linux-kernel - [PATCH v3 0/4] make vmalloc gfp flags usage more apparent

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Message-ID: <20251117173530.43293-1-vishal.moola@gmail.com>
Date: Mon, 17 Nov 2025 09:35:26 -0800
From: "Vishal Moola (Oracle)" <vishal.moola@...il.com>
To: linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	bpf@...r.kernel.org
Cc: Uladzislau Rezki <urezki@...il.com>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Vishal Moola (Oracle)" <vishal.moola@...il.com>
Subject: [PATCH v3 0/4] make vmalloc gfp flags usage more apparent

We should do a better job at enforcing gfp flags for vmalloc. Right now, we
have a kernel-doc for __vmalloc_node_range(), and hope callers pass in
supported flags. If a caller were to pass in an unsupported flag, we may
BUG, silently clear it, or completely ignore it.

If we are more proactive about enforcing gfp flags, we can making sure
callers know when they may be asking for unsupported behavior.

This patchset lets vmalloc control the incoming gfp flags, and cleans up
some hard to read gfp code.

---
Linked rfc [1] and rfc v2[2] for convenience.

Patch v2 -> v3:
  Only changes the whitelist mask and comment in patch 1:
  - Replace __GFP_HARDWALL with GFP_USER
  - Add GFP_KERNEL_ACCOUNT[4]
  - Add GFP_NOFS and GFP_NOIO just so all supported flags are explicitly
    listed in the mask.

v2:
  - Add __GFP_HARDWALL[3] for bpf and drm users.
  - cc BPF mailing list

RFC -> PATCH:
  - Collected review tags (Patches 1 & 4)
  - Add unlikely keyword to help the compiler
  - Replace pr_warn() with WARN(1)

RFC v2:
  - Whitelist supported gfp flags instead of blacklisting the unsupported
  - Move the flags check up to the only exported functions that accept
    flags:
	__vmalloc_noprof() and vmalloc_huge_node_prof()

[1] https://lore.kernel.org/linux-mm/20251030164330.44995-1-vishal.moola@gmail.com/
[2] https://lore.kernel.org/linux-mm/20251103190429.104747-1-vishal.moola@gmail.com/
[3] https://lore.kernel.org/linux-mm/20251110160457.61791-1-vishal.moola@gmail.com/T/#me8b548520ce9c81a5099c00abe53dd248c16eae7
[4] https://lore.kernel.org/linux-mm/69158bb1.a70a0220.3124cb.001e.GAE@google.com/

Vishal Moola (Oracle) (4):
  mm/vmalloc: warn on invalid vmalloc gfp flags
  mm/vmalloc: Add a helper to optimize vmalloc allocation gfps
  mm/vmalloc: cleanup large_gfp in vm_area_alloc_pages()
  mm/vmalloc: cleanup gfp flag use in new_vmap_block()

 mm/vmalloc.c | 50 ++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 42 insertions(+), 8 deletions(-)

-- 
2.51.1