linux-kernel - Re: [PATCH v1 17/24] kvm: arm64: Add __hyp_pa

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Date:   Tue, 10 Nov 2020 09:24:04 +0000
From:   David Brazdil <dbrazdil@...gle.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Quentin Perret <qperret@...gle.com>, kvmarm@...ts.cs.columbia.edu,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Dennis Zhou <dennis@...nel.org>,
        Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>,
        Mark Rutland <mark.rutland@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Andrew Scull <ascull@...gle.com>,
        Andrew Walbran <qwandor@...gle.com>, kernel-team@...roid.com
Subject: Re: [PATCH v1 17/24] kvm: arm64: Add __hyp_pa_symbol helper macro

On Mon, Nov 09, 2020 at 06:10:05PM +0000, Marc Zyngier wrote:
> On 2020-11-09 16:59, Quentin Perret wrote:
> > Hey David,
> > 
> > On Monday 09 Nov 2020 at 11:32:26 (+0000), David Brazdil wrote:
> > > Add helper macro for computing the PA of a kernel symbol in nVHE hyp
> > > code. This will be useful for computing the PA of a PSCI CPU_ON entry
> > > point.
> > > 
> > > Signed-off-by: David Brazdil <dbrazdil@...gle.com>
> > > ---
> > >  arch/arm64/kvm/hyp/nvhe/psci.c | 10 ++++++++++
> > >  1 file changed, 10 insertions(+)
> > > 
> > > diff --git a/arch/arm64/kvm/hyp/nvhe/psci.c
> > > b/arch/arm64/kvm/hyp/nvhe/psci.c
> > > index b0b5df590ba5..7510b9e174e9 100644
> > > --- a/arch/arm64/kvm/hyp/nvhe/psci.c
> > > +++ b/arch/arm64/kvm/hyp/nvhe/psci.c
> > > @@ -20,6 +20,16 @@ s64 hyp_physvirt_offset;
> > > 
> > >  #define __hyp_pa(x) ((phys_addr_t)((x)) + hyp_physvirt_offset)
> > > 
> > > +#define __hyp_pa_symbol(sym)					\
> > > +	({							\
> > > +		extern char sym[];				\
> > > +		unsigned long kern_va;				\
> > > +								\
> > > +		asm volatile("ldr %0, =%1" : "=r" (kern_va)	\
> > > +					   : "S" (sym));	\
> > > +		kern_va - kimage_voffset;			\
> > > +	})
> > > +
> > 
> > Could this be simplified to __hyp_pa(hyp_symbol_addr(sym))? That would
> > avoid the dependency on kimage_voffset.

Ah, didn't see that one. Ok, removing this patch.

> 
> I'm going to move away from evaluating kimage_voffset at runtime anyway,
> see [1].

Awesome! One more dependency gone.

> 
> Thanks,
> 
>         M.
> 
> [1] https://lore.kernel.org/r/20201109175923.445945-1-maz@kernel.org
> -- 
> Jazz is not dead. It just smells funny...