linux-kernel - Re: [PATCH 2/2] KVM: SVM: add some info prints to SEV init

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Message-ID: <ZGfj0QrdgQDhrR0M@google.com>
Date:   Fri, 19 May 2023 14:02:09 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Aleksandr Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
Cc:     pbonzini@...hat.com,
        "Stéphane Graber" <stgraber@...ntu.com>,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] KVM: SVM: add some info prints to SEV init

On Fri, May 19, 2023, Aleksandr Mikhalitsyn wrote:
> On Fri, May 19, 2023 at 8:17 PM Sean Christopherson <seanjc@...gle.com> wrote:
> >
> > On Tue, Apr 04, 2023, Alexander Miqqqqkhalitsyn wrote:
> > > Let's add a few pr_info's to sev_hardware_setup to make SEV/SEV-ES
> > > enabling a little bit handier for users. Right now it's too hard
> > > to guess why SEV/SEV-ES are failing to enable.
> >
> > Hmm, I'm somewhat torn, but I'm against taking this patch, at least not in its
> > current form.  I appreciated that determining why KVM isn't enabling SEV/SEV-ES
> > is annoying, but there's very little actionable information provided here that
> > isn't also super obvious.  I also don't want to start us down a slippery slope
> > of printing out messages every time KVM doesn't enable a feature.
> >
> > If someone tries to enable SEV and doesn't check that their CPU supports SEV,
> > then IMO that's on them.  Ditto for SEV-ES.
> >
> > The NPT thing is mildly interesting, but practically speaking I don't expect that
> > to ever be a hindrace for generic enabling.  Ditto for MMIO caching.
> >
> > The decode assists check is (a) completely unactionable for the vast, vast majority
> > of users and (b) is a WARN_ON_ONCE() condition.
> >
> > The ASID stuff is by far the most interesting, but that's also quite interesting
> > for when SEV and SEV-ES _are_ fully supported.
> >
> > So if we want to provide the user more info, I'd prefer to do something like the
> > below, which I think would be more helpful and would avoid my slippery slope
> > concerns.
> 
> Dear Sean,
> 
> Thanks for looking into this!
> 
> I agree with your points, let's go that way and print only ASID stuff
> as it can be not obvious to the end-user.
> 
> I'm ready to prepare -v2 if you don't mind.

Ya, fire away.  Thanks!