[PATCH] constify microcode hypercall argument

[PATCH] constify microcode hypercall argument

[Jan Beulich]

Linux 2.6.27 marks the data pointer in its firmware struct 'const', and
hence, to avoid a compiler warning, Xen's microcode update interface
should be properly properly constified too.

Signed-off-by: Jan Beulich <jbeulich@novell.com>

Index: 2008-08-06/xen/arch/x86/microcode.c
===================================================================
--- 2008-08-06.orig/xen/arch/x86/microcode.c	2008-06-12 09:20:38.000000000 +0200
+++ 2008-08-06/xen/arch/x86/microcode.c	2008-08-20 12:33:03.000000000 +0200
@@ -124,7 +124,7 @@ boolean_param("microcode.verbose", verbo
 /* no concurrent ->write()s are allowed on /dev/cpu/microcode */
 static DEFINE_MUTEX(microcode_mutex);
 
-static void __user *user_buffer;	/* user area microcode data buffer */
+static const void __user *user_buffer;	/* user area microcode data buffer */
 static unsigned int user_buffer_size;	/* it's size */
 
 typedef enum mc_error_code {
@@ -455,7 +455,7 @@ static int do_microcode_update (void)
 	return error;
 }
 
-int microcode_update(XEN_GUEST_HANDLE(void) buf, unsigned long len)
+int microcode_update(XEN_GUEST_HANDLE(const_void) buf, unsigned long len)
 {
 	int ret;
 
Index: 2008-08-06/xen/arch/x86/platform_hypercall.c
===================================================================
--- 2008-08-06.orig/xen/arch/x86/platform_hypercall.c	2008-08-01 08:48:42.000000000 +0200
+++ 2008-08-06/xen/arch/x86/platform_hypercall.c	2008-08-20 12:34:23.000000000 +0200
@@ -147,8 +147,7 @@ ret_t do_platform_op(XEN_GUEST_HANDLE(xe
 
     case XENPF_microcode_update:
     {
-        extern int microcode_update(XEN_GUEST_HANDLE(void), unsigned long len);
-        XEN_GUEST_HANDLE(void) data;
+        XEN_GUEST_HANDLE(const_void) data;
 
         ret = xsm_microcode();
         if ( ret )
Index: 2008-08-06/xen/include/asm-x86/processor.h
===================================================================
--- 2008-08-06.orig/xen/include/asm-x86/processor.h	2008-05-07 12:21:37.000000000 +0200
+++ 2008-08-06/xen/include/asm-x86/processor.h	2008-08-20 12:34:43.000000000 +0200
@@ -583,6 +583,8 @@ int rdmsr_hypervisor_regs(
 int wrmsr_hypervisor_regs(
     uint32_t idx, uint32_t eax, uint32_t edx);
 
+int microcode_update(XEN_GUEST_HANDLE(const_void), unsigned long len);
+
 #endif /* !__ASSEMBLY__ */
 
 #endif /* __ASM_X86_PROCESSOR_H */
Index: 2008-08-06/xen/include/public/platform.h
===================================================================
--- 2008-08-06.orig/xen/include/public/platform.h	2008-05-15 14:51:17.000000000 +0200
+++ 2008-08-06/xen/include/public/platform.h	2008-08-20 12:30:50.000000000 +0200
@@ -97,7 +97,7 @@ DEFINE_XEN_GUEST_HANDLE(xenpf_read_memty
 #define XENPF_microcode_update    35
 struct xenpf_microcode_update {
     /* IN variables. */
-    XEN_GUEST_HANDLE(void) data;      /* Pointer to microcode data */
+    XEN_GUEST_HANDLE(const_void) data;/* Pointer to microcode data */
     uint32_t length;                  /* Length of microcode data. */
 };
 typedef struct xenpf_microcode_update xenpf_microcode_update_t;
Index: 2008-08-06/xen/include/xen/compat.h
===================================================================
--- 2008-08-06.orig/xen/include/xen/compat.h	2008-06-16 10:43:34.000000000 +0200
+++ 2008-08-06/xen/include/xen/compat.h	2008-08-20 13:57:27.000000000 +0200
@@ -19,7 +19,9 @@
         type *_[0] __attribute__((__packed__)); \
     } __compat_handle_ ## name
 
-#define DEFINE_COMPAT_HANDLE(name)   __DEFINE_COMPAT_HANDLE(name, name)
+#define DEFINE_COMPAT_HANDLE(name) \
+    __DEFINE_COMPAT_HANDLE(name, name); \
+    __DEFINE_COMPAT_HANDLE(const_ ## name, const name)
 #define COMPAT_HANDLE(name)          __compat_handle_ ## name
 
 /* Is the compat handle a NULL reference? */

Re: [PATCH] constify microcode hypercall argument

[Christoph Egger]

On Friday 29 August 2008 14:33:08 Jan Beulich wrote:
> Linux 2.6.27 marks the data pointer in its firmware struct 'const', and
> hence, to avoid a compiler warning, Xen's microcode update interface
> should be properly properly constified too.

What makes you confident, that this reason applies to other operating systems
(Solaris, BSD) , too ?

Christoph


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Re: [PATCH] constify microcode hypercall argument

[Jan Beulich]

>>> Christoph Egger <Christoph.Egger@amd.com> 29.08.08 15:55 >>>
>On Friday 29 August 2008 14:33:08 Jan Beulich wrote:
>> Linux 2.6.27 marks the data pointer in its firmware struct 'const', and
>> hence, to avoid a compiler warning, Xen's microcode update interface
>> should be properly properly constified too.
>
>What makes you confident, that this reason applies to other operating systems
>(Solaris, BSD) , too ?

Adding 'const' on the consumer side is always safe, as long as the consumer
guarantees it won't violate the promise. The consumer here is Xen, so
there are no worries about individual guest OSes.

Jan