Re: [PATCH v5] x86: detect CMOS aliasing on ports other than 0x70/0x71

[Jan Beulich <jbeulich@xxxxxxxx>]

On 03.04.2023 13:44, Roger Pau Monné wrote:
> On Mon, Apr 03, 2023 at 01:26:41PM +0200, Jan Beulich wrote:
>> On 03.04.2023 13:09, Roger Pau Monné wrote:
>>> On Thu, Mar 30, 2023 at 12:40:38PM +0200, Jan Beulich wrote:
>>>> +bool is_cmos_port(unsigned int port, unsigned int bytes, const struct 
>>>> domain *d)
>>>> +{
>>>> +    unsigned int offs;
>>>> +
>>>> +    if ( !is_hardware_domain(d) ||
>>>> +         !(acpi_gbl_FADT.boot_flags & ACPI_FADT_NO_CMOS_RTC) )
>>>> +        return port <= RTC_PORT(1) && port + bytes > RTC_PORT(0);
>>>> +
>>>> +    if ( acpi_gbl_FADT.boot_flags & ACPI_FADT_NO_CMOS_RTC )
>>>> +        return false;
>>>> +
>>>> +    for ( offs = 2; offs <= cmos_alias_mask; offs <<= 1 )
>>>> +    {
>>>> +        if ( !(offs & cmos_alias_mask) )
>>>> +            continue;
>>>> +        if ( port <= RTC_PORT(offs | 1) && port + bytes > RTC_PORT(offs) )
>>>> +            return true;
>>>> +    }
>>>
>>> Maybe I'm confused, but doesn't this loop start at RTC_PORT(2), and
>>> hence you need to check for the RTC_PORT(0,1) pair outside of the
>>> loop?
>>
>> The loop starts at offset 2, yes, but see the initial if() in the
>> function. Or at least I thought I got that right, but it looks like
>> I didn't (failed attempt to try to address a specific request of
>> yours, iirc).
> 
> Hm, doesn't that first if() cause that on all systems with an RTC only
> PORTS(0,1) are allowed?

Indeed, hence why I said "failed attempt". Looking at it now I really
don't know what I was thinking when writing it that way.

Jan