linux-kernel - Re: [PATCH v2] tpm: use GFP kernel for tpm

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Message-ID: <20191014193224.GF15552@linux.intel.com>
Date:   Mon, 14 Oct 2019 22:32:24 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     James Bottomley <James.Bottomley@...senPartnership.com>
Cc:     linux-integrity@...r.kernel.org,
        open list <linux-kernel@...r.kernel.org>,
        Jerry Snitselaar <jsnitsel@...hat.com>
Subject: Re: [PATCH v2] tpm: use GFP kernel for tpm_buf allocations

On Fri, Oct 11, 2019 at 09:02:59AM -0700, James Bottomley wrote:
> The current code uses GFP_HIGHMEM, which is wrong because GFP_HIGHMEM
> (on 32 bit systems) is memory ordinarily inaccessible to the kernel
> and should only be used for allocations affecting userspace.  In order
> to make highmem visible to the kernel on 32 bit it has to be kmapped,
> which consumes valuable entries in the kmap region.  Since the tpm_buf
> is only ever used in the kernel, switch to using a GFP_KERNEL
> allocation so as not to waste kmap space on 32 bits.
> 
> Fixes: a74f8b36352e (tpm: introduce tpm_buf)
> Reviewed-by: Jerry Snitselaar <jsnitsel@...hat.com>
> Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
> Signed-off-by: James Bottomley <James.Bottomley@...senPartnership.com>

I'll apply this without a fixes tag as there is no failing system.
Agree that it was not the best design decision to use GFP_HIGHMEM.

/Jarkko