Re: [PATCH RFC] x86/cpu: fix intermittent lockup on poweroff

[Dave Hansen]

On 4/26/23 10:51, Tom Lendacky wrote:
>>> +    /*
>>> +     * native_stop_other_cpus() will write to @stop_cpus_count after
>>> +     * observing that it went down to zero, which will invalidate the
>>> +     * cacheline on this CPU.
>>> +     */
>>> +    atomic_dec(&stop_cpus_count);
> 
> This is probably going to pull in a cache line and cause the problem the
> native_wbinvd() is trying to avoid.

Is one _more_ cacheline really the problem?

Or is having _any_ cacheline pulled in a problem?  What about the text
page containing the WBINVD?  How about all the page table pages that are
needed to resolve %RIP to a physical address?

What about the mds_idle_clear_cpu_buffers() code that snuck into
native_halt()?

> ffffffff810ede4c:       0f 09                   wbinvd 
> ffffffff810ede4e:       8b 05 e4 3b a7 02       mov    0x2a73be4(%rip),%eax        # ffffffff83b61a38 <mds_idle_clear>
> ffffffff810ede54:       85 c0                   test   %eax,%eax
> ffffffff810ede56:       7e 07                   jle    ffffffff810ede5f <stop_this_cpu+0x9f>
> ffffffff810ede58:       0f 00 2d b1 75 13 01    verw   0x11375b1(%rip)        # ffffffff82225410 <ds.6688>
> ffffffff810ede5f:       f4                      hlt    
> ffffffff810ede60:       eb ec                   jmp    ffffffff810ede4e <stop_this_cpu+0x8e>
> ffffffff810ede62:       e8 59 40 1a 00          callq  ffffffff81291ec0 <trace_hardirqs_off>
> ffffffff810ede67:       eb 85                   jmp    ffffffff810eddee <stop_this_cpu+0x2e>
> ffffffff810ede69:       0f 1f 80 00 00 00 00    nopl   0x0(%rax)