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Date:   Wed, 27 Jan 2021 18:43:20 +0000
From:   Will Deacon <will@kernel.org>
To:     Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
Cc:     zohar@linux.ibm.com, bauerman@linux.ibm.com, robh@kernel.org,
        takahiro.akashi@linaro.org, gregkh@linuxfoundation.org,
        catalin.marinas@arm.com, mpe@ellerman.id.au, james.morse@arm.com,
        sashal@kernel.org, benh@kernel.crashing.org, paulus@samba.org,
        frowand.list@gmail.com, vincenzo.frascino@arm.com,
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        prsriva@linux.microsoft.com, balajib@linux.microsoft.com,
        linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v15 09/10] arm64: Call kmalloc() to allocate DTB buffer
Message-ID: <20210127184319.GA676@willie-the-truck>
References: <20210115173017.30617-1-nramas@linux.microsoft.com>
 <20210115173017.30617-10-nramas@linux.microsoft.com>
 <20210127165208.GA358@willie-the-truck>
 <d3330793-6054-6e59-b727-44bf8e5653cd@linux.microsoft.com>
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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@linux.microsoft.com>
> > > Signed-off-by: Prakhar Srivastava <prsriva@linux.microsoft.com>
> > > Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.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