[PATCH 1/2] kexec: remove unnecessary unusable_pages

[PATCH 1/2] kexec: remove unnecessary unusable_pages

[zhongjiang]

From: zhong jiang <zhongjiang@huawei.com>

In general, kexec alloc pages from buddy system, it cannot exceed
the physical address in the system.

The patch just remove this code, no functional change.

Signed-off-by: zhong jiang <zhongjiang@huawei.com>
---
 include/linux/kexec.h |  1 -
 kernel/kexec_core.c   | 13 -------------
 2 files changed, 14 deletions(-)

diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index e8acb2b..26e4917 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -162,7 +162,6 @@ struct kimage {
 
 	struct list_head control_pages;
 	struct list_head dest_pages;
-	struct list_head unusable_pages;
 
 	/* Address of next control page to allocate for crash kernels. */
 	unsigned long control_page;
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index 56b3ed0..448127d 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -257,9 +257,6 @@ struct kimage *do_kimage_alloc_init(void)
 	/* Initialize the list of destination pages */
 	INIT_LIST_HEAD(&image->dest_pages);
 
-	/* Initialize the list of unusable pages */
-	INIT_LIST_HEAD(&image->unusable_pages);
-
 	return image;
 }
 
@@ -517,10 +514,6 @@ static void kimage_free_extra_pages(struct kimage *image)
 {
 	/* Walk through and free any extra destination pages I may have */
 	kimage_free_page_list(&image->dest_pages);
-
-	/* Walk through and free any unusable pages I have cached */
-	kimage_free_page_list(&image->unusable_pages);
-
 }
 void kimage_terminate(struct kimage *image)
 {
@@ -647,12 +640,6 @@ static struct page *kimage_alloc_page(struct kimage *image,
 		page = kimage_alloc_pages(gfp_mask, 0);
 		if (!page)
 			return NULL;
-		/* If the page cannot be used file it away */
-		if (page_to_pfn(page) >
-				(KEXEC_SOURCE_MEMORY_LIMIT >> PAGE_SHIFT)) {
-			list_add(&page->lru, &image->unusable_pages);
-			continue;
-		}
 		addr = page_to_pfn(page) << PAGE_SHIFT;
 
 		/* If it is the destination page we want use it */
-- 
1.8.3.1

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[PATCH 2/2] kexec: add a pmd huge entry condition during the page table

[zhongjiang]

From: zhong jiang <zhongjiang@huawei.com>

when image is loaded into kernel, we need set up page table for it.
and all valid pfn also set up new mapping. it will set up a pmd huge
entry if pud_present is true.  relocate_kernel points to code segment
can locate in the pmd huge entry in init_transtion_pgtable. therefore,
we need to take the situation into account.

Signed-off-by: zhong jiang <zhongjiang@huawei.com>
---
 arch/x86/kernel/machine_kexec_64.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
index 5a294e4..c33e344 100644
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -14,6 +14,7 @@
 #include <linux/gfp.h>
 #include <linux/reboot.h>
 #include <linux/numa.h>
+#include <linux/hugetlb.h>
 #include <linux/ftrace.h>
 #include <linux/io.h>
 #include <linux/suspend.h>
@@ -34,6 +35,17 @@ static struct kexec_file_ops *kexec_file_loaders[] = {
 };
 #endif
 
+static void split_pmd(pmd_t *pmd, pte_t *pte)
+{
+	unsigned long pfn = pmd_pfn(*pmd);
+	int i = 0;
+
+	do {
+		set_pte(pte, pfn_pte(pfn, PAGE_KERNEL_EXEC));
+		pfn++;
+	} while (pte++, i++, i < PTRS_PER_PTE);
+}
+
 static void free_transition_pgtable(struct kimage *image)
 {
 	free_page((unsigned long)image->arch.pud);
@@ -68,15 +80,19 @@ static int init_transition_pgtable(struct kimage *image, pgd_t *pgd)
 		set_pud(pud, __pud(__pa(pmd) | _KERNPG_TABLE));
 	}
 	pmd = pmd_offset(pud, vaddr);
-	if (!pmd_present(*pmd)) {
+	if (!pmd_present(*pmd) || pmd_huge(*pmd)) {
 		pte = (pte_t *)get_zeroed_page(GFP_KERNEL);
 		if (!pte)
 			goto err;
 		image->arch.pte = pte;
-		set_pmd(pmd, __pmd(__pa(pte) | _KERNPG_TABLE));
+		if (pmd_huge(*pmd))
+			split_pmd(pmd, pte);
+		else
+			set_pmd(pmd, __pmd(__pa(pte) | _KERNPG_TABLE));
 	}
 	pte = pte_offset_kernel(pmd, vaddr);
 	set_pte(pte, pfn_pte(paddr >> PAGE_SHIFT, PAGE_KERNEL_EXEC));
+
 	return 0;
 err:
 	free_transition_pgtable(image);
-- 
1.8.3.1

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Re: [PATCH 2/2] kexec: add a pmd huge entry condition during the page table

[Andrew Morton]

On Mon, 11 Jul 2016 14:36:01 +0800 zhongjiang <zhongjiang@huawei.com> wrote:

> From: zhong jiang <zhongjiang@huawei.com>
> 
> when image is loaded into kernel, we need set up page table for it.
> and all valid pfn also set up new mapping. it will set up a pmd huge
> entry if pud_present is true.  relocate_kernel points to code segment
> can locate in the pmd huge entry in init_transtion_pgtable. therefore,
> we need to take the situation into account.

Sorry, I just don't understand this changelog.  The second sentence is
particularly hard.

So can you please have another attempt at preparing the changelog text?
The resend the patches and this time be sure to Cc the kexec
maintainers.  I suggest this list:

Cc: kexec@lists.infradead.org
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Simon Horman <horms@verge.net.au>

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Re: [PATCH 2/2] kexec: add a pmd huge entry condition during the page table

[zhong jiang]

On 2016/7/12 4:25, Andrew Morton wrote:
> On Mon, 11 Jul 2016 14:36:01 +0800 zhongjiang <zhongjiang@huawei.com> wrote:
>
>> From: zhong jiang <zhongjiang@huawei.com>
>>
>> when image is loaded into kernel, we need set up page table for it.
>> and all valid pfn also set up new mapping. it will set up a pmd huge
>> entry if pud_present is true.  relocate_kernel points to code segment
>> can locate in the pmd huge entry in init_transtion_pgtable. therefore,
>> we need to take the situation into account.
> Sorry, I just don't understand this changelog.  The second sentence is
> particularly hard.
>
> So can you please have another attempt at preparing the changelog text?
> The resend the patches and this time be sure to Cc the kexec
> maintainers.  I suggest this list:
>
> Cc: kexec@lists.infradead.org
> Cc: Eric Biederman <ebiederm@xmission.com>
> Cc: Dave Young <dyoung@redhat.com>
> Cc: Vivek Goyal <vgoyal@redhat.com>
> Cc: Simon Horman <horms@verge.net.au>
>
>
> .
>
 ok ,  I will modify the changelog and resend to this list. thanks.

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Re: [PATCH 1/2] kexec: remove unnecessary unusable_pages

[zhong jiang]

On 2016/7/13 13:07, Eric W. Biederman wrote:
> zhong jiang <zhongjiang@huawei.com> writes:
>
>> On 2016/7/12 23:19, Eric W. Biederman wrote:
>>> zhongjiang <zhongjiang@huawei.com> writes:
>>>
>>>> From: zhong jiang <zhongjiang@huawei.com>
>>>>
>>>> In general, kexec alloc pages from buddy system, it cannot exceed
>>>> the physical address in the system.
>>>>
>>>> The patch just remove this unnecessary code, no functional change.
>>> On 32bit systems with highmem support kexec can very easily receive a
>>> page from the buddy allocator that can exceed 4GiB.  This doesn't show
>>> up on 64bit systems as typically the memory limits are less than the
>>> address space.  But this code is very necessary on some systems and
>>> removing it is not ok.
>>>
>>> Nacked-by: "Eric W. Biederman" <ebiederm@xmission.com>
>>>
>>   This viewpoint is as opposed to me,  32bit systems architectural decide it can not
>>   access exceed 4GiB whether the highmem or not.   but there is one exception, 
>>   when PAE enable, its physical address should be extended to 36,  new paging  mechanism
>>   established for it.  therefore, the  page from the buddy allocator
>>   can exceed 4GiB.
> Exactly.  And I was dealing with PAE systems in 2001 or so with > 4GiB
> of RAM.  Which is where the unusable_pages work comes from.
>
> Other architectures such as ARM also followed a similar path, so
> it isn't just x86 that has 32bit systems with > 32 address lines.
>
>>   moreover,  on 32bit systems I can not understand why KEXEC_SOURCE_MEMORY_LIMIT
>>   is defined to -1UL. therefore, kimge_aloc_page allocate page will always add to unusable_pages.
> -1UL is a short way of writing 0xffffffffUL  Which is as close as you
> can get to writing 0x100000000UL in 32bits.
>
> kimage_alloc_page won't always add to unusable_pages as there is memory
> below 4GiB but it isn't easily found so there may temporarily be a
> memory shortage, as it allocates it's way there.  Unfortunately whenever
> I have looked there are memory zones that line up with the memory the
> kexec is looking for.  So it does a little bit of a weird dance to get
> the memory it needs and to discard the memory it can't use.
>
> Eric
>
  Thanks , I get it.

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Re: [PATCH 1/2] kexec: remove unnecessary unusable_pages

[Eric W. Biederman]

zhong jiang <zhongjiang@huawei.com> writes:

> On 2016/7/12 23:19, Eric W. Biederman wrote:
>> zhongjiang <zhongjiang@huawei.com> writes:
>>
>>> From: zhong jiang <zhongjiang@huawei.com>
>>>
>>> In general, kexec alloc pages from buddy system, it cannot exceed
>>> the physical address in the system.
>>>
>>> The patch just remove this unnecessary code, no functional change.
>> On 32bit systems with highmem support kexec can very easily receive a
>> page from the buddy allocator that can exceed 4GiB.  This doesn't show
>> up on 64bit systems as typically the memory limits are less than the
>> address space.  But this code is very necessary on some systems and
>> removing it is not ok.
>>
>> Nacked-by: "Eric W. Biederman" <ebiederm@xmission.com>
>>
>   This viewpoint is as opposed to me,  32bit systems architectural decide it can not
>   access exceed 4GiB whether the highmem or not.   but there is one exception, 
>   when PAE enable, its physical address should be extended to 36,  new paging  mechanism
>   established for it.  therefore, the  page from the buddy allocator
>   can exceed 4GiB.

Exactly.  And I was dealing with PAE systems in 2001 or so with > 4GiB
of RAM.  Which is where the unusable_pages work comes from.

Other architectures such as ARM also followed a similar path, so
it isn't just x86 that has 32bit systems with > 32 address lines.

>   moreover,  on 32bit systems I can not understand why KEXEC_SOURCE_MEMORY_LIMIT
>   is defined to -1UL. therefore, kimge_aloc_page allocate page will always add to unusable_pages.

-1UL is a short way of writing 0xffffffffUL  Which is as close as you
can get to writing 0x100000000UL in 32bits.

kimage_alloc_page won't always add to unusable_pages as there is memory
below 4GiB but it isn't easily found so there may temporarily be a
memory shortage, as it allocates it's way there.  Unfortunately whenever
I have looked there are memory zones that line up with the memory the
kexec is looking for.  So it does a little bit of a weird dance to get
the memory it needs and to discard the memory it can't use.

Eric

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Re: [PATCH 1/2] kexec: remove unnecessary unusable_pages

[zhong jiang]

On 2016/7/12 23:19, Eric W. Biederman wrote:
> zhongjiang <zhongjiang@huawei.com> writes:
>
>> From: zhong jiang <zhongjiang@huawei.com>
>>
>> In general, kexec alloc pages from buddy system, it cannot exceed
>> the physical address in the system.
>>
>> The patch just remove this unnecessary code, no functional change.
> On 32bit systems with highmem support kexec can very easily receive a
> page from the buddy allocator that can exceed 4GiB.  This doesn't show
> up on 64bit systems as typically the memory limits are less than the
> address space.  But this code is very necessary on some systems and
> removing it is not ok.
>
> Nacked-by: "Eric W. Biederman" <ebiederm@xmission.com>
>
  This viewpoint is as opposed to me,  32bit systems architectural decide it can not
  access exceed 4GiB whether the highmem or not.   but there is one exception, 
  when PAE enable, its physical address should be extended to 36,  new paging  mechanism
  established for it.  therefore, the  page from the buddy allocator can exceed 4GiB.

  moreover,  on 32bit systems I can not understand why KEXEC_SOURCE_MEMORY_LIMIT
  is defined to -1UL. therefore, kimge_aloc_page allocate page will always add to unusable_pages.

  Thanks
  zhongjiang
>> Signed-off-by: zhong jiang <zhongjiang@huawei.com>
>> ---
>>  include/linux/kexec.h |  1 -
>>  kernel/kexec_core.c   | 13 -------------
>>  2 files changed, 14 deletions(-)
>>
>> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
>> index e8acb2b..26e4917 100644
>> --- a/include/linux/kexec.h
>> +++ b/include/linux/kexec.h
>> @@ -162,7 +162,6 @@ struct kimage {
>>  
>>  	struct list_head control_pages;
>>  	struct list_head dest_pages;
>> -	struct list_head unusable_pages;
>>  
>>  	/* Address of next control page to allocate for crash kernels. */
>>  	unsigned long control_page;
>> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
>> index 56b3ed0..448127d 100644
>> --- a/kernel/kexec_core.c
>> +++ b/kernel/kexec_core.c
>> @@ -257,9 +257,6 @@ struct kimage *do_kimage_alloc_init(void)
>>  	/* Initialize the list of destination pages */
>>  	INIT_LIST_HEAD(&image->dest_pages);
>>  
>> -	/* Initialize the list of unusable pages */
>> -	INIT_LIST_HEAD(&image->unusable_pages);
>> -
>>  	return image;
>>  }
>>  
>> @@ -517,10 +514,6 @@ static void kimage_free_extra_pages(struct kimage *image)
>>  {
>>  	/* Walk through and free any extra destination pages I may have */
>>  	kimage_free_page_list(&image->dest_pages);
>> -
>> -	/* Walk through and free any unusable pages I have cached */
>> -	kimage_free_page_list(&image->unusable_pages);
>> -
>>  }
>>  void kimage_terminate(struct kimage *image)
>>  {
>> @@ -647,12 +640,6 @@ static struct page *kimage_alloc_page(struct kimage *image,
>>  		page = kimage_alloc_pages(gfp_mask, 0);
>>  		if (!page)
>>  			return NULL;
>> -		/* If the page cannot be used file it away */
>> -		if (page_to_pfn(page) >
>> -				(KEXEC_SOURCE_MEMORY_LIMIT >> PAGE_SHIFT)) {
>> -			list_add(&page->lru, &image->unusable_pages);
>> -			continue;
>> -		}
>>  		addr = page_to_pfn(page) << PAGE_SHIFT;
>>  
>>  		/* If it is the destination page we want use it */
> .
>


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Re: [PATCH 1/2] kexec: remove unnecessary unusable_pages

[Eric W. Biederman]

zhongjiang <zhongjiang@huawei.com> writes:

> From: zhong jiang <zhongjiang@huawei.com>
>
> In general, kexec alloc pages from buddy system, it cannot exceed
> the physical address in the system.
>
> The patch just remove this unnecessary code, no functional change.

On 32bit systems with highmem support kexec can very easily receive a
page from the buddy allocator that can exceed 4GiB.  This doesn't show
up on 64bit systems as typically the memory limits are less than the
address space.  But this code is very necessary on some systems and
removing it is not ok.

Nacked-by: "Eric W. Biederman" <ebiederm@xmission.com>


>
> Signed-off-by: zhong jiang <zhongjiang@huawei.com>
> ---
>  include/linux/kexec.h |  1 -
>  kernel/kexec_core.c   | 13 -------------
>  2 files changed, 14 deletions(-)
>
> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
> index e8acb2b..26e4917 100644
> --- a/include/linux/kexec.h
> +++ b/include/linux/kexec.h
> @@ -162,7 +162,6 @@ struct kimage {
>  
>  	struct list_head control_pages;
>  	struct list_head dest_pages;
> -	struct list_head unusable_pages;
>  
>  	/* Address of next control page to allocate for crash kernels. */
>  	unsigned long control_page;
> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> index 56b3ed0..448127d 100644
> --- a/kernel/kexec_core.c
> +++ b/kernel/kexec_core.c
> @@ -257,9 +257,6 @@ struct kimage *do_kimage_alloc_init(void)
>  	/* Initialize the list of destination pages */
>  	INIT_LIST_HEAD(&image->dest_pages);
>  
> -	/* Initialize the list of unusable pages */
> -	INIT_LIST_HEAD(&image->unusable_pages);
> -
>  	return image;
>  }
>  
> @@ -517,10 +514,6 @@ static void kimage_free_extra_pages(struct kimage *image)
>  {
>  	/* Walk through and free any extra destination pages I may have */
>  	kimage_free_page_list(&image->dest_pages);
> -
> -	/* Walk through and free any unusable pages I have cached */
> -	kimage_free_page_list(&image->unusable_pages);
> -
>  }
>  void kimage_terminate(struct kimage *image)
>  {
> @@ -647,12 +640,6 @@ static struct page *kimage_alloc_page(struct kimage *image,
>  		page = kimage_alloc_pages(gfp_mask, 0);
>  		if (!page)
>  			return NULL;
> -		/* If the page cannot be used file it away */
> -		if (page_to_pfn(page) >
> -				(KEXEC_SOURCE_MEMORY_LIMIT >> PAGE_SHIFT)) {
> -			list_add(&page->lru, &image->unusable_pages);
> -			continue;
> -		}
>  		addr = page_to_pfn(page) << PAGE_SHIFT;
>  
>  		/* If it is the destination page we want use it */

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[PATCH 1/2] kexec: remove unnecessary unusable_pages

[zhongjiang]

From: zhong jiang <zhongjiang@huawei.com>

In general, kexec alloc pages from buddy system, it cannot exceed
the physical address in the system.

The patch just remove this unnecessary code, no functional change.

Signed-off-by: zhong jiang <zhongjiang@huawei.com>
---
 include/linux/kexec.h |  1 -
 kernel/kexec_core.c   | 13 -------------
 2 files changed, 14 deletions(-)

diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index e8acb2b..26e4917 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -162,7 +162,6 @@ struct kimage {
 
 	struct list_head control_pages;
 	struct list_head dest_pages;
-	struct list_head unusable_pages;
 
 	/* Address of next control page to allocate for crash kernels. */
 	unsigned long control_page;
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index 56b3ed0..448127d 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -257,9 +257,6 @@ struct kimage *do_kimage_alloc_init(void)
 	/* Initialize the list of destination pages */
 	INIT_LIST_HEAD(&image->dest_pages);
 
-	/* Initialize the list of unusable pages */
-	INIT_LIST_HEAD(&image->unusable_pages);
-
 	return image;
 }
 
@@ -517,10 +514,6 @@ static void kimage_free_extra_pages(struct kimage *image)
 {
 	/* Walk through and free any extra destination pages I may have */
 	kimage_free_page_list(&image->dest_pages);
-
-	/* Walk through and free any unusable pages I have cached */
-	kimage_free_page_list(&image->unusable_pages);
-
 }
 void kimage_terminate(struct kimage *image)
 {
@@ -647,12 +640,6 @@ static struct page *kimage_alloc_page(struct kimage *image,
 		page = kimage_alloc_pages(gfp_mask, 0);
 		if (!page)
 			return NULL;
-		/* If the page cannot be used file it away */
-		if (page_to_pfn(page) >
-				(KEXEC_SOURCE_MEMORY_LIMIT >> PAGE_SHIFT)) {
-			list_add(&page->lru, &image->unusable_pages);
-			continue;
-		}
 		addr = page_to_pfn(page) << PAGE_SHIFT;
 
 		/* If it is the destination page we want use it */
-- 
1.8.3.1

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