linux-kernel - Re: [PATCH v10 16/19] KVM: xen: split up kvm_xen_set_evtchn

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Message-ID: <ad800a830dab3cdefc28e30aa0b59fa5b4ba0211.camel@infradead.org>
Date:   Thu, 14 Dec 2023 14:20:27 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Paul Durrant <paul@....org>, Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Sean Christopherson <seanjc@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, Shuah Khan <shuah@...nel.org>,
        kvm@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v10 16/19] KVM: xen: split up kvm_xen_set_evtchn_fast()

On Thu, 2023-12-14 at 14:00 +0000, David Woodhouse wrote:
> 
> > +       if (IS_ENABLED(CONFIG_64BIT) && kvm->arch.xen.long_mode) {
> > +               struct vcpu_info *vcpu_info = gpc->khva;
> > +               u32 port_word_bit = port / 32;
> 
> Shouldn't that one be /64, and the compat one be /32?

I think the reason the test failed to spot this for you is because...

#define EVTCHN_TEST1 15
#define EVTCHN_TEST2 66
#define EVTCHN_TIMER 13

... it doesn't actually use any port numbers where the bit# differs for
32-bit vs. 64-bit.

If you change EVTCHN_TIMER to something like 50, I bet it'll fail (as
it should).

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