linux-kernel - Re: [PATCH] efi/unaccepted: Fix soft lockups caused by parallel memory acceptance

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Date:   Mon, 16 Oct 2023 12:17:49 +0300
From:   Nikolay Borisov <nik.borisov@...e.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Joerg Roedel <jroedel@...e.de>,
        Ard Biesheuvel <ardb@...nel.org>
Cc:     Andi Kleen <ak@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Tom Lendacky <thomas.lendacky@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Dario Faggioli <dfaggioli@...e.com>,
        Mike Rapoport <rppt@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        marcelo.cerri@...onical.com, tim.gardner@...onical.com,
        philip.cox@...onical.com, aarcange@...hat.com, peterx@...hat.com,
        x86@...nel.org, linux-mm@...ck.org, linux-coco@...ts.linux.dev,
        linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...nel.org
Subject: Re: [PATCH] efi/unaccepted: Fix soft lockups caused by parallel
 memory acceptance



On 14.10.23 г. 23:40 ч., Kirill A. Shutemov wrote:
> Michael reported soft lockups on a system that has unaccepted memory.
> This occurs when a user attempts to allocate and accept memory on
> multiple CPUs simultaneously.
> 
> The root cause of the issue is that memory acceptance is serialized with
> a spinlock, allowing only one CPU to accept memory at a time. The other
> CPUs spin and wait for their turn, leading to starvation and soft lockup
> reports.
> 
> To address this, the code has been modified to release the spinlock
> while accepting memory. This allows for parallel memory acceptance on
> multiple CPUs.
> 
> A newly introduced "accepting_list" keeps track of which memory is
> currently being accepted. This is necessary to prevent parallel
> acceptance of the same memory block. If a collision occurs, the lock is
> released and the process is retried.
> 
> Such collisions should rarely occur. The main path for memory acceptance
> is the page allocator, which accepts memory in MAX_ORDER chunks. As long
> as MAX_ORDER is equal to or larger than the unit_size, collisions will
> never occur because the caller fully owns the memory block being
> accepted.
> 
> Aside from the page allocator, only memblock and deferered_free_range()
> accept memory, but this only happens during boot.
> 
> The code has been tested with unit_size == 128MiB to trigger collisions
> and validate the retry codepath.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Reported-by: Michael Roth <michael.roth@....com
> Fixes: 2053bc57f367 ("efi: Add unaccepted memory support")
> Cc: <stable@...nel.org>

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