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

[Oleksandr Andrushchenko <andr2000@gmail.com>]

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@epam.com>
>>
>> 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@epam.com>
>> ---
>>   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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