6.5-stable review patch. If anyone has any objections, please let me know.
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From: Kirill A. Shutemov kirill.shutemov@linux.intel.com
[ Upstream commit 50e782a86c980d4f8292ef82ed8139282ca07a98 ]
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.
Fixes: 2053bc57f367 ("efi: Add unaccepted memory support") Signed-off-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Reported-by: Michael Roth <michael.roth@amd.com Reviewed-by: Nikolay Borisov nik.borisov@suse.com Reviewed-by: Vlastimil Babka vbabka@suse.cz Tested-by: Michael Roth michael.roth@amd.com [ardb: drop unnecessary cpu_relax() call] Signed-off-by: Ard Biesheuvel ardb@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/firmware/efi/unaccepted_memory.c | 64 ++++++++++++++++++++++-- 1 file changed, 60 insertions(+), 4 deletions(-)
diff --git a/drivers/firmware/efi/unaccepted_memory.c b/drivers/firmware/efi/unaccepted_memory.c index 853f7dc3c21d8..135278ddaf627 100644 --- a/drivers/firmware/efi/unaccepted_memory.c +++ b/drivers/firmware/efi/unaccepted_memory.c @@ -5,9 +5,17 @@ #include <linux/spinlock.h> #include <asm/unaccepted_memory.h>
-/* Protects unaccepted memory bitmap */ +/* Protects unaccepted memory bitmap and accepting_list */ static DEFINE_SPINLOCK(unaccepted_memory_lock);
+struct accept_range { + struct list_head list; + unsigned long start; + unsigned long end; +}; + +static LIST_HEAD(accepting_list); + /* * accept_memory() -- Consult bitmap and accept the memory if needed. * @@ -24,6 +32,7 @@ void accept_memory(phys_addr_t start, phys_addr_t end) { struct efi_unaccepted_memory *unaccepted; unsigned long range_start, range_end; + struct accept_range range, *entry; unsigned long flags; u64 unit_size;
@@ -78,20 +87,67 @@ void accept_memory(phys_addr_t start, phys_addr_t end) if (end > unaccepted->size * unit_size * BITS_PER_BYTE) end = unaccepted->size * unit_size * BITS_PER_BYTE;
- range_start = start / unit_size; - + range.start = start / unit_size; + range.end = DIV_ROUND_UP(end, unit_size); +retry: spin_lock_irqsave(&unaccepted_memory_lock, flags); + + /* + * Check if anybody works on accepting the same range of the memory. + * + * The check is done with unit_size granularity. It is crucial to catch + * all accept requests to the same unit_size block, even if they don't + * overlap on physical address level. + */ + list_for_each_entry(entry, &accepting_list, list) { + if (entry->end < range.start) + continue; + if (entry->start >= range.end) + continue; + + /* + * Somebody else accepting the range. Or at least part of it. + * + * Drop the lock and retry until it is complete. + */ + spin_unlock_irqrestore(&unaccepted_memory_lock, flags); + goto retry; + } + + /* + * Register that the range is about to be accepted. + * Make sure nobody else will accept it. + */ + list_add(&range.list, &accepting_list); + + range_start = range.start; for_each_set_bitrange_from(range_start, range_end, unaccepted->bitmap, - DIV_ROUND_UP(end, unit_size)) { + range.end) { unsigned long phys_start, phys_end; unsigned long len = range_end - range_start;
phys_start = range_start * unit_size + unaccepted->phys_base; phys_end = range_end * unit_size + unaccepted->phys_base;
+ /* + * Keep interrupts disabled until the accept operation is + * complete in order to prevent deadlocks. + * + * Enabling interrupts before calling arch_accept_memory() + * creates an opportunity for an interrupt handler to request + * acceptance for the same memory. The handler will continuously + * spin with interrupts disabled, preventing other task from + * making progress with the acceptance process. + */ + spin_unlock(&unaccepted_memory_lock); + arch_accept_memory(phys_start, phys_end); + + spin_lock(&unaccepted_memory_lock); bitmap_clear(unaccepted->bitmap, range_start, len); } + + list_del(&range.list); spin_unlock_irqrestore(&unaccepted_memory_lock, flags); }