linux-kernel - Re: [PATCH 01/15] arm64: kvm: Unify users of HVC instruction

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Date:   Thu, 7 May 2020 15:36:33 +0100
From:   Quentin Perret <qperret@...gle.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     David Brazdil <dbrazdil@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Will Deacon <will@...nel.org>, kvmarm@...ts.cs.columbia.edu,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/15] arm64: kvm: Unify users of HVC instruction

On Thursday 07 May 2020 at 15:01:07 (+0100), Marc Zyngier wrote:
> >  /*
> > - * u64 __kvm_call_hyp(void *hypfn, ...);
> > + * u64 __kvm_call_hyp(unsigned long arg, ...);
> >   *
> >   * This is not really a variadic function in the classic C-way and care must
> >   * be taken when calling this to ensure parameters are passed in registers
> >   * only, since the stack will change between the caller and the callee.
> > - *
> > - * Call the function with the first argument containing a pointer to the
> > - * function you wish to call in Hyp mode, and subsequent arguments will be
> > - * passed as x0, x1, and x2 (a maximum of 3 arguments in addition to the
> > - * function pointer can be passed).  The function being called must be mapped
> > - * in Hyp mode (see init_hyp_mode in arch/arm/kvm/arm.c).  Return values are
> > - * passed in x0.
> > - *
> > - * A function pointer with a value less than 0xfff has a special meaning,
> > - * and is used to implement hyp stubs in the same way as in
> > - * arch/arm64/kernel/hyp_stub.S.
> 
> I don't think any of this becomes obsolete with this patch (apart from
> the reference to 32bit), and only changes with patch #2. Or am I
> misunderstanding something?

Nope, I think you're right. To be fair, this patch has changed quite
a bit since the first version (which did change that comment a little
later IIRC), but David has done all the hard work on top so I'll let
him answer that one.

And David, feel free to take the authorship for this patch -- I barely
recognize it (for the better), so it's more than fair if you get the
credit :)

Thanks,
Quentin