Re: [PATCH 02/12] x86: Add more granularity to the vendors in Kconfig

[Jan Beulich <jbeulich@xxxxxxxx>]

On 11.02.2026 18:51, Alejandro Vallejo wrote:
> On Wed Feb 11, 2026 at 5:06 PM CET, Jan Beulich wrote:
>> On 06.02.2026 17:15, Alejandro Vallejo wrote:
>>> --- a/xen/arch/x86/Kconfig.cpu
>>> +++ b/xen/arch/x86/Kconfig.cpu
>>> @@ -19,4 +19,47 @@ config INTEL
>>>       May be turned off in builds targetting other vendors.  Otherwise,
>>>       must be enabled for Xen to work suitably on Intel platforms.
>>>  
>>> +config HYGON
>>> +   bool "Support Hygon CPUs"
>>> +   select AMD
>>> +   default y
>>> +   help
>>> +     Detection, tunings and quirks for Hygon platforms.
>>> +
>>> +     May be turned off in builds targetting other vendors.  Otherwise,
>>> +     must be enabled for Xen to work suitably on Hygon platforms.
>>> +
>>> +
>>> +config CENTAUR
>>> +   bool "Support Centaur CPUs"
>>> +   select INTEL
>>> +   default y
>>> +   help
>>> +     Detection, tunings and quirks for Centaur platforms.
>>> +
>>> +     May be turned off in builds targetting other vendors.  Otherwise,
>>> +     must be enabled for Xen to work suitably on Centaur platforms.
>>> +
>>> +config SHANGHAI
>>> +   bool "Support Shanghai CPUs"
>>> +   select INTEL
>>> +   default y
>>> +   help
>>> +     Detection, tunings and quirks for Shanghai platforms.
>>> +
>>> +     May be turned off in builds targetting other vendors.  Otherwise,
>>> +     must be enabled for Xen to work suitably on Shanghai platforms.
>>> +
>>> +config UNKNOWN_CPU_VENDOR
>>> +   bool "Support unknown CPU vendors"
>>> +   default y
>>> +   help
>>> +     This option prevents a panic on boot when the host CPU vendor isn't
>>> +     supported by going into a legacy compatibility mode and not applying
>>> +     any relevant tunings or quirks.
>>> +
>>> +     Not selecting this options while selecting multiple vendors doesn't 
>>> have
>>> +     any major effect on code size, but selecting a single vendor with this
>>> +     option cleared produces a much smaller build.
>>
>> Shouldn't this option's prompt be suppressed when all other vendors were
>> selected off? Else the degenerate case can result that I mentioned in
>> reply to patch 03.
> 
> You mean having the option disappear when any explicit vendor is enabled?

No, I mean the prompt (not the option) to disappear when _no_ explicit
vendor is enabled. Because of the select-s above, that could effectively
be as simple as

config UNKNOWN_CPU_VENDOR
        bool "Support unknown CPU vendors" if INTEL || AMD
        default y

Otherwise, as indicated, the conditional around the panic() in patch 03
degenerates: The panic() would be skipped despite UNKNOWN_CPU_VENDOR=n,
as with X86_ENABLED_VENDORS being 0, cpu_vendor() can't tell
UNKNOWN_CPU_VENDOR=n from UNKNOWN_CPU_VENDOR=y.

Jan