[PATCH v3 1/4] mm/vmalloc: warn on invalid vmalloc gfp flags

Vishal Moola (Oracle)
2025-11-17T17:37:30Z

Vmalloc explicitly supports a list of flags, but we never enforce them.
vmalloc has been trying to handle unsupported flags by clearing and
setting flags wherever necessary. This is messy and makes the code
harder to understand, when we could simply check for a supported input
immediately instead.

Define a helper mask and function telling callers they have passed in
invalid flags, and clear those unsupported vmalloc flags.

Suggested-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
mm/vmalloc.c | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 0832f944544c..5dc467c6cab4 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -3911,6 +3911,28 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
return NULL;
}

+/*
+ * See __vmalloc_node_range() for a clear list of supported vmalloc flags.
+ * This gfp lists all flags currently passed through vmalloc. Currently,
+ * __GFP_ZERO is used by BPF and __GFP_NORETRY is used by percpu. Both drm
+ * and BPF also use GFP_USER. Additionally, various users pass
+ * GFP_KERNEL_ACCOUNT.
+ */
+#define GFP_VMALLOC_SUPPORTED (GFP_KERNEL | GFP_ATOMIC | GFP_NOWAIT |\
+ __GFP_NOFAIL | __GFP_ZERO | __GFP_NORETRY |\
+ GFP_NOFS | GFP_NOIO | GFP_KERNEL_ACCOUNT |\
+ GFP_USER)
+
+static gfp_t vmalloc_fix_flags(gfp_t flags)
+{
+ gfp_t invalid_mask = flags & ~GFP_VMALLOC_SUPPORTED;
+
+ flags &= GFP_VMALLOC_SUPPORTED;
+ WARN(1, "Unexpected gfp: %#x (%pGg). Fixing up to gfp: %#x (%pGg). Fix your code!\n",
+ invalid_mask, &invalid_mask, flags, &flags);
+ return flags;
+}
+
/**
* __vmalloc_node_range - allocate virtually contiguous memory
* @size: allocation size
@@ -4092,6 +4114,8 @@ EXPORT_SYMBOL_GPL(__vmalloc_node_noprof);

void *__vmalloc_noprof(unsigned long size, gfp_t gfp_mask)
{
+ if (unlikely(gfp_mask & ~GFP_VMALLOC_SUPPORTED))
+ gfp_mask = vmalloc_fix_flags(gfp_mask);
return __vmalloc_node_noprof(size, 1, gfp_mask, NUMA_NO_NODE,
__builtin_return_address(0));
}
@@ -4131,6 +4155,8 @@ EXPORT_SYMBOL(vmalloc_noprof);
*/
void *vmalloc_huge_node_noprof(unsigned long size, gfp_t gfp_mask, int node)
{
+ if (unlikely(gfp_mask & ~GFP_VMALLOC_SUPPORTED))
+ gfp_mask = vmalloc_fix_flags(gfp_mask);
return __vmalloc_node_range_noprof(size, 1, VMALLOC_START, VMALLOC_END,
gfp_mask, PAGE_KERNEL, VM_ALLOW_HUGE_VMAP,
node, __builtin_return_address(0));
--
2.51.1