Re: [PATCHv14 5/9] efi: Add unaccepted memory support

["Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>]

On Fri, Oct 13, 2023 at 08:27:28PM +0300, Kirill A. Shutemov wrote:
> I will test the idea with larger unit_size to see how it behaves.

It indeed uncovered an issue. We need to record ranges on accepting_list
in unit_size granularity. Otherwise, we fail to stop parallel accept
requests to the same unit_size block if they don't overlap on physical
addresses.

Updated patch:

diff --git a/drivers/firmware/efi/unaccepted_memory.c b/drivers/firmware/efi/unaccepted_memory.c
index 853f7dc3c21d..8af0306c8e5c 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 +87,58 @@ 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 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);
+		cond_resched();
+		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;
 
+		spin_unlock_irqrestore(&unaccepted_memory_lock, flags);
+
 		arch_accept_memory(phys_start, phys_end);
+
+		spin_lock_irqsave(&unaccepted_memory_lock, flags);
 		bitmap_clear(unaccepted->bitmap, range_start, len);
 	}
+
+	list_del(&range.list);
 	spin_unlock_irqrestore(&unaccepted_memory_lock, flags);
 }
 
-- 
  Kiryl Shutsemau / Kirill A. Shutemov