* [PATCH v2] xen/x86: Zero out .bss for PV guests
@ 2016-02-24 15:19 Boris Ostrovsky
2016-02-24 16:05 ` Brian Gerst
2016-02-24 17:26 ` [Xen-devel] " Andrew Cooper
0 siblings, 2 replies; 5+ messages in thread
From: Boris Ostrovsky @ 2016-02-24 15:19 UTC (permalink / raw)
To: konrad.wilk, david.vrabel
Cc: xen-devel, linux-kernel, mcgrof, Boris Ostrovsky, stable
Baremetal kernels clear .bss early in the boot but Xen PV guests don't
execute that code. They have been able to run without problems because
Xen domain builder happens to give out zeroed pages. However, since this
is not really guaranteed, .bss should be explicitly cleared.
(Since we introduce macros for specifying 32- and 64-bit registers we
can get rid of ifdefs in startup_xen())
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: stable@vger.kernel.org
---
arch/x86/xen/xen-head.S | 29 ++++++++++++++++++++++-------
1 file changed, 22 insertions(+), 7 deletions(-)
diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
index b65f59a..2af87d1 100644
--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@@ -35,16 +35,31 @@
#define PVH_FEATURES (0)
#endif
- __INIT
-ENTRY(startup_xen)
- cld
#ifdef CONFIG_X86_32
- mov %esi,xen_start_info
- mov $init_thread_union+THREAD_SIZE,%esp
+#define REG(register) %e##register
+#define WSIZE_SHIFT 2
+#define STOS stosl
#else
- mov %rsi,xen_start_info
- mov $init_thread_union+THREAD_SIZE,%rsp
+#define REG(register) %r##register
+#define WSIZE_SHIFT 3
+#define STOS stosq
#endif
+
+ __INIT
+ENTRY(startup_xen)
+ cld
+
+ /* Clear .bss */
+ xor REG(ax),REG(ax)
+ mov $__bss_start,REG(di)
+ mov $__bss_stop,REG(cx)
+ sub REG(di),REG(cx)
+ shr $WSIZE_SHIFT,REG(cx)
+ rep STOS
+
+ mov REG(si),xen_start_info
+ mov $init_thread_union+THREAD_SIZE,REG(sp)
+
jmp xen_start_kernel
__FINIT
--
2.1.0
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH v2] xen/x86: Zero out .bss for PV guests
2016-02-24 15:19 [PATCH v2] xen/x86: Zero out .bss for PV guests Boris Ostrovsky
@ 2016-02-24 16:05 ` Brian Gerst
2016-02-24 16:33 ` Boris Ostrovsky
2016-02-24 17:26 ` [Xen-devel] " Andrew Cooper
1 sibling, 1 reply; 5+ messages in thread
From: Brian Gerst @ 2016-02-24 16:05 UTC (permalink / raw)
To: Boris Ostrovsky
Cc: Konrad Rzeszutek Wilk, David Vrabel, xen-devel,
Linux Kernel Mailing List, mcgrof, stable
On Wed, Feb 24, 2016 at 10:19 AM, Boris Ostrovsky
<boris.ostrovsky@oracle.com> wrote:
> Baremetal kernels clear .bss early in the boot but Xen PV guests don't
> execute that code. They have been able to run without problems because
> Xen domain builder happens to give out zeroed pages. However, since this
> is not really guaranteed, .bss should be explicitly cleared.
>
> (Since we introduce macros for specifying 32- and 64-bit registers we
> can get rid of ifdefs in startup_xen())
>
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> Cc: stable@vger.kernel.org
> ---
> arch/x86/xen/xen-head.S | 29 ++++++++++++++++++++++-------
> 1 file changed, 22 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
> index b65f59a..2af87d1 100644
> --- a/arch/x86/xen/xen-head.S
> +++ b/arch/x86/xen/xen-head.S
> @@ -35,16 +35,31 @@
> #define PVH_FEATURES (0)
> #endif
>
> - __INIT
> -ENTRY(startup_xen)
> - cld
> #ifdef CONFIG_X86_32
> - mov %esi,xen_start_info
> - mov $init_thread_union+THREAD_SIZE,%esp
> +#define REG(register) %e##register
> +#define WSIZE_SHIFT 2
> +#define STOS stosl
> #else
> - mov %rsi,xen_start_info
> - mov $init_thread_union+THREAD_SIZE,%rsp
> +#define REG(register) %r##register
> +#define WSIZE_SHIFT 3
> +#define STOS stosq
> #endif
> +
> + __INIT
> +ENTRY(startup_xen)
> + cld
> +
> + /* Clear .bss */
> + xor REG(ax),REG(ax)
> + mov $__bss_start,REG(di)
> + mov $__bss_stop,REG(cx)
> + sub REG(di),REG(cx)
> + shr $WSIZE_SHIFT,REG(cx)
> + rep STOS
> +
> + mov REG(si),xen_start_info
> + mov $init_thread_union+THREAD_SIZE,REG(sp)
> +
> jmp xen_start_kernel
>
> __FINIT
Use the macros in <asm/asm.h> instead of defining your own. Also,
xorl %eax,%eax is good for 64-bit too, since the upper bits are
cleared.
--
Brian Gerst
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v2] xen/x86: Zero out .bss for PV guests
2016-02-24 16:05 ` Brian Gerst
@ 2016-02-24 16:33 ` Boris Ostrovsky
0 siblings, 0 replies; 5+ messages in thread
From: Boris Ostrovsky @ 2016-02-24 16:33 UTC (permalink / raw)
To: Brian Gerst
Cc: Konrad Rzeszutek Wilk, David Vrabel, xen-devel,
Linux Kernel Mailing List, mcgrof, stable
On 02/24/2016 11:05 AM, Brian Gerst wrote:
>
> Use the macros in <asm/asm.h> instead of defining your own. Also,
> xorl %eax,%eax is good for 64-bit too, since the upper bits are
> cleared.
I suspected this would have to be defined somewhere but couldn't find
it. Thanks!
-boris
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [Xen-devel] [PATCH v2] xen/x86: Zero out .bss for PV guests
2016-02-24 15:19 [PATCH v2] xen/x86: Zero out .bss for PV guests Boris Ostrovsky
2016-02-24 16:05 ` Brian Gerst
@ 2016-02-24 17:26 ` Andrew Cooper
2016-02-24 17:48 ` Boris Ostrovsky
1 sibling, 1 reply; 5+ messages in thread
From: Andrew Cooper @ 2016-02-24 17:26 UTC (permalink / raw)
To: Boris Ostrovsky, konrad.wilk, david.vrabel
Cc: xen-devel, mcgrof, linux-kernel, stable
On 24/02/16 15:19, Boris Ostrovsky wrote:
> Baremetal kernels clear .bss early in the boot but Xen PV guests don't
> execute that code. They have been able to run without problems because
> Xen domain builder happens to give out zeroed pages. However, since this
> is not really guaranteed, .bss should be explicitly cleared.
>
> (Since we introduce macros for specifying 32- and 64-bit registers we
> can get rid of ifdefs in startup_xen())
>
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> Cc: stable@vger.kernel.org
> ---
> arch/x86/xen/xen-head.S | 29 ++++++++++++++++++++++-------
> 1 file changed, 22 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
> index b65f59a..2af87d1 100644
> --- a/arch/x86/xen/xen-head.S
> +++ b/arch/x86/xen/xen-head.S
> @@ -35,16 +35,31 @@
> #define PVH_FEATURES (0)
> #endif
>
> - __INIT
> -ENTRY(startup_xen)
> - cld
> #ifdef CONFIG_X86_32
> - mov %esi,xen_start_info
> - mov $init_thread_union+THREAD_SIZE,%esp
> +#define REG(register) %e##register
> +#define WSIZE_SHIFT 2
> +#define STOS stosl
> #else
> - mov %rsi,xen_start_info
> - mov $init_thread_union+THREAD_SIZE,%rsp
> +#define REG(register) %r##register
> +#define WSIZE_SHIFT 3
> +#define STOS stosq
> #endif
> +
> + __INIT
> +ENTRY(startup_xen)
> + cld
> +
> + /* Clear .bss */
> + xor REG(ax),REG(ax)
If we are nitpicking,
This should be xor %eax, %eax even in 64bit. Functionally identical,
and shorter to encode.
~Andrew
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [Xen-devel] [PATCH v2] xen/x86: Zero out .bss for PV guests
2016-02-24 17:26 ` [Xen-devel] " Andrew Cooper
@ 2016-02-24 17:48 ` Boris Ostrovsky
0 siblings, 0 replies; 5+ messages in thread
From: Boris Ostrovsky @ 2016-02-24 17:48 UTC (permalink / raw)
To: Andrew Cooper, konrad.wilk, david.vrabel
Cc: xen-devel, mcgrof, linux-kernel, stable
On 02/24/2016 12:26 PM, Andrew Cooper wrote:
> On 24/02/16 15:19, Boris Ostrovsky wrote:
>> + /* Clear .bss */
>> + xor REG(ax),REG(ax)
> If we are nitpicking,
>
> This should be xor %eax, %eax even in 64bit. Functionally identical,
> and shorter to encode.
Right, Brian Gerst pointed this out too in another message.
-boris
^ permalink raw reply [flat|nested] 5+ messages in thread
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2016-02-24 15:19 [PATCH v2] xen/x86: Zero out .bss for PV guests Boris Ostrovsky
2016-02-24 16:05 ` Brian Gerst
2016-02-24 16:33 ` Boris Ostrovsky
2016-02-24 17:26 ` [Xen-devel] " Andrew Cooper
2016-02-24 17:48 ` Boris Ostrovsky
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