linux-kernel - Re: [PATCH v3 1/4] mm/vmalloc: warn on invalid vmalloc gfp flags

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Message-ID: <aRw9rJ5hx2Wrtq_Y@pc636>
Date: Tue, 18 Nov 2025 10:34:36 +0100
From: Uladzislau Rezki <urezki@...il.com>
To: "Vishal Moola (Oracle)" <vishal.moola@...il.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, bpf@...r.kernel.org,
	Uladzislau Rezki <urezki@...il.com>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v3 1/4] mm/vmalloc: warn on invalid vmalloc gfp flags

On Mon, Nov 17, 2025 at 09:35:27AM -0800, Vishal Moola (Oracle) wrote:
> 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@...radead.org>
> Signed-off-by: Vishal Moola (Oracle) <vishal.moola@...il.com>
> Reviewed-by: Christoph Hellwig <hch@....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
> 
Reviewed-by: "Uladzislau Rezki (Sony)" <urezki@...il.com>

--
Uladzislau Rezki