Re: [PATCH] x86/resctrl: Require force for L3 CAT on early Skylake-X

[Graf (AWS), Alexander]

Hi Tony,

On 15.10.26 19:11, Luck, Tony wrote:
> On Thu, Oct 15, 2026 at 04:58:46PM +0000, Graf (AWS), Alexander wrote:
>> I ran a few more experiments. This seems un- or if anything only mildly
>> related to kexec. The real culprit is the microcode version. In my
>> environment, we boot with older microcode (0x1000159), then hot load the
>> latest microcode (0x1000191) and then kexec. In that flow, any write to
>> IA32_L3_QOS_MASK_n stalls the socket that write happens on. I'm
>> collecting a bit more data - including microcode version bisects, early
>> load, etc - and give you a full rundown tomorrow or on Monday, depending
>> on how quickly it finishes.
> Alexander,
>
> I don't think that an upstream generic kernel solution is the right
> path for your very system-specific issue.
>
> Can't you fix your deployment scripts to look at system stepping and
> use that to choose the kernel boot options? I presume that you already
> have checks for CPU model number since there are lots of different
> options appropriate on a per-model basis. So adding a stepping check
> may be easier than battling upstream Linux submission process.


I can hack around it for my specific environment. The reason I'm 
submitting this is because I expect that I won't be the only person 
falling into that pitfall. I expect that early microcode loading (which 
is distro default) would show the same failure without kexec. I want to 
save the next person that runs into it the same painful debugging 
exercise :).


Alex