Re: [Xen-devel] [PATCH v2] libxc/x86: avoid overflow in CPUID APIC ID adjustments

[Jan Beulich <jbeulich@xxxxxxxx>]

On 20.09.2019 15:54, Jan Beulich wrote:
> Recent AMD processors may report up to 128 logical processors in CPUID
> leaf 1. Doubling this value produces 0 (which OSes sincerely dislike),
> as the respective field is only 8 bits wide. Suppress doubling the value
> (and its leaf 0x80000008 counterpart) in such a case.
> 
> Note that while there's a similar overflow in intel_xc_cpuid_policy(),
> that one is being left alone for now.
> 
> Note further that while it was considered to suppress the multiplication
> by 2 altogether if the host topology already provides at least one bit
> of thread ID within APIC IDs, it was decided to avoid more change here
> than really needed at this point.

Given this I've just changed the title to "avoid certain overflows in
CPUID APIC ID adjustments".

Jan

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