Re: [PATCH 2/8] xen/balloon: Move common memory reservation routines to a module

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On 05/29/2018 09:04 PM, Boris Ostrovsky wrote:
On 05/25/2018 11:33 AM, Oleksandr Andrushchenko wrote:
From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>

Memory {increase|decrease}_reservation and VA mappings update/reset
code used in balloon driver can be made common, so other drivers can
also re-use the same functionality without open-coding.
Create a dedicated module
IIUIC this is not really a module, it's a common file.
Sure, will put "file" here

for the shared code and export corresponding
symbols for other kernel modules.

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
---
  drivers/xen/Makefile          |   1 +
  drivers/xen/balloon.c         |  71 ++----------------
  drivers/xen/mem-reservation.c | 134 ++++++++++++++++++++++++++++++++++
  include/xen/mem_reservation.h |  29 ++++++++
  4 files changed, 170 insertions(+), 65 deletions(-)
  create mode 100644 drivers/xen/mem-reservation.c
  create mode 100644 include/xen/mem_reservation.h

diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
index 451e833f5931..3c87b0c3aca6 100644
--- a/drivers/xen/Makefile
+++ b/drivers/xen/Makefile
@@ -2,6 +2,7 @@
  obj-$(CONFIG_HOTPLUG_CPU)		+= cpu_hotplug.o
  obj-$(CONFIG_X86)			+= fallback.o
  obj-y	+= grant-table.o features.o balloon.o manage.o preempt.o time.o
+obj-y	+= mem-reservation.o
  obj-y	+= events/
  obj-y	+= xenbus/
diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index 065f0b607373..57b482d67a3a 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -71,6 +71,7 @@
  #include <xen/balloon.h>
  #include <xen/features.h>
  #include <xen/page.h>
+#include <xen/mem_reservation.h>
static int xen_hotplug_unpopulated; @@ -157,13 +158,6 @@ static DECLARE_DELAYED_WORK(balloon_worker, balloon_process);
  #define GFP_BALLOON \
  	(GFP_HIGHUSER | __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC)
-static void scrub_page(struct page *page)
-{
-#ifdef CONFIG_XEN_SCRUB_PAGES
-	clear_highpage(page);
-#endif
-}
-
  /* balloon_append: add the given page to the balloon. */
  static void __balloon_append(struct page *page)
  {
@@ -463,11 +457,6 @@ static enum bp_state increase_reservation(unsigned long nr_pages)
  	int rc;
  	unsigned long i;
  	struct page   *page;
-	struct xen_memory_reservation reservation = {
-		.address_bits = 0,
-		.extent_order = EXTENT_ORDER,
-		.domid        = DOMID_SELF
-	};
if (nr_pages > ARRAY_SIZE(frame_list))
  		nr_pages = ARRAY_SIZE(frame_list);
@@ -486,9 +475,7 @@ static enum bp_state increase_reservation(unsigned long nr_pages)
  		page = balloon_next_page(page);
  	}
- set_xen_guest_handle(reservation.extent_start, frame_list);
-	reservation.nr_extents = nr_pages;
-	rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);
+	rc = xenmem_reservation_increase(nr_pages, frame_list);
  	if (rc <= 0)
  		return BP_EAGAIN;
@@ -496,29 +483,7 @@ static enum bp_state increase_reservation(unsigned long nr_pages)
  		page = balloon_retrieve(false);
  		BUG_ON(page == NULL);
-#ifdef CONFIG_XEN_HAVE_PVMMU
-		/*
-		 * We don't support PV MMU when Linux and Xen is using
-		 * different page granularity.
-		 */
-		BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
-
-		if (!xen_feature(XENFEAT_auto_translated_physmap)) {
-			unsigned long pfn = page_to_pfn(page);
-
-			set_phys_to_machine(pfn, frame_list[i]);
-
-			/* Link back into the page tables if not highmem. */
-			if (!PageHighMem(page)) {
-				int ret;
-				ret = HYPERVISOR_update_va_mapping(
-						(unsigned long)__va(pfn << PAGE_SHIFT),
-						mfn_pte(frame_list[i], PAGE_KERNEL),
-						0);
-				BUG_ON(ret);
-			}
-		}
-#endif
+		xenmem_reservation_va_mapping_update(1, &page, &frame_list[i]);

Can you make a single call to xenmem_reservation_va_mapping_update(rc,
...)? You need to keep track of pages but presumable they can be put
into an array (or a list). In fact, perhaps we can have
balloon_retrieve() return a set of pages.
This is actually how it is used later on for dma-buf, but I just didn't want
to alter original balloon code too much, but this can be done, in order of simplicity:

1. Similar to frame_list, e.g. static array of struct page* of size ARRAY_SIZE(frame_list):
more static memory is used, but no allocations

2. Allocated at run-time with kcalloc: allocation can fail

3. Make balloon_retrieve() return a set of pages: will require list/array allocation
and handling, allocation may fail, balloon_retrieve prototype change

Could you please tell which of the above will fit better?




/* Relinquish the page back to the allocator. */
  		free_reserved_page(page);
@@ -535,11 +500,6 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
  	unsigned long i;
  	struct page *page, *tmp;
  	int ret;
-	struct xen_memory_reservation reservation = {
-		.address_bits = 0,
-		.extent_order = EXTENT_ORDER,
-		.domid        = DOMID_SELF
-	};
  	LIST_HEAD(pages);
if (nr_pages > ARRAY_SIZE(frame_list))
@@ -553,7 +513,7 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
  			break;
  		}
  		adjust_managed_page_count(page, -1);
-		scrub_page(page);
+		xenmem_reservation_scrub_page(page);
  		list_add(&page->lru, &pages);
  	}
@@ -575,25 +535,8 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
  		/* XENMEM_decrease_reservation requires a GFN */
  		frame_list[i++] = xen_page_to_gfn(page);
-#ifdef CONFIG_XEN_HAVE_PVMMU
-		/*
-		 * We don't support PV MMU when Linux and Xen is using
-		 * different page granularity.
-		 */
-		BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
-
-		if (!xen_feature(XENFEAT_auto_translated_physmap)) {
-			unsigned long pfn = page_to_pfn(page);
+		xenmem_reservation_va_mapping_reset(1, &page);

and here too.
see above

- if (!PageHighMem(page)) {
-				ret = HYPERVISOR_update_va_mapping(
-						(unsigned long)__va(pfn << PAGE_SHIFT),
-						__pte_ma(0), 0);
-				BUG_ON(ret);
-			}
-			__set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
-		}
-#endif
  		list_del(&page->lru);
balloon_append(page);
@@ -601,9 +544,7 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
flush_tlb_all(); - set_xen_guest_handle(reservation.extent_start, frame_list);
-	reservation.nr_extents   = nr_pages;
-	ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation);
+	ret = xenmem_reservation_decrease(nr_pages, frame_list);
  	BUG_ON(ret != nr_pages);
balloon_stats.current_pages -= nr_pages;
diff --git a/drivers/xen/mem-reservation.c b/drivers/xen/mem-reservation.c
new file mode 100644
index 000000000000..29882e4324f5
--- /dev/null
+++ b/drivers/xen/mem-reservation.c
@@ -0,0 +1,134 @@
+// SPDX-License-Identifier: GPL-2.0 OR MIT

Why is this "OR MIT"? The original file was licensed GPLv2 only.
Will fix - I was not sure about the license to be used here, thanks

+
+/******************************************************************************
+ * Xen memory reservation utilities.
+ *
+ * Copyright (c) 2003, B Dragovic
+ * Copyright (c) 2003-2004, M Williamson, K Fraser
+ * Copyright (c) 2005 Dan M. Smith, IBM Corporation
+ * Copyright (c) 2010 Daniel Kiper
+ * Copyright (c) 2018, Oleksandr Andrushchenko, EPAM Systems Inc.
+ */
+
+#include <linux/kernel.h>
+#include <linux/slab.h>
+
+#include <asm/tlb.h>
+#include <asm/xen/hypercall.h>
+
+#include <xen/interface/memory.h>
+#include <xen/page.h>
+
+/*
+ * Use one extent per PAGE_SIZE to avoid to break down the page into
+ * multiple frame.
+ */
+#define EXTENT_ORDER (fls(XEN_PFN_PER_PAGE) - 1)
+
+void xenmem_reservation_scrub_page(struct page *page)
+{
+#ifdef CONFIG_XEN_SCRUB_PAGES
+	clear_highpage(page);
+#endif
+}
+EXPORT_SYMBOL(xenmem_reservation_scrub_page);
+
+void xenmem_reservation_va_mapping_update(unsigned long count,
+					  struct page **pages,
+					  xen_pfn_t *frames)
+{
+#ifdef CONFIG_XEN_HAVE_PVMMU
+	int i;
+
+	for (i = 0; i < count; i++) {
+		struct page *page;
+
+		page = pages[i];
+		BUG_ON(page == NULL);
+
+		/*
+		 * We don't support PV MMU when Linux and Xen is using
+		 * different page granularity.
+		 */
+		BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
+
+		if (!xen_feature(XENFEAT_auto_translated_physmap)) {
+			unsigned long pfn = page_to_pfn(page);
+
+			set_phys_to_machine(pfn, frames[i]);
+
+			/* Link back into the page tables if not highmem. */
+			if (!PageHighMem(page)) {
+				int ret;
+
+				ret = HYPERVISOR_update_va_mapping(
+						(unsigned long)__va(pfn << PAGE_SHIFT),
+						mfn_pte(frames[i], PAGE_KERNEL),
+						0);
+				BUG_ON(ret);
+			}
+		}
+	}
+#endif
+}
+EXPORT_SYMBOL(xenmem_reservation_va_mapping_update);
+
+void xenmem_reservation_va_mapping_reset(unsigned long count,
+					 struct page **pages)
+{
+#ifdef CONFIG_XEN_HAVE_PVMMU
+	int i;
+
+	for (i = 0; i < count; i++) {
+		/*
+		 * We don't support PV MMU when Linux and Xen is using
+		 * different page granularity.
+		 */
+		BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
+
+		if (!xen_feature(XENFEAT_auto_translated_physmap)) {
+			struct page *page = pages[i];
+			unsigned long pfn = page_to_pfn(page);
+
+			if (!PageHighMem(page)) {
+				int ret;
+
+				ret = HYPERVISOR_update_va_mapping(
+						(unsigned long)__va(pfn << PAGE_SHIFT),
+						__pte_ma(0), 0);
+				BUG_ON(ret);
+			}
+			__set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
+		}
+	}
+#endif
+}
+EXPORT_SYMBOL(xenmem_reservation_va_mapping_reset);
+
+int xenmem_reservation_increase(int count, xen_pfn_t *frames)
+{
+	struct xen_memory_reservation reservation = {
+		.address_bits = 0,
+		.extent_order = EXTENT_ORDER,
+		.domid        = DOMID_SELF
+	};
+
+	set_xen_guest_handle(reservation.extent_start, frames);
+	reservation.nr_extents = count;
+	return HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);
+}
+EXPORT_SYMBOL(xenmem_reservation_increase);
+
+int xenmem_reservation_decrease(int count, xen_pfn_t *frames)
+{
+	struct xen_memory_reservation reservation = {
+		.address_bits = 0,
+		.extent_order = EXTENT_ORDER,
+		.domid        = DOMID_SELF
+	};
+
+	set_xen_guest_handle(reservation.extent_start, frames);
+	reservation.nr_extents = count;
+	return HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation);
+}
+EXPORT_SYMBOL(xenmem_reservation_decrease);
diff --git a/include/xen/mem_reservation.h b/include/xen/mem_reservation.h
new file mode 100644
index 000000000000..9306d9b8743c
--- /dev/null
+++ b/include/xen/mem_reservation.h
@@ -0,0 +1,29 @@
+/* SPDX-License-Identifier: GPL-2.0 OR MIT */
and here too.
will fix

-boris

Thank you,
Oleksandr
+
+/*
+ * Xen memory reservation utilities.
+ *
+ * Copyright (c) 2003, B Dragovic
+ * Copyright (c) 2003-2004, M Williamson, K Fraser
+ * Copyright (c) 2005 Dan M. Smith, IBM Corporation
+ * Copyright (c) 2010 Daniel Kiper
+ * Copyright (c) 2018, Oleksandr Andrushchenko, EPAM Systems Inc.
+ */
+
+#ifndef _XENMEM_RESERVATION_H
+#define _XENMEM_RESERVATION_H
+
+void xenmem_reservation_scrub_page(struct page *page);
+
+void xenmem_reservation_va_mapping_update(unsigned long count,
+					  struct page **pages,
+					  xen_pfn_t *frames);
+
+void xenmem_reservation_va_mapping_reset(unsigned long count,
+					 struct page **pages);
+
+int xenmem_reservation_increase(int count, xen_pfn_t *frames);
+
+int xenmem_reservation_decrease(int count, xen_pfn_t *frames);
+
+#endif




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