vmalloc: replace VM_NO_HUGE_VMAP with VM_ALLOW_HUGE_VMAP

Huge page backed vmalloc memory could benefit performance in many cases.
However, some users of vmalloc may not be ready to handle huge pages for
various reasons: hardware constraints, potential pages split, etc.
VM_NO_HUGE_VMAP was introduced to allow vmalloc users to opt-out huge
pages.  However, it is not easy to track down all the users that require
the opt-out, as the allocation are passed different stacks and may cause
issues in different layers.

To address this issue, replace VM_NO_HUGE_VMAP with an opt-in flag,
VM_ALLOW_HUGE_VMAP, so that users that benefit from huge pages could ask
specificially.

Also, remove vmalloc_no_huge() and add opt-in helper vmalloc_huge().

Fixes: fac54e2 ("x86/Kconfig: Select HAVE_ARCH_HUGE_VMALLOC with HAVE_ARCH_HUGE_VMAP")
Link: https://lore.kernel.org/netdev/[email protected]/"
Reviewed-by: Christoph Hellwig <[email protected]>
Signed-off-by: Song Liu <[email protected]>
Reviewed-by: Rik van Riel <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

arch/Kconfig

@@ -854,10 +854,8 @@ config HAVE_ARCH_HUGE_VMAP
 
 #
 #  Archs that select this would be capable of PMD-sized vmaps (i.e.,
-#  arch_vmap_pmd_supported() returns true), and they must make no assumptions
-#  that vmalloc memory is mapped with PAGE_SIZE ptes. The VM_NO_HUGE_VMAP flag
-#  can be used to prohibit arch-specific allocations from using hugepages to
-#  help with this (e.g., modules may require it).
+#  arch_vmap_pmd_supported() returns true). The VM_ALLOW_HUGE_VMAP flag
+#  must be used to enable allocations to use hugepages.
 #
 config HAVE_ARCH_HUGE_VMALLOC
 	depends on HAVE_ARCH_HUGE_VMAP

arch/powerpc/kernel/module.c

@@ -101,7 +101,7 @@ __module_alloc(unsigned long size, unsigned long start, unsigned long end, bool
 	 * too.
 	 */
 	return __vmalloc_node_range(size, 1, start, end, gfp, prot,
-				    VM_FLUSH_RESET_PERMS | VM_NO_HUGE_VMAP,
+				    VM_FLUSH_RESET_PERMS,
 				    NUMA_NO_NODE, __builtin_return_address(0));
 }
 

arch/s390/kvm/pv.c

@@ -137,12 +137,7 @@ static int kvm_s390_pv_alloc_vm(struct kvm *kvm)
 	/* Allocate variable storage */
 	vlen = ALIGN(virt * ((npages * PAGE_SIZE) / HPAGE_SIZE), PAGE_SIZE);
 	vlen += uv_info.guest_virt_base_stor_len;
-	/*
-	 * The Create Secure Configuration Ultravisor Call does not support
-	 * using large pages for the virtual memory area.
-	 * This is a hardware limitation.
-	 */
-	kvm->arch.pv.stor_var = vmalloc_no_huge(vlen);
+	kvm->arch.pv.stor_var = vzalloc(vlen);
 	if (!kvm->arch.pv.stor_var)
 		goto out_err;
 	return 0;

include/linux/vmalloc.h

@@ -26,7 +26,7 @@ struct notifier_block;		/* in notifier.h */
 #define VM_KASAN		0x00000080      /* has allocated kasan shadow memory */
 #define VM_FLUSH_RESET_PERMS	0x00000100	/* reset direct map and flush TLB on unmap, can't be freed in atomic context */
 #define VM_MAP_PUT_PAGES	0x00000200	/* put pages and free array in vfree */
-#define VM_NO_HUGE_VMAP		0x00000400	/* force PAGE_SIZE pte mapping */
+#define VM_ALLOW_HUGE_VMAP	0x00000400      /* Allow for huge pages on archs with HAVE_ARCH_HUGE_VMALLOC */
 
 #if (defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)) && \
 	!defined(CONFIG_KASAN_VMALLOC)
@@ -153,7 +153,7 @@ extern void *__vmalloc_node_range(unsigned long size, unsigned long align,
 			const void *caller) __alloc_size(1);
 void *__vmalloc_node(unsigned long size, unsigned long align, gfp_t gfp_mask,
 		int node, const void *caller) __alloc_size(1);
-void *vmalloc_no_huge(unsigned long size) __alloc_size(1);
+void *vmalloc_huge(unsigned long size, gfp_t gfp_mask) __alloc_size(1);
 
 extern void *__vmalloc_array(size_t n, size_t size, gfp_t flags) __alloc_size(1, 2);
 extern void *vmalloc_array(size_t n, size_t size) __alloc_size(1, 2);

mm/vmalloc.c

@@ -3095,7 +3095,7 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
 		return NULL;
 	}
 
-	if (vmap_allow_huge && !(vm_flags & VM_NO_HUGE_VMAP)) {
+	if (vmap_allow_huge && (vm_flags & VM_ALLOW_HUGE_VMAP)) {
 		unsigned long size_per_node;
 
 		/*
@@ -3262,21 +3262,24 @@ void *vmalloc(unsigned long size)
 EXPORT_SYMBOL(vmalloc);
 
 /**
- * vmalloc_no_huge - allocate virtually contiguous memory using small pages
- * @size:    allocation size
+ * vmalloc_huge - allocate virtually contiguous memory, allow huge pages
+ * @size:      allocation size
+ * @gfp_mask:  flags for the page level allocator
  *
- * Allocate enough non-huge pages to cover @size from the page level
+ * Allocate enough pages to cover @size from the page level
  * allocator and map them into contiguous kernel virtual space.
+ * If @size is greater than or equal to PMD_SIZE, allow using
+ * huge pages for the memory
  *
  * Return: pointer to the allocated memory or %NULL on error
  */
-void *vmalloc_no_huge(unsigned long size)
+void *vmalloc_huge(unsigned long size, gfp_t gfp_mask)
 {
 	return __vmalloc_node_range(size, 1, VMALLOC_START, VMALLOC_END,
-				    GFP_KERNEL, PAGE_KERNEL, VM_NO_HUGE_VMAP,
+				    gfp_mask, PAGE_KERNEL, VM_ALLOW_HUGE_VMAP,
 				    NUMA_NO_NODE, __builtin_return_address(0));
 }
-EXPORT_SYMBOL(vmalloc_no_huge);
+EXPORT_SYMBOL_GPL(vmalloc_huge);
 
 /**
  * vzalloc - allocate virtually contiguous memory with zero fill