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

[Wei Liu <wl@xxxxxxx>]

On Fri, Sep 20, 2019 at 03:54:12PM +0200, 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.
> 
> Also zap leaf 4 (and at the same time leaf 2) EDX output for AMD, as it
> should have been from the beginning.
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

I'm going to defer this patch to Andrew.

Wei.

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