[v1,1/4] memory: allocation in low memory

Commit Message

Pierre Morel Sept. 25, 2020, 4:02 p.m. UTC

Some architectures need allocations to be done under a
specific address limit to allow DMA from I/O.

We propose here a very simple page allocator to get
pages allocated under this specific limit.

The DMA page allocator will only use part of the available memory
under the DMA address limit to let room for the standard allocator.

Signed-off-by: Pierre Morel <[e-mail]>
---
 lib/alloc_dma_page.c | 57 ++++++++++++++++++++++++++++++++++++++++++++
 lib/alloc_dma_page.h | 24 +++++++++++++++++++
 lib/s390x/sclp.c     |  2 ++
 s390x/Makefile       |  1 +
 4 files changed, 84 insertions(+)
 create mode 100644 lib/alloc_dma_page.c
 create mode 100644 lib/alloc_dma_page.h

Comments

Pierre Morel Sept. 25, 2020, 4:08 p.m. UTC | #1

Arrrghh sorry, I forgot the kvm-unit-tests TAG


On 2020-09-25 18:02, Pierre Morel wrote:
> Some architectures need allocations to be done under a
> specific address limit to allow DMA from I/O.
> 
> We propose here a very simple page allocator to get
> pages allocated under this specific limit.
> 
> The DMA page allocator will only use part of the available memory
> under the DMA address limit to let room for the standard allocator.
>

Patch

diff --git a/lib/alloc_dma_page.c b/lib/alloc_dma_page.c
new file mode 100644
index 0000000..6a16e38
--- /dev/null
+++ b/lib/alloc_dma_page.c
@@ -0,0 +1,57 @@ 
+/*
+ * Page allocator for DMA
+ *
+ * Copyright (c) IBM, Corp. 2020
+ *
+ * Authors:
+ *  Pierre Morel <[e-mail]>
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU Library General Public License version 2.
+ */
+#include <libcflat.h>
+#include <asm/spinlock.h>
+#include <alloc_dma_page.h>
+
+static struct spinlock lock;
+static void *dma_freelist = 0;
+
+void put_dma_page(void *dma_page)
+{
+	spin_lock(&lock);
+	*(void **)dma_page = dma_freelist;
+	dma_freelist = dma_page;
+	spin_unlock(&lock);
+}
+
+void *get_dma_page(void)
+{
+	void *p = NULL;
+
+	spin_lock(&lock);
+	if (!dma_freelist)
+		goto end_unlock;
+
+	p = dma_freelist;
+	dma_freelist = *(void **)dma_freelist;
+
+end_unlock:
+	spin_unlock(&lock);
+	return p;
+}
+
+phys_addr_t dma_page_alloc_init(phys_addr_t start, phys_addr_t end)
+{
+	int start_pfn = start >> PAGE_SHIFT;
+	int nb_pfn = ((end - start) >> PAGE_SHIFT) - 1;
+	int max, pfn;
+
+	max = start_pfn + nb_pfn / DMA_ALLOC_RATIO;
+	if (max > DMA_MAX_PFN)
+		max = DMA_MAX_PFN;
+
+	for (pfn = start_pfn; pfn < max; pfn++)
+		put_dma_page((void *)((unsigned long) pfn << PAGE_SHIFT));
+
+	return (phys_addr_t)pfn << PAGE_SHIFT;
+}
diff --git a/lib/alloc_dma_page.h b/lib/alloc_dma_page.h
new file mode 100644
index 0000000..85e1d2f
--- /dev/null
+++ b/lib/alloc_dma_page.h
@@ -0,0 +1,24 @@ 
+/*
+ * Page allocator for DMA definitions
+ *
+ * Copyright (c) IBM, Corp. 2020
+ *
+ * Authors:
+ *  Pierre Morel <[e-mail]>
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU Library General Public License version 2.
+ */
+#ifndef _ALLOC_DMA_PAGE_H_
+#define _ALLOC_DMA_PAGE_H_
+
+#include <asm/page.h>
+
+void put_dma_page(void *dma_page);
+void *get_dma_page(void);
+phys_addr_t dma_page_alloc_init(phys_addr_t start_pfn, phys_addr_t nb_pages);
+
+#define DMA_MAX_PFN	(0x80000000 >> PAGE_SHIFT)
+#define DMA_ALLOC_RATIO	8
+
+#endif /* _ALLOC_DMA_PAGE_H_ */
diff --git a/lib/s390x/sclp.c b/lib/s390x/sclp.c
index 4054d0e..9c95ca5 100644
--- a/lib/s390x/sclp.c
+++ b/lib/s390x/sclp.c
@@ -19,6 +19,7 @@ 
 #include "sclp.h"
 #include <alloc_phys.h>
 #include <alloc_page.h>
+#include <alloc_dma_page.h>
 
 extern unsigned long stacktop;
 
@@ -35,6 +36,7 @@  static void mem_init(phys_addr_t mem_end)
 	phys_addr_t freemem_start = (phys_addr_t)&stacktop;
 	phys_addr_t base, top;
 
+	freemem_start = dma_page_alloc_init(freemem_start, mem_end);
 	phys_alloc_init(freemem_start, mem_end - freemem_start);
 	phys_alloc_get_unused(&base, &top);
 	base = (base + PAGE_SIZE - 1) & -PAGE_SIZE;
diff --git a/s390x/Makefile b/s390x/Makefile
index 9144d57..109ef9f 100644
--- a/s390x/Makefile
+++ b/s390x/Makefile
@@ -52,6 +52,7 @@  cflatobjs += lib/alloc_phys.o
 cflatobjs += lib/alloc_page.o
 cflatobjs += lib/vmalloc.o
 cflatobjs += lib/alloc_phys.o
+cflatobjs += lib/alloc_dma_page.o
 cflatobjs += lib/s390x/io.o
 cflatobjs += lib/s390x/stack.o
 cflatobjs += lib/s390x/sclp.o