Re: linux-next: Tree for Mar 25 (arch/x86/kvm/)

[Paolo Bonzini]

On 25/03/20 16:30, Randy Dunlap wrote:
> 24 (only showing one of them here) BUILD_BUG() errors in arch/x86/kvm/cpuid.h
> function __cpuid_entry_get_reg(), for the default: case.
> 
> 
>   CC      arch/x86/kvm/cpuid.o
> In file included from ../include/linux/export.h:43:0,
>                  from ../include/linux/linkage.h:7,
>                  from ../include/linux/preempt.h:10,
>                  from ../include/linux/hardirq.h:5,
>                  from ../include/linux/kvm_host.h:7,
>                  from ../arch/x86/kvm/cpuid.c:12:
> In function â__cpuid_entry_get_regâ,
>     inlined from âkvm_cpu_cap_maskâ at ../arch/x86/kvm/cpuid.c:272:25,
>     inlined from âkvm_set_cpu_capsâ at ../arch/x86/kvm/cpuid.c:292:2:
> ../include/linux/compiler.h:394:38: error: call to â__compiletime_assert_114â declared with attribute error: BUILD_BUG failed
>   _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
>                                       ^
> ../include/linux/compiler.h:375:4: note: in definition of macro â__compiletime_assertâ
>     prefix ## suffix();    \
>     ^~~~~~
> ../include/linux/compiler.h:394:2: note: in expansion of macro â_compiletime_assertâ
>   _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
>   ^~~~~~~~~~~~~~~~~~~
> ../include/linux/build_bug.h:39:37: note: in expansion of macro âcompiletime_assertâ
>  #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
>                                      ^~~~~~~~~~~~~~~~~~
> ../include/linux/build_bug.h:59:21: note: in expansion of macro âBUILD_BUG_ON_MSGâ
>  #define BUILD_BUG() BUILD_BUG_ON_MSG(1, "BUILD_BUG failed")
>                      ^~~~~~~~~~~~~~~~
> ../arch/x86/kvm/cpuid.h:114:3: note: in expansion of macro âBUILD_BUGâ
>    BUILD_BUG();
>    ^~~~~~~~~
> 

Looks like the compiler is not smart enough to figure out the constant 
expressions in BUILD_BUG.  I think we need to do something like this:

diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
index 23b4cd1ad986..8f711b0cdec0 100644
--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -40,6 +40,7 @@ struct cpuid_reg {
 	int reg;
 };
 
+/* Update reverse_cpuid_check as well when adding an entry.  */
 static const struct cpuid_reg reverse_cpuid[] = {
 	[CPUID_1_EDX]         = {         1, 0, CPUID_EDX},
 	[CPUID_8000_0001_EDX] = {0x80000001, 0, CPUID_EDX},
@@ -68,12 +69,21 @@ static const struct cpuid_reg reverse_cpuid[] = {
  */
 static __always_inline void reverse_cpuid_check(unsigned int x86_leaf)
 {
-	BUILD_BUG_ON(x86_leaf == CPUID_LNX_1);
-	BUILD_BUG_ON(x86_leaf == CPUID_LNX_2);
-	BUILD_BUG_ON(x86_leaf == CPUID_LNX_3);
-	BUILD_BUG_ON(x86_leaf == CPUID_LNX_4);
-	BUILD_BUG_ON(x86_leaf >= ARRAY_SIZE(reverse_cpuid));
-	BUILD_BUG_ON(reverse_cpuid[x86_leaf].function == 0);
+	BUILD_BUG_ON(x86_leaf != CPUID_1_EDX &&
+	             x86_leaf != CPUID_8000_0001_EDX &&
+	             x86_leaf != CPUID_8086_0001_EDX &&
+	             x86_leaf != CPUID_1_ECX &&
+	             x86_leaf != CPUID_C000_0001_EDX &&
+	             x86_leaf != CPUID_8000_0001_ECX &&
+	             x86_leaf != CPUID_7_0_EBX &&
+	             x86_leaf != CPUID_D_1_EAX &&
+	             x86_leaf != CPUID_8000_0008_EBX &&
+	             x86_leaf != CPUID_6_EAX &&
+	             x86_leaf != CPUID_8000_000A_EDX &&
+	             x86_leaf != CPUID_7_ECX &&
+	             x86_leaf != CPUID_8000_0007_EBX &&
+	             x86_leaf != CPUID_7_EDX &&
+	             x86_leaf != CPUID_7_1_EAX);
 }
 
 /*

Randy, can you test it with your compiler?

Thanks,

Paolo