Re: [PATCH v2 0/6] KVM/x86: Drop "1" as MSR emulation return value

[Jürgen Groß]

On 28.05.26 17:32, David Woodhouse wrote:
> On Thu, 2026-05-28 at 16:33 +0200, Jürgen Groß wrote:
> > On 28.05.26 15:21, Sean Christopherson wrote:
> > > On Thu, May 28, 2026, Jürgen Groß wrote:
> > > > On 28.05.26 15:09, Sean Christopherson wrote:
> > > > > On Thu, May 28, 2026, Juergen Gross wrote:
> > > > > > Please disregard this series, there is one complication sashiko made me
> > > > > > aware of.
> > > > >
> > > > > Sashiko beat me to the punch. :-)
> > > > >
> > > > > See commit 2368048bf5c2 ("KVM: x86: Signal #GP, not -EPERM, on bad WRMSR(MCi_CTL/STATUS)")
> > > > > for a real world example of how things can and will go wrong.
> > > >
> > > > Yeah, with Sashiko's pointer it was easy to spot.
> > > >
> > > > Question now is whether the already existing cases of -errno passed as return
> > > > value are wrong or on purpose.
> > >
> > > What are the existing cases?
> >
> > Found another one:
> >
> > kvm_xen_write_hypercall_page() (called by kvm_set_msr_common())
>
> You mean in the case where it's using the user-provided hypercall page,
> and can't copy from the buffer that the VMM provided?

Yes.

> I think that's correct to return -errno via PTR_ERR() and let the guest
> die?

In this case I think a comment in this regard would be nice, as it would
prevent others stumbling over it asking the same question again.


Juergen

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