linux-kernel - Re: [PATCH] efi/unaccepted: touch soft lockup during memory accept

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Date: Thu, 11 Apr 2024 08:36:37 +0800
From: Chen Yu <yu.c.chen@...el.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
CC: <linux-efi@...r.kernel.org>, Ard Biesheuvel <ardb@...nel.org>, Chao Gao
	<chao.gao@...el.com>, <linux-kernel@...r.kernel.org>, "Hossain, Md Iqbal"
	<md.iqbal.hossain@...el.com>
Subject: Re: [PATCH] efi/unaccepted: touch soft lockup during memory accept

On 2024-04-10 at 15:35:39 +0300, Kirill A. Shutemov wrote:
> On Wed, Apr 10, 2024 at 06:23:01PM +0800, Chen Yu wrote:
> > Commit 50e782a86c98 ("efi/unaccepted: Fix soft lockups caused
> > by parallel memory acceptance") has released the spinlock so
> > other CPUs can do memory acceptance in parallel and not
> > triggers softlockup on other CPUs.
> > 
> > However the softlock up was intermittent shown up if the memory
> > of the TD guest is large, and the timeout of softlockup is set
> > to 1 second:
> > 
> >  RIP: 0010:_raw_spin_unlock_irqrestore
> >  Call Trace:
> >  ? __hrtimer_run_queues
> >  <IRQ>
> >  ? hrtimer_interrupt
> >  ? watchdog_timer_fn
> >  ? __sysvec_apic_timer_interrupt
> >  ? __pfx_watchdog_timer_fn
> >  ? sysvec_apic_timer_interrupt
> >  </IRQ>
> >  ? __hrtimer_run_queues
> >  <TASK>
> >  ? hrtimer_interrupt
> >  ? asm_sysvec_apic_timer_interrupt
> >  ? _raw_spin_unlock_irqrestore
> >  ? __sysvec_apic_timer_interrupt
> >  ? sysvec_apic_timer_interrupt
> >  accept_memory
> >  try_to_accept_memory
> >  do_huge_pmd_anonymous_page
> >  get_page_from_freelist
> >  __handle_mm_fault
> >  __alloc_pages
> >  __folio_alloc
> >  ? __tdx_hypercall
> >  handle_mm_fault
> >  vma_alloc_folio
> >  do_user_addr_fault
> >  do_huge_pmd_anonymous_page
> >  exc_page_fault
> >  ? __do_huge_pmd_anonymous_page
> >  asm_exc_page_fault
> >  __handle_mm_fault
> 
> Stacktrace doesn't add much value here. Just drop it.
>

OK, will do.
 
> > When the local irq is enabled at the end of accept_memory(),
> > the softlockup detects that the watchdog on single CPU has
> > not been fed for a while. That is to say, even other CPUs
> > will not be blocked by spinlock, the current CPU might be
> > stunk with local irq disabled for a while, which hurts not
> > only nmi watchdog but also softlockup.
> > 
> > Chao Gao pointed out that the memory accept could be time
> > costly and there was similar report before. Thus to avoid
> > any softlocup detection during this stage, give the
> > softlockup a flag to skip the timeout check at the end of
> > accept_memory(), by invoking touch_softlockup_watchdog().
> > 
> > Reported-by: "Hossain, Md Iqbal" <md.iqbal.hossain@...el.com>
> > Signed-off-by: Chen Yu <yu.c.chen@...el.com>
> 
> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> 
> And I think it is justified to add Fixes tag:
> 
> Fixes: 50e782a86c98 ("efi/unaccepted: Fix soft lockups caused by parallel memory acceptance")
>

OK, I'll refine the patch and send v2, thanks!


thanks,Chenyu