x86/amd-iommu: warn when issuing command to uninitialized cmd buffer

To catch future potential issues we can add a warning whenever we issue
a command before the command buffer is fully initialized.

Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

arch/x86/include/asm/amd_iommu_types.h

@@ -141,6 +141,7 @@
 
 /* constants to configure the command buffer */
 #define CMD_BUFFER_SIZE    8192
+#define CMD_BUFFER_UNINITIALIZED 1
 #define CMD_BUFFER_ENTRIES 512
 #define MMIO_CMD_SIZE_SHIFT 56
 #define MMIO_CMD_SIZE_512 (0x9ULL << MMIO_CMD_SIZE_SHIFT)

arch/x86/kernel/amd_iommu.c

@@ -392,6 +392,7 @@ static int __iommu_queue_command(struct amd_iommu *iommu, struct iommu_cmd *cmd)
 	u32 tail, head;
 	u8 *target;
 
+	WARN_ON(iommu->cmd_buf_size & CMD_BUFFER_UNINITIALIZED);
 	tail = readl(iommu->mmio_base + MMIO_CMD_TAIL_OFFSET);
 	target = iommu->cmd_buf + tail;
 	memcpy_toio(target, cmd, sizeof(*cmd));

arch/x86/kernel/amd_iommu_init.c

@@ -438,7 +438,7 @@ static u8 * __init alloc_command_buffer(struct amd_iommu *iommu)
 	if (cmd_buf == NULL)
 		return NULL;
 
-	iommu->cmd_buf_size = CMD_BUFFER_SIZE;
+	iommu->cmd_buf_size = CMD_BUFFER_SIZE | CMD_BUFFER_UNINITIALIZED;
 
 	return cmd_buf;
 }
@@ -474,12 +474,13 @@ static void iommu_enable_command_buffer(struct amd_iommu *iommu)
 		    &entry, sizeof(entry));
 
 	amd_iommu_reset_cmd_buffer(iommu);
+	iommu->cmd_buf_size &= ~(CMD_BUFFER_UNINITIALIZED);
 }
 
 static void __init free_command_buffer(struct amd_iommu *iommu)
 {
 	free_pages((unsigned long)iommu->cmd_buf,
-		   get_order(iommu->cmd_buf_size));
+		   get_order(iommu->cmd_buf_size & ~(CMD_BUFFER_UNINITIALIZED)));
 }
 
 /* allocates the memory where the IOMMU will log its events to */