Re: [PATCH v2 06/14] arm64: Override set_fixmap_io

Suzuki K Poulose
2024-05-14T10:21:44Z

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