powerpc/mm: Handle removing maybe-present bolted HPTEs

At the moment the hpte_removebolted callback in ppc_md returns void and
will BUG_ON() if the hpte it's asked to remove doesn't exist in the first
place.  This is awkward for the case of cleaning up a mapping which was
partially made before failing.

So, we add a return value to hpte_removebolted, and have it return ENOENT
in the case that the HPTE to remove didn't exist in the first place.

In the (sole) caller, we propagate errors in hpte_removebolted to its
caller to handle.  However, we handle ENOENT specially, continuing to
complete the unmapping over the specified range before returning the error
to the caller.

This means that htab_remove_mapping() will work sanely on a partially
present mapping, removing any HPTEs which are present, while also returning
ENOENT to its caller in case it's important there.

There are two callers of htab_remove_mapping():
   - In remove_section_mapping() we already WARN_ON() any error return,
     which is reasonable - in this case the mapping should be fully
     present
   - In vmemmap_remove_mapping() we BUG_ON() any error.  We change that to
     just a WARN_ON() in the case of ENOENT, since failing to remove a
     mapping that wasn't there in the first place probably shouldn't be
     fatal.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/machdep.h

@@ -54,7 +54,7 @@ struct machdep_calls {
 				       int psize, int apsize,
 				       int ssize);
 	long		(*hpte_remove)(unsigned long hpte_group);
-	void            (*hpte_removebolted)(unsigned long ea,
+	int             (*hpte_removebolted)(unsigned long ea,
 					     int psize, int ssize);
 	void		(*flush_hash_range)(unsigned long number, int local);
 	void		(*hugepage_invalidate)(unsigned long vsid,

arch/powerpc/mm/hash_utils_64.c

@@ -269,17 +269,26 @@ int htab_remove_mapping(unsigned long vstart, unsigned long vend,
 {
 	unsigned long vaddr;
 	unsigned int step, shift;
+	int rc;
+	int ret = 0;
 
 	shift = mmu_psize_defs[psize].shift;
 	step = 1 << shift;
 
 	if (!ppc_md.hpte_removebolted)
 		return -ENODEV;
 
-	for (vaddr = vstart; vaddr < vend; vaddr += step)
-		ppc_md.hpte_removebolted(vaddr, psize, ssize);
+	for (vaddr = vstart; vaddr < vend; vaddr += step) {
+		rc = ppc_md.hpte_removebolted(vaddr, psize, ssize);
+		if (rc == -ENOENT) {
+			ret = -ENOENT;
+			continue;
+		}
+		if (rc < 0)
+			return rc;
+	}
 
-	return 0;
+	return ret;
 }
 #endif /* CONFIG_MEMORY_HOTPLUG */
 

arch/powerpc/mm/init_64.c

@@ -232,10 +232,11 @@ static void __meminit vmemmap_create_mapping(unsigned long start,
 static void vmemmap_remove_mapping(unsigned long start,
 				   unsigned long page_size)
 {
-	int mapped = htab_remove_mapping(start, start + page_size,
-					 mmu_vmemmap_psize,
-					 mmu_kernel_ssize);
-	BUG_ON(mapped < 0);
+	int rc = htab_remove_mapping(start, start + page_size,
+				     mmu_vmemmap_psize,
+				     mmu_kernel_ssize);
+	BUG_ON((rc < 0) && (rc != -ENOENT));
+	WARN_ON(rc == -ENOENT);
 }
 #endif
 

arch/powerpc/platforms/pseries/lpar.c

@@ -505,8 +505,8 @@ static void pSeries_lpar_hugepage_invalidate(unsigned long vsid,
 }
 #endif
 
-static void pSeries_lpar_hpte_removebolted(unsigned long ea,
-					   int psize, int ssize)
+static int pSeries_lpar_hpte_removebolted(unsigned long ea,
+					  int psize, int ssize)
 {
 	unsigned long vpn;
 	unsigned long slot, vsid;
@@ -515,11 +515,14 @@ static void pSeries_lpar_hpte_removebolted(unsigned long ea,
 	vpn = hpt_vpn(ea, vsid, ssize);
 
 	slot = pSeries_lpar_hpte_find(vpn, psize, ssize);
-	BUG_ON(slot == -1);
+	if (slot == -1)
+		return -ENOENT;
+
 	/*
 	 * lpar doesn't use the passed actual page size
 	 */
 	pSeries_lpar_hpte_invalidate(slot, vpn, psize, 0, ssize, 0);
+	return 0;
 }
 
 /*