Re: [PATCH v15 09/10] arm64: Call kmalloc() to allocate DTB buffer

[Lakshmi Ramasubramanian]

On 1/27/21 8:52 AM, Will Deacon wrote:

Hi Will,

> On Fri, Jan 15, 2021 at 09:30:16AM -0800, Lakshmi Ramasubramanian wrote:
> > create_dtb() function allocates kernel virtual memory for
> > the device tree blob (DTB).  This is not consistent with other
> > architectures, such as powerpc, which calls kmalloc() for allocating
> > memory for the DTB.
> >
> > Call kmalloc() to allocate memory for the DTB, and kfree() to free
> > the allocated memory.
> >
> > Co-developed-by: Prakhar Srivastava <prsriva@xxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Prakhar Srivastava <prsriva@xxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Lakshmi Ramasubramanian <nramas@xxxxxxxxxxxxxxxxxxx>
> > ---
> >   arch/arm64/kernel/machine_kexec_file.c | 12 +++++++-----
> >   1 file changed, 7 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c
> > index 7de9c47dee7c..51c40143d6fa 100644
> > --- a/arch/arm64/kernel/machine_kexec_file.c
> > +++ b/arch/arm64/kernel/machine_kexec_file.c
> > @@ -29,7 +29,7 @@ const struct kexec_file_ops * const kexec_file_loaders[] = {
> >   
> >   int arch_kimage_file_post_load_cleanup(struct kimage *image)
> >   {
> > -	vfree(image->arch.dtb);
> > +	kfree(image->arch.dtb);
> >   	image->arch.dtb = NULL;
> >   
> >   	vfree(image->arch.elf_headers);
> > @@ -59,19 +59,21 @@ static int create_dtb(struct kimage *image,
> >   			+ cmdline_len + DTB_EXTRA_SPACE;
> >   
> >   	for (;;) {
> > -		buf = vmalloc(buf_size);
> > +		buf = kmalloc(buf_size, GFP_KERNEL);
>
> Is there a functional need for this patch? I build the 'dtbs' target just
> now and sdm845-db845c.dtb is approaching 100K, which feels quite large
> for kmalloc().

Changing the allocation from vmalloc() to kmalloc() would help us 
further consolidate the DTB setup code for powerpc and arm64.

thanks,
 -lakshmi