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Shutemov" , Borislav Petkov , Andy Lutomirski , Dave Hansen , Sean Christopherson , Andrew Morton , Joerg Roedel , Ard Biesheuvel Cc: Andi Kleen , Kuppuswamy Sathyanarayanan , David Rientjes , Vlastimil Babka , Tom Lendacky , Thomas Gleixner , Peter Zijlstra , Paolo Bonzini , Ingo Molnar , Dario Faggioli , Mike Rapoport , David Hildenbrand , Mel Gorman , 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 In-Reply-To: <20231014204040.28765-1-kirill.shutemov@linux.intel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: FR2P281CA0086.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:9b::14) To PA4PR04MB7790.eurprd04.prod.outlook.com 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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 > Reported-by: Michael Roth Fixes: 2053bc57f367 ("efi: Add unaccepted memory support") > Cc: Reviewed-by: Nikolay Borisov