wed, Aug 16, 2017 at 12:10:53PM +0100, Marc Zyngier wrote:
> On 16/08/17 11:54, Dave Martin wrote:
> > On Tue, Aug 15, 2017 at 05:37:55PM +0100, Marc Zyngier wrote:
> >> On 09/08/17 13:05, Dave Martin wrote:

[...]

> >>> + if (id == SYS_ID_AA64PFR0_EL1) {
> >>> + static bool printed;
> >>> +
> >>> + if ((val & (0xfUL << ID_AA64PFR0_SVE_SHIFT)) && !printed) {
> >>> + kvm_info("SVE unsupported for guests, suppressing\n");
> >>> + printed = true;
> >>> + }
> >>
> >> Ideally, this should be a vcpu_unimpl_once(). But:
> >> - it doesn't exist
> >> - vcpu_unimpl looks hopelessly x86 specific
> >
> > Yeah, I looked for an appropriate function and didn't find one ... and
> > writing one just for this seemed overkill.
> >
> >> How about turning it into a pr_err_once() instead?
> >
> > Can do, though should it be an err?
> >
> > No error has occurred here, rather I want people who discover that their
> > guest mysteriously doesn't see SVE gets a clue about why.
> An "err" is a good way to make it appear on the console. If you want to
> make it noticed, that's the way.

OK, I was concerned that overuse of err might be frowned upon.

If this is the preferred way to signal such things, I'm happy to that.

Cheers
---Dave