linux-kernel - Re: [PATCH v2] KVM: allow KVM_BUG/KVM_BUG

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Date:   Fri, 2 Jun 2023 09:56:52 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Michal Luczaj <mhal@...x.co>
Cc:     dmatlack@...gle.com, mizhang@...gle.com, isaku.yamahata@...il.com,
        pbonzini@...hat.com, Wei Wang <wei.w.wang@...el.com>,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] KVM: allow KVM_BUG/KVM_BUG_ON to handle 64-bit cond

On Fri, Jun 02, 2023, Michal Luczaj wrote:
> On 6/2/23 03:20, Sean Christopherson wrote:
> > On Tue, 07 Mar 2023 21:52:33 +0800, Wei Wang wrote:
> >> Current KVM_BUG and KVM_BUG_ON assume that 'cond' passed from callers is
> >> 32-bit as it casts 'cond' to the type of int. This will be wrong if 'cond'
> >> provided by a caller is 64-bit, e.g. an error code of 0xc0000d0300000000
> >> will be converted to 0, which is not expected.
> >>
> >> Improves the implementation by using bool in KVM_BUG and KVM_BUG_ON.
> >> 'bool' is preferred to 'int' as __ret is essentially used as a boolean
> >> and coding-stytle.rst documents that use of bool is encouraged to improve
> >> readability and is often a better option than 'int' for storing boolean
> >> values.
> >>
> >> [...]
> > 
> > Applied to kvm-x86 generic, thanks!
> > 
> > [1/1] KVM: allow KVM_BUG/KVM_BUG_ON to handle 64-bit cond
> >       https://github.com/kvm-x86/linux/commit/c9d601548603
> 
> I guess this makes the !! in kvm_vm_ioctl_create_vcpu() unnecessary:
> 
> KVM_BUG_ON(!!xa_store(&kvm->vcpu_array, vcpu->vcpu_idx, vcpu, 0)...

Ya, I saw that, which in addition to Wei's ping, is what reminded me that the
KVM_BUG_ON() fix hadn't been merged.

> Is it worth a patch (perhaps along with chopping off !! in
> kvm_msr_allowed() and few other places)?

Yes, I think so.