Re: [PATCHv11 18/19] x86/acpi: Add support for CPU offlining for ACPI MADT wakeup method

[Kirill A. Shutemov]

On Mon, Jun 10, 2024 at 03:40:20PM +0200, Borislav Petkov wrote:
> On Fri, Jun 07, 2024 at 06:14:28PM +0300, Kirill A. Shutemov wrote:
> >   I was able to address this issue by switching cpa_lock to a mutex.
> >   However, this solution will only work if the callers for set_memory
> >   interfaces are not called from an atomic context. I need to verify if
> >   this is the case.
> 
> Dunno, I'd be nervous about this. Althouth from looking at
> 
>    ad5ca55f6bdb ("x86, cpa: srlz cpa(), global flush tlb after splitting big page and before doing cpa")
> 
> I don't see how "So that we don't allow any other cpu" can't be done
> with a mutex. Perhaps the set_memory* interfaces should be usable in as
> many contexts as possible.
> 
> Have you run this with lockdep enabled?

Yes, it booted to the shell just fine. However, that doesn't prove
anything. The set_memory_* function has many obscured cases.

> > - The function __flush_tlb_all() in kernel_(un)map_pages_in_pgd() must be
> >   called with preemption disabled. Once again, I am unsure why this has
> >   not caused issues in the EFI case.
> 
> It could be because EFI does all that setup on the BSP only before the
> others have arrived but I don't remember anymore... It is more than
> a decade ago when I did this...

Are you okay with this? Disabling preemption looks strange, but I don't
see a better option.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov