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

Vishal Moola (Oracle) posted 4 patches 2 weeks ago
There is a newer version of this series
[PATCH v3 1/4] mm/vmalloc: warn on invalid vmalloc gfp flags
Posted by Vishal Moola (Oracle) 2 weeks ago 
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
Re: [PATCH v3 1/4] mm/vmalloc: warn on invalid vmalloc gfp flags
Posted by Nathan Chancellor 1 week, 6 days ago 
Hi Vishal,

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@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;
> +}

I am seeing this warning trigger when starting a VM on one of my arm64
boxes.

  [ 6345.145795] ------------[ cut here ]------------
  [ 6345.145803] Unexpected gfp: 0x2 (__GFP_HIGHMEM). Fixing up to gfp: 0x400dc0 (GFP_KERNEL_ACCOUNT|__GFP_ZERO). Fix your code!
  [ 6345.145819] WARNING: mm/vmalloc.c:3940 at vmalloc_fix_flags+0x60/0x90, CPU#32: qemu-system-aar/4325
  [ 6345.176990] Modules linked in: ...
  [ 6345.254421] CPU: 32 UID: 1000 PID: 4325 Comm: qemu-system-aar Not tainted 6.18.0-rc6-next-20251118-00002-g2331e73a4769 #1 PREEMPT(voluntary)
  [ 6345.267101] Hardware name: To be filled by O.E.M Ampere Altra Developer Platform/Ampere Altra Developer Platform, BIOS TianoCore 2.10.100.02 (SYS: 2.10.20
  [ 6345.280907] pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
  [ 6345.287856] pc : vmalloc_fix_flags+0x60/0x90
  [ 6345.292115] lr : vmalloc_fix_flags+0x58/0x90
  [ 6345.296374] sp : ffff80008d5b3a10
  [ 6345.299676] x29: ffff80008d5b3a20 x28: ffff07ff8a148000 x27: 0000000000000000
  [ 6345.306800] x26: 0000000000000000 x25: 0000000000000000 x24: 0000000000000000
  [ 6345.313923] x23: 000000000000000b x22: 000000000000ae01 x21: 0000000000000028
  [ 6345.321047] x20: ffffc682ea643fbc x19: 0000000000001040 x18: ffff800083465050
  [ 6345.328170] x17: 00000000d949c370 x16: 00000000d949c370 x15: 0000000000000004
  [ 6345.335294] x14: 0000000000000002 x13: 0000000000000002 x12: 0000000000000000
  [ 6345.342417] x11: 0000000000000001 x10: ffffc682ec577744 x9 : bf6a46a6bf3b7900
  [ 6345.349541] x8 : bf6a46a6bf3b7900 x7 : 65646f632072756f x6 : 7920786946202e29
  [ 6345.356664] x5 : ffff081f6fcdc678 x4 : 0000000000000000 x3 : ffff80008d5b3688
  [ 6345.363788] x2 : 0000000000000021 x1 : 0000000000000000 x0 : 000000000000006f
  [ 6345.370911] Call trace:
  [ 6345.373346]  vmalloc_fix_flags+0x60/0x90 (P)
  [ 6345.377606]  __vmalloc_noprof+0xa0/0xb0
  [ 6345.381431]  kvm_arch_alloc_vm+0x64/0x70
  [ 6345.385344]  kvm_dev_ioctl+0x9c/0x58c
  [ 6345.388997]  __arm64_sys_ioctl+0xb0/0x100
  [ 6345.392995]  invoke_syscall+0x84/0xf4
  [ 6345.396648]  el0_svc_common.llvm.4390888008543260363+0x90/0xf4
  [ 6345.402469]  do_el0_svc+0x2c/0x3c
  [ 6345.405773]  el0_svc+0x54/0x2a8
  [ 6345.408905]  el0t_64_sync_handler+0x88/0x134
  [ 6345.413164]  el0t_64_sync+0x1b8/0x1bc
  [ 6345.416815] ---[ end trace 0000000000000000 ]---

where kvm_arch_alloc_vm() from arch/arm64/kvm/arm.c is

  struct kvm *kvm_arch_alloc_vm(void)
  {
      size_t sz = sizeof(struct kvm);

      if (!has_vhe())
          return kzalloc(sz, GFP_KERNEL_ACCOUNT);

      return __vmalloc(sz, GFP_KERNEL_ACCOUNT | __GFP_HIGHMEM | __GFP_ZERO);
  }

Should __GFP_HIGHMEM be dropped from the call to __vmalloc? It looks
like it was added by commit 115bae923ac8 ("KVM: arm64: Add memcg
accounting to KVM allocations") back in 5.16.

Cheers,
Nathan
Re: [PATCH v3 1/4] mm/vmalloc: warn on invalid vmalloc gfp flags
Posted by Christoph Hellwig 1 week, 5 days ago 
On Tue, Nov 18, 2025 at 03:44:48PM -0700, Nathan Chancellor wrote:
> where kvm_arch_alloc_vm() from arch/arm64/kvm/arm.c is
> 
>   struct kvm *kvm_arch_alloc_vm(void)
>   {
>       size_t sz = sizeof(struct kvm);
> 
>       if (!has_vhe())
>           return kzalloc(sz, GFP_KERNEL_ACCOUNT);
> 
>       return __vmalloc(sz, GFP_KERNEL_ACCOUNT | __GFP_HIGHMEM | __GFP_ZERO);
>   }
> 
> Should __GFP_HIGHMEM be dropped from the call to __vmalloc?

Yes.  vmalloc uses highmem internally where useful (on arm64 it won't be
useful of course).
Re: [PATCH v3 1/4] mm/vmalloc: warn on invalid vmalloc gfp flags
Posted by Oliver Upton 1 week, 6 days ago 
Hi Nathan,

Thanks for reporting this.

On Tue, Nov 18, 2025 at 03:44:48PM -0700, Nathan Chancellor wrote:
> where kvm_arch_alloc_vm() from arch/arm64/kvm/arm.c is
> 
>   struct kvm *kvm_arch_alloc_vm(void)
>   {
>       size_t sz = sizeof(struct kvm);
> 
>       if (!has_vhe())
>           return kzalloc(sz, GFP_KERNEL_ACCOUNT);
> 
>       return __vmalloc(sz, GFP_KERNEL_ACCOUNT | __GFP_HIGHMEM | __GFP_ZERO);
>   }
> 
> Should __GFP_HIGHMEM be dropped from the call to __vmalloc? It looks
> like it was added by commit 115bae923ac8 ("KVM: arm64: Add memcg
> accounting to KVM allocations") back in 5.16.

Yep. May as well switch to kvzalloc() while we're at it.

Thanks,
Oliver
Re: [PATCH v3 1/4] mm/vmalloc: warn on invalid vmalloc gfp flags
Posted by Uladzislau Rezki 1 week, 6 days ago 
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@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
> 
Reviewed-by: "Uladzislau Rezki (Sony)" <urezki@gmail.com>

--
Uladzislau Rezki

Patchew 2.1-devel-b67e4c2

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