Re: [PATCH v2] x86/virt/tdx: Fix lockdep assertion failure in cache flush for kexec

[Nikolay Borisov]

On 5.03.26 г. 23:35 ч., Huang, Kai wrote:
> > > The real requirement is tdx_cpu_flush_cache_for_kexec() must be done on
> > > the same CPU.  It's OK that it can be preempted in the middle as long as
> > > it won't be rescheduled to another CPU.
> >
> > TLDR: It wants migration disabled.
>
> Basically yes.
>
> > > Remove the too strong lockdep_assert_preemption_disabled(), and change
> > > this_cpu_{read|write}() to __this_cpu_{read|write}() which provide the more
> > > proper check (when CONFIG_DEBUG_PREEMPT is true), which checks all
> > > conditions that the context cannot be moved to another CPU to run in the
> > > middle.
> > >
> > > Fixes: 61221d07e815 ("KVM/TDX: Explicitly do WBINVD when no more TDX SEAMCALLs")
> > > Cc: stable@xxxxxxxxxxxxxxx
> > > Reported-by: Vishal Verma <vishal.l.verma@xxxxxxxxx>
> > > Signed-off-by: Kai Huang <kai.huang@xxxxxxxxx>
> > > Tested-by: Vishal Verma <vishal.l.verma@xxxxxxxxx>
> >
> >
> > So how exactly does this patch prevent the BUG: printk in
> > check_preemption_disabled from triggering, if the lockdep assert was
> > triggering?
>
> There's no real BUG here.  It's just the
> lockdep_assert_preemption_disabled() is misused.

Essentially in check_preemption_disabled() the check is considered 
passed IF ANY of the preempt disable conditions is met, i.e it's more 
laxed. So yeah, makes sense!

Reviewed-by: Nikolay Borisov <nik.borisov@xxxxxxxx>