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Date:   Tue, 17 Oct 2023 12:44:03 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
To:     Ard Biesheuvel <ardb@kernel.org>
Cc:     Matthew Wilcox <willy@infradead.org>,
        Borislav Petkov <bp@alien8.de>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Sean Christopherson <seanjc@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Joerg Roedel <jroedel@suse.de>,
        Andi Kleen <ak@linux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        David Rientjes <rientjes@google.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Ingo Molnar <mingo@redhat.com>,
        Dario Faggioli <dfaggioli@suse.com>,
        Mike Rapoport <rppt@kernel.org>,
        David Hildenbrand <david@redhat.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        marcelo.cerri@canonical.com, tim.gardner@canonical.com,
        philip.cox@canonical.com, aarcange@redhat.com, peterx@redhat.com,
        x86@kernel.org, linux-mm@kvack.org, linux-coco@lists.linux.dev,
        linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org,
        stable@kernel.org, Nikolay Borisov <nik.borisov@suse.com>
Subject: Re: [PATCHv2] efi/unaccepted: Fix soft lockups caused by parallel
 memory acceptance
Message-ID: <20231017094403.g6laxp2c3vwzt2sw@box.shutemov.name>
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On Tue, Oct 17, 2023 at 09:42:13AM +0200, Ard Biesheuvel wrote:
> On Mon, 16 Oct 2023 at 23:39, Kirill A. Shutemov
> <kirill.shutemov@linux.intel.com> wrote:
> >
> > On Mon, Oct 16, 2023 at 06:55:41PM +0100, Matthew Wilcox wrote:
> > > On Mon, Oct 16, 2023 at 07:31:22PM +0300, Kirill A. Shutemov wrote:
> > > >   v2:
> > > >    - Fix deadlock (Vlastimil);
> > > >    - Fix comments (Vlastimil);
> > > >    - s/cond_resched()/cpu_relax()/ -- cond_resched() cannot be called
> > > >      from atomic context;
> > >
> > > Isn't there an implicit cpu_relax() while we're spinning?  Does this
> > > really accomplish anything?
> >
> > You are right. It is useless. I will drop it in v3.
> >
> 
> I can drop that bit when applying the patch.
> 
> One question I have is whether the sequence
> 
> spin_lock_irqsave(&unaccepted_memory_lock, flags);
> ...
> spin_unlock(&unaccepted_memory_lock);
> arch_accept_memory(phys_start, phys_end);
> spin_lock(&unaccepted_memory_lock);
> ...
> spin_unlock_irqrestore(&unaccepted_memory_lock, flags);
> 
> is considered sound and is supported by all architectures?

I am not an locking expert and only tested it on x86. But what potential
issue do you see?

-- 
  Kiryl Shutsemau / Kirill A. Shutemov