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Date:   Mon, 16 Oct 2023 12:17:49 +0300
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Subject: Re: [PATCH] efi/unaccepted: Fix soft lockups caused by parallel
 memory acceptance
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To:     "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        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>,
        Ard Biesheuvel <ardb@kernel.org>
Cc:     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
References: <20231014204040.28765-1-kirill.shutemov@linux.intel.com>
From:   Nikolay Borisov <nik.borisov@suse.com>
In-Reply-To: <20231014204040.28765-1-kirill.shutemov@linux.intel.com>
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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@linux.intel.com>
> Reported-by: Michael Roth <michael.roth@amd.com
> Fixes: 2053bc57f367 ("efi: Add unaccepted memory support")
> Cc: <stable@kernel.org>

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