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Date:   Sat, 18 Jun 2022 00:09:11 +0000
From:   Sean Christopherson <seanjc@google.com>
To:     Colton Lewis <coltonlewis@google.com>
Cc:     Andrew Jones <drjones@redhat.com>, kvm@vger.kernel.org,
        kvmarm@lists.cs.columbia.edu, pbonzini@redhat.com,
        vkuznets@redhat.com, thuth@redhat.com, maz@kernel.org
Subject: Re: [PATCH 2/4] KVM: selftests: Increase UCALL_MAX_ARGS to 7
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References: <20220615193116.806312-1-coltonlewis@google.com>
 <20220615193116.806312-3-coltonlewis@google.com>
 <20220616121006.ch6x7du6ycevjo5m@gator>
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On Fri, Jun 17, 2022, Colton Lewis wrote:
> On Thu, Jun 16, 2022 at 02:10:06PM +0200, Andrew Jones wrote:
> > We probably want to ensure all architectures are good with this. afaict,
> > riscv only expects 6 args and uses UCALL_MAX_ARGS to cap the ucall inputs,
> > for example.
> 
> All architectures use UCALL_MAX_ARGS for that. Are you saying there
> might be limitations beyond the value of the macro? If so, who should
> verify whether this is ok?

I thought there were architectural limitations too, but I believe I was thinking
of vcpu_args_set(), where the number of params is limited by the function call
ABI, e.g. the number of registers.

Unless there's something really, really subtle going on, all architectures pass
the actual ucall struct purely through memory.  Actually, that code is ripe for
deduplication, and amazingly it doesn't conflict with Colton's series.  Patches
incoming...