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

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Message-ID: <20210127184319.GA676@willie-the-truck>
Date:   Wed, 27 Jan 2021 18:43:20 +0000
From:   Will Deacon <will@...nel.org>
To:     Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
Cc:     zohar@...ux.ibm.com, bauerman@...ux.ibm.com, robh@...nel.org,
        takahiro.akashi@...aro.org, gregkh@...uxfoundation.org,
        catalin.marinas@....com, mpe@...erman.id.au, james.morse@....com,
        sashal@...nel.org, benh@...nel.crashing.org, paulus@...ba.org,
        frowand.list@...il.com, vincenzo.frascino@....com,
        mark.rutland@....com, dmitry.kasatkin@...il.com, jmorris@...ei.org,
        serge@...lyn.com, pasha.tatashin@...een.com, allison@...utok.net,
        masahiroy@...nel.org, bhsharma@...hat.com, mbrugger@...e.com,
        hsinyi@...omium.org, tao.li@...o.com, christophe.leroy@....fr,
        prsriva@...ux.microsoft.com, balajib@...ux.microsoft.com,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v15 09/10] arm64: Call kmalloc() to allocate DTB buffer

On Wed, Jan 27, 2021 at 09:59:38AM -0800, Lakshmi Ramasubramanian wrote:
> 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@...ux.microsoft.com>
> > > Signed-off-by: Prakhar Srivastava <prsriva@...ux.microsoft.com>
> > > Signed-off-by: Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
> > > ---
> > >   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.

Ok, but at the risk of allocation failure. Can powerpc use vmalloc()
instead?

Will