linux-kernel - Re: [PATCH v2 06/14] arm64: Override set_fixmap

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Date: Tue, 14 May 2024 11:21:40 +0100
From: Suzuki K Poulose <suzuki.poulose@....com>
To: Catalin Marinas <catalin.marinas@....com>,
 Steven Price <steven.price@....com>
Cc: kvm@...r.kernel.org, kvmarm@...ts.linux.dev, 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 v2 06/14] arm64: Override set_fixmap_io

On 13/05/2024 17:14, Catalin Marinas wrote:
> On Fri, Apr 12, 2024 at 09:42:05AM +0100, Steven Price wrote:
>> Override the set_fixmap_io to set shared permission for the host
>> in case of a CC guest. For now we mark it shared unconditionally.
>> Future changes could filter the physical address and make the
>> decision accordingly.
> [...]
>> +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);
>> +}
> 
> I looked through the patches and could not find any place where this
> function does anything different as per the commit log suggestion. Can
> we just update FIXMAP_PAGE_IO for now until you have a clear use-case?
> 

This gets used by the earlycon mapping. The commit description could be
made clear.

We may have to revisit this code to optionally apply the PROT_NS_SHARED
attribute, depending on whether this is a "protected MMIO" or not.


Suzuki