linux-kernel - Re: [RFC PATCH] mm, oom: distinguish blockable mode for mmu notifiers

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Date:   Mon, 25 Jun 2018 10:45:29 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm@...r.kernel.org,
        Radim Krčmář <rkrcmar@...hat.com>,
        linux-mm@...ck.org, Andrea Arcangeli <aarcange@...hat.com>,
        Jérôme Glisse <jglisse@...hat.com>
Subject: Re: [RFC PATCH] mm, oom: distinguish blockable mode for mmu notifiers

On Mon 25-06-18 10:10:18, Paolo Bonzini wrote:
> On 25/06/2018 09:57, Michal Hocko wrote:
> > On Sun 24-06-18 10:11:21, Paolo Bonzini wrote:
> >> On 22/06/2018 17:02, Michal Hocko wrote:
> >>> @@ -7215,6 +7216,8 @@ void kvm_arch_mmu_notifier_invalidate_range(struct kvm *kvm,
> >>>  	apic_address = gfn_to_hva(kvm, APIC_DEFAULT_PHYS_BASE >> PAGE_SHIFT);
> >>>  	if (start <= apic_address && apic_address < end)
> >>>  		kvm_make_all_cpus_request(kvm, KVM_REQ_APIC_PAGE_RELOAD);
> >>> +
> >>> +	return 0;
> >>
> >> This is wrong, gfn_to_hva can sleep.
> > 
> > Hmm, I have tried to crawl the call chain and haven't found any
> > sleepable locks taken. Maybe I am just missing something.
> > __kvm_memslots has a complex locking assert. I do not see we would take
> > slots_lock anywhere from the notifier call path. IIUC that means that
> > users_count has to be zero at that time. I have no idea how that is
> > guaranteed.
> 
> Nevermind, ENOCOFFEE.  This is gfn_to_hva, not gfn_to_pfn.  It only
> needs SRCU.

OK, so just the make sure I follow, the change above is correct?
-- 
Michal Hocko
SUSE Labs