linux-kernel - Re: [PATCH v4 04/15] arm64: realm: Query IPA size from the RMM

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Message-ID: <20240709105325.GF12978@willie-the-truck>
Date: Tue, 9 Jul 2024 11:53:25 +0100
From: Will Deacon <will@...nel.org>
To: Steven Price <steven.price@....com>
Cc: kvm@...r.kernel.org, kvmarm@...ts.linux.dev,
	Catalin Marinas <catalin.marinas@....com>,
	Marc Zyngier <maz@...nel.org>, James Morse <james.morse@....com>,
	Oliver Upton <oliver.upton@...ux.dev>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Joey Gouly <joey.gouly@....com>,
	Alexandru Elisei <alexandru.elisei@....com>,
	Christoffer Dall <christoffer.dall@....com>,
	Fuad Tabba <tabba@...gle.com>, linux-coco@...ts.linux.dev,
	Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>
Subject: Re: [PATCH v4 04/15] arm64: realm: Query IPA size from the RMM

On Mon, Jul 01, 2024 at 10:54:54AM +0100, Steven Price wrote:
> The top bit of the configured IPA size is used as an attribute to
> control whether the address is protected or shared. Query the
> configuration from the RMM to assertain which bit this is.
> 
> Co-developed-by: Suzuki K Poulose <suzuki.poulose@....com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> Signed-off-by: Steven Price <steven.price@....com>
> ---
> Changes since v2:
>  * Drop unneeded extra brackets from PROT_NS_SHARED.
>  * Drop the explicit alignment from 'config' as struct realm_config now
>    specifies the alignment.
> ---
>  arch/arm64/include/asm/pgtable-prot.h | 3 +++
>  arch/arm64/kernel/rsi.c               | 8 ++++++++
>  2 files changed, 11 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h
> index b11cfb9fdd37..6c29f3b32eba 100644
> --- a/arch/arm64/include/asm/pgtable-prot.h
> +++ b/arch/arm64/include/asm/pgtable-prot.h
> @@ -70,6 +70,9 @@
>  #include <asm/pgtable-types.h>
>  
>  extern bool arm64_use_ng_mappings;
> +extern unsigned long prot_ns_shared;
> +
> +#define PROT_NS_SHARED		(prot_ns_shared)

Since the _vast_ majority of Linux systems won't be running in a realm,
can we use a static key to avoid loading a constant each time?

Will