linux-kernel - Re: [PATCH v3 15/21] KVM: arm64: Introduce addr_is

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Message-ID: <YQkZMyyqgqb8+Uqq@google.com>
Date:   Tue, 3 Aug 2021 11:23:47 +0100
From:   Quentin Perret <qperret@...gle.com>
To:     Fuad Tabba <tabba@...gle.com>
Cc:     maz@...nel.org, james.morse@....com, alexandru.elisei@....com,
        suzuki.poulose@....com, catalin.marinas@....com, will@...nel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org, ardb@...nel.org, qwandor@...gle.com,
        dbrazdil@...gle.com, kernel-team@...roid.com
Subject: Re: [PATCH v3 15/21] KVM: arm64: Introduce addr_is_memory()

On Monday 02 Aug 2021 at 16:52:31 (+0200), Fuad Tabba wrote:
> Hi Quentin.
> 
> On Thu, Jul 29, 2021 at 3:28 PM Quentin Perret <qperret@...gle.com> wrote:
> >
> > Introduce a helper usable in nVHE protected mode to check whether a
> > physical address is in a RAM region or not.
> >
> > Signed-off-by: Quentin Perret <qperret@...gle.com>
> > ---
> >  arch/arm64/kvm/hyp/include/nvhe/mem_protect.h | 1 +
> >  arch/arm64/kvm/hyp/nvhe/mem_protect.c         | 7 +++++++
> >  2 files changed, 8 insertions(+)
> >
> > diff --git a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> > index cc86598654b9..5968fbbb3514 100644
> > --- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> > +++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> > @@ -51,6 +51,7 @@ extern const u8 pkvm_hyp_id;
> >  int __pkvm_prot_finalize(void);
> >  int __pkvm_mark_hyp(phys_addr_t start, phys_addr_t end);
> >
> > +bool addr_is_memory(phys_addr_t phys);
> 
> I'm just wondering about the naming of the function. I understand what
> you're trying to achieve with it, but an address without a unit that
> conveys size or type seems to be missing something. Would

Well it does have a type no? I was hopping this would make it clear what
it actually does.

> memregion_addr_is_memory or something like that be a better
> description, since it is what find_mem_range finds?

I think the callers shouldn't need to care about the implementation
details though. This just replies to the question 'is this physical
address in RAM range or not?'. And I could actually imagine that we
would change the implementation some day to avoid the binary search, but
the users probably don't need to care.

Thanks,
Quentin