linux-kernel - Re: [PATCH] drm/panthor: Fix potential memleak of vma structure

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Message-ID: <6549faee-1633-427a-b7e8-3722808976f2@arm.com>
Date: Mon, 20 Oct 2025 10:50:19 +0100
From: Akash Goel <akash.goel@....com>
To: Boris Brezillon <boris.brezillon@...labora.com>
Cc: liviu.dudau@....com, steven.price@....com,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 maarten.lankhorst@...ux.intel.com, mripard@...nel.org, tzimmermann@...e.de,
 airlied@...il.com, daniel@...ll.ch, nd@....com
Subject: Re: [PATCH] drm/panthor: Fix potential memleak of vma structure



On 10/20/25 10:30, Boris Brezillon wrote:
> On Mon, 20 Oct 2025 09:59:14 +0100
> Akash Goel <akash.goel@....com> wrote:
> 
>> This commit addresses a memleak issue of panthor_vma (or drm_gpuva)
>> structure in Panthor driver, that can happen if the GPU page table
>> update operation to map the pages fail.
>> The issue is very unlikely to occur in practice.
>>
>> Fixes: 647810ec2476 ("drm/panthor: Add the MMU/VM logical block")
>> Signed-off-by: Akash Goel <akash.goel@....com>
>> ---
>>   drivers/gpu/drm/panthor/panthor_mmu.c | 4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
>> index 6dec4354e378..34a86f7b58d9 100644
>> --- a/drivers/gpu/drm/panthor/panthor_mmu.c
>> +++ b/drivers/gpu/drm/panthor/panthor_mmu.c
>> @@ -2081,8 +2081,10 @@ static int panthor_gpuva_sm_step_map(struct drm_gpuva_op *op, void *priv)
>>   	ret = panthor_vm_map_pages(vm, op->map.va.addr, flags_to_prot(vma->flags),
>>   				   op_ctx->map.sgt, op->map.gem.offset,
>>   				   op->map.va.range);
>> -	if (ret)
>> +	if (ret) {
>> +		kfree(vma);
> 
> Calling kfree() in this context is probably fine, but I think I'd
> prefer if we were introducing a panthor_vm_op_ctx_return_vma() helper
> returning the vma to the preallocated array, and letting the deferred
> cleanup function free this up.


Thanks for the quick review.

So need to do like this, where we search for a NULL entry to store the 
VMA pointer to be returned ?

static void
panthor_vm_op_ctx_return_vma(struct panthor_vm_op_ctx *op_ctx,
			     struct panthor_vma *vma)
{
	for (u32 i = 0; i < ARRAY_SIZE(op_ctx->preallocated_vmas); i++) {
		if (!op_ctx->preallocated_vmas[i]) {
			op_ctx->preallocated_vmas[i] = vma;
			return;
		}
	}
}


Please let me know.

Best regards
Akash

> 
>>   		return ret;
>> +	}
>>   
>>   	/* Ref owned by the mapping now, clear the obj field so we don't release the
>>   	 * pinning/obj ref behind GPUVA's back.
>