linux-kernel - Re: [PATCH v3 06/14] arm64: Override set_fixmap

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Message-ID: <Zmc8x3Xvs8uu9zHp@arm.com>
Date: Mon, 10 Jun 2024 18:49:59 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Steven Price <steven.price@....com>
Cc: kvm@...r.kernel.org, kvmarm@...ts.linux.dev,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>,
	James Morse <james.morse@....com>,
	Oliver Upton <oliver.upton@...ux.dev>,
	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 v3 06/14] arm64: Override set_fixmap_io

On Wed, Jun 05, 2024 at 10:29:58AM +0100, Steven Price wrote:
> +void set_fixmap_io(enum fixed_addresses idx, phys_addr_t phys)
> +{
> +	pgprot_t prot = FIXMAP_PAGE_IO;
> +
> +	/*
> +	 * For now we consider all I/O as non-secure. For future
> +	 * filter the I/O base for setting appropriate permissions.
> +	 */
> +	prot = __pgprot(pgprot_val(prot) | PROT_NS_SHARED);
> +
> +	return __set_fixmap(idx, phys, prot);
> +}

In v2, Suzuki said that we want to keep this as a function rather than
just adding PROT_NS_SHARED to FIXMAP_PAGE_IO in case we want to change
this function in the future to allow protected MMIO.

https://lore.kernel.org/linux-arm-kernel/6ba1fd72-3bad-44ca-810d-572b70050772@arm.com/

What I don't understand is that all the other MMIO cases just statically
assume unprotected/shard MMIO. Should we drop this patch here as well,
adjust FIXMAP_PAGE_IO and think about protected MMIO later when we
actually have to do device assignment?

-- 
Catalin