Re: [PATCH] x86: fix small LDT allocation for Xen

[Jan Beulich]

>>> On 01.09.15 at 21:37,  wrote:
> On Tue, Sep 1, 2015 at 3:48 AM, Jan Beulich  wrote:
>> While commit 37868fe113 ("x86/ldt: Make modify_ldt synchronous") added
>> a nice comment explaining that Xen needs page-aligned whole page chunks
>> for guest descriptor tables, it then nevertheless used kzalloc() on the
>> small size path. As I'm unaware of guarantees for kmalloc(PAGE_SIZE, )
>> to return page-aligned memory blocks, I believe this needs to be
>> switched back to __get_free_page().
>>
>> Signed-off-by: Jan Beulich 
>> Cc: Andy Lutomirski 
>> Cc: Boris Ostrovsky 
>> Cc: David Vrabel 
>> Cc: Konrad Rzeszutek Wilk 
>> ---
>>  arch/x86/kernel/ldt.c |2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> --- 4.2/arch/x86/kernel/ldt.c
>> +++ 4.2-x86-LDT-alloc/arch/x86/kernel/ldt.c
>> @@ -58,7 +58,7 @@ static struct ldt_struct *alloc_ldt_stru
>> if (alloc_size > PAGE_SIZE)
>> new_ldt->entries = vzalloc(alloc_size);
>> else
>> -   new_ldt->entries = kzalloc(PAGE_SIZE, GFP_KERNEL);
>> +   new_ldt->entries = (void 
>> *)__get_free_page(GFP_KERNEL|__GFP_ZERO);
> 
> This would need a corresponding change to the kfree path, right?

Oops - yes of course.

Jan

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Re: [PATCH] x86: fix small LDT allocation for Xen

[Jan Beulich]

>>> On 01.09.15 at 21:37,  wrote:
> On Tue, Sep 1, 2015 at 3:48 AM, Jan Beulich  wrote:
>> While commit 37868fe113 ("x86/ldt: Make modify_ldt synchronous") added
>> a nice comment explaining that Xen needs page-aligned whole page chunks
>> for guest descriptor tables, it then nevertheless used kzalloc() on the
>> small size path. As I'm unaware of guarantees for kmalloc(PAGE_SIZE, )
>> to return page-aligned memory blocks, I believe this needs to be
>> switched back to __get_free_page().
>>
>> Signed-off-by: Jan Beulich 
>> Cc: Andy Lutomirski 
>> Cc: Boris Ostrovsky 
>> Cc: David Vrabel 
>> Cc: Konrad Rzeszutek Wilk 
>> ---
>>  arch/x86/kernel/ldt.c |2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> --- 4.2/arch/x86/kernel/ldt.c
>> +++ 4.2-x86-LDT-alloc/arch/x86/kernel/ldt.c
>> @@ -58,7 +58,7 @@ static struct ldt_struct *alloc_ldt_stru
>> if (alloc_size > PAGE_SIZE)
>> new_ldt->entries = vzalloc(alloc_size);
>> else
>> -   new_ldt->entries = kzalloc(PAGE_SIZE, GFP_KERNEL);
>> +   new_ldt->entries = (void 
>> *)__get_free_page(GFP_KERNEL|__GFP_ZERO);
> 
> This would need a corresponding change to the kfree path, right?

Oops - yes of course.

Jan

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Re: [PATCH] x86: fix small LDT allocation for Xen

[Andy Lutomirski]

On Tue, Sep 1, 2015 at 3:48 AM, Jan Beulich  wrote:
> While commit 37868fe113 ("x86/ldt: Make modify_ldt synchronous") added
> a nice comment explaining that Xen needs page-aligned whole page chunks
> for guest descriptor tables, it then nevertheless used kzalloc() on the
> small size path. As I'm unaware of guarantees for kmalloc(PAGE_SIZE, )
> to return page-aligned memory blocks, I believe this needs to be
> switched back to __get_free_page().
>
> Signed-off-by: Jan Beulich 
> Cc: Andy Lutomirski 
> Cc: Boris Ostrovsky 
> Cc: David Vrabel 
> Cc: Konrad Rzeszutek Wilk 
> ---
>  arch/x86/kernel/ldt.c |2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> --- 4.2/arch/x86/kernel/ldt.c
> +++ 4.2-x86-LDT-alloc/arch/x86/kernel/ldt.c
> @@ -58,7 +58,7 @@ static struct ldt_struct *alloc_ldt_stru
> if (alloc_size > PAGE_SIZE)
> new_ldt->entries = vzalloc(alloc_size);
> else
> -   new_ldt->entries = kzalloc(PAGE_SIZE, GFP_KERNEL);
> +   new_ldt->entries = (void 
> *)__get_free_page(GFP_KERNEL|__GFP_ZERO);

This would need a corresponding change to the kfree path, right?

--Andy
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[PATCH] x86: fix small LDT allocation for Xen

[Jan Beulich]

While commit 37868fe113 ("x86/ldt: Make modify_ldt synchronous") added
a nice comment explaining that Xen needs page-aligned whole page chunks
for guest descriptor tables, it then nevertheless used kzalloc() on the
small size path. As I'm unaware of guarantees for kmalloc(PAGE_SIZE, )
to return page-aligned memory blocks, I believe this needs to be
switched back to __get_free_page().

Signed-off-by: Jan Beulich 
Cc: Andy Lutomirski 
Cc: Boris Ostrovsky 
Cc: David Vrabel 
Cc: Konrad Rzeszutek Wilk 
---
 arch/x86/kernel/ldt.c |2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- 4.2/arch/x86/kernel/ldt.c
+++ 4.2-x86-LDT-alloc/arch/x86/kernel/ldt.c
@@ -58,7 +58,7 @@ static struct ldt_struct *alloc_ldt_stru
if (alloc_size > PAGE_SIZE)
new_ldt->entries = vzalloc(alloc_size);
else
-   new_ldt->entries = kzalloc(PAGE_SIZE, GFP_KERNEL);
+   new_ldt->entries = (void 
*)__get_free_page(GFP_KERNEL|__GFP_ZERO);
 
if (!new_ldt->entries) {
kfree(new_ldt);



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Re: [PATCH] x86: fix small LDT allocation for Xen

[Andy Lutomirski]

On Tue, Sep 1, 2015 at 3:48 AM, Jan Beulich  wrote:
> While commit 37868fe113 ("x86/ldt: Make modify_ldt synchronous") added
> a nice comment explaining that Xen needs page-aligned whole page chunks
> for guest descriptor tables, it then nevertheless used kzalloc() on the
> small size path. As I'm unaware of guarantees for kmalloc(PAGE_SIZE, )
> to return page-aligned memory blocks, I believe this needs to be
> switched back to __get_free_page().
>
> Signed-off-by: Jan Beulich 
> Cc: Andy Lutomirski 
> Cc: Boris Ostrovsky 
> Cc: David Vrabel 
> Cc: Konrad Rzeszutek Wilk 
> ---
>  arch/x86/kernel/ldt.c |2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> --- 4.2/arch/x86/kernel/ldt.c
> +++ 4.2-x86-LDT-alloc/arch/x86/kernel/ldt.c
> @@ -58,7 +58,7 @@ static struct ldt_struct *alloc_ldt_stru
> if (alloc_size > PAGE_SIZE)
> new_ldt->entries = vzalloc(alloc_size);
> else
> -   new_ldt->entries = kzalloc(PAGE_SIZE, GFP_KERNEL);
> +   new_ldt->entries = (void 
> *)__get_free_page(GFP_KERNEL|__GFP_ZERO);

This would need a corresponding change to the kfree path, right?

--Andy
--
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[PATCH] x86: fix small LDT allocation for Xen

[Jan Beulich]

While commit 37868fe113 ("x86/ldt: Make modify_ldt synchronous") added
a nice comment explaining that Xen needs page-aligned whole page chunks
for guest descriptor tables, it then nevertheless used kzalloc() on the
small size path. As I'm unaware of guarantees for kmalloc(PAGE_SIZE, )
to return page-aligned memory blocks, I believe this needs to be
switched back to __get_free_page().

Signed-off-by: Jan Beulich 
Cc: Andy Lutomirski 
Cc: Boris Ostrovsky 
Cc: David Vrabel 
Cc: Konrad Rzeszutek Wilk 
---
 arch/x86/kernel/ldt.c |2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- 4.2/arch/x86/kernel/ldt.c
+++ 4.2-x86-LDT-alloc/arch/x86/kernel/ldt.c
@@ -58,7 +58,7 @@ static struct ldt_struct *alloc_ldt_stru
if (alloc_size > PAGE_SIZE)
new_ldt->entries = vzalloc(alloc_size);
else
-   new_ldt->entries = kzalloc(PAGE_SIZE, GFP_KERNEL);
+   new_ldt->entries = (void 
*)__get_free_page(GFP_KERNEL|__GFP_ZERO);
 
if (!new_ldt->entries) {
kfree(new_ldt);



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