powerpc/mm: Move the WARN() out of bad_kuap_fault()

In order to prepare the removal of calls to
search_exception_tables() on the fast path, move the
WARN() out of bad_kuap_fault().
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/9501311014bd6507e04b27a0c3035186ccf65cd5.1607491748.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/book3s/32/kup.h

@@ -183,11 +183,7 @@ bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write)
 	unsigned long begin = regs->kuap & 0xf0000000;
 	unsigned long end = regs->kuap << 28;
 
-	if (!is_write)
-		return false;
-
-	return WARN(address < begin || address >= end,
-		    "Bug: write fault blocked by segment registers !");
+	return is_write && (address < begin || address >= end);
 }
 
 #endif /* CONFIG_PPC_KUAP */

arch/powerpc/include/asm/book3s/64/kup.h

@@ -371,11 +371,9 @@ static inline bool bad_kuap_fault(struct pt_regs *regs, unsigned long address,
 	 * the AMR. Hence check for BLOCK_WRITE/READ against AMR.
 	 */
 	if (is_write) {
-		return WARN(((regs->amr & AMR_KUAP_BLOCK_WRITE) == AMR_KUAP_BLOCK_WRITE),
-			    "Bug: Write fault blocked by AMR!");
+		return (regs->amr & AMR_KUAP_BLOCK_WRITE) == AMR_KUAP_BLOCK_WRITE;
 	}
-	return WARN(((regs->amr & AMR_KUAP_BLOCK_READ) == AMR_KUAP_BLOCK_READ),
-		    "Bug: Read fault blocked by AMR!");
+	return (regs->amr & AMR_KUAP_BLOCK_READ) == AMR_KUAP_BLOCK_READ;
 }
 
 static __always_inline void allow_user_access(void __user *to, const void __user *from,

arch/powerpc/include/asm/nohash/32/kup-8xx.h

@@ -63,8 +63,7 @@ static inline void restore_user_access(unsigned long flags)
 static inline bool
 bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write)
 {
-	return WARN(!((regs->kuap ^ MD_APG_KUAP) & 0xff000000),
-		    "Bug: fault blocked by AP register !");
+	return !((regs->kuap ^ MD_APG_KUAP) & 0xff000000);
 }
 
 #endif /* !__ASSEMBLY__ */

arch/powerpc/mm/fault.c

@@ -228,7 +228,7 @@ static bool bad_kernel_fault(struct pt_regs *regs, unsigned long error_code,
 	// Read/write fault in a valid region (the exception table search passed
 	// above), but blocked by KUAP is bad, it can never succeed.
 	if (bad_kuap_fault(regs, address, is_write))
-		return true;
+		return WARN(true, "Bug: %s fault blocked by KUAP!", is_write ? "Write" : "Read");
 
 	// What's left? Kernel fault on user in well defined regions (extable
 	// matched), and allowed by KUAP in the faulting context.