linux-kernel - Re: [PATCH v3 1/2] tpm: Use GFP_KERNEL for allocating struct tpm

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Message-ID: <20191008225202.GA12089@linux.intel.com>
Date:   Wed, 9 Oct 2019 01:52:02 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     James Bottomley <jejb@...ux.ibm.com>
Cc:     linux-integrity@...r.kernel.org, Peter Huewe <peterhuewe@....de>,
        Jason Gunthorpe <jgg@...pe.ca>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/2] tpm: Use GFP_KERNEL for allocating struct tpm_buf

On Mon, Oct 07, 2019 at 12:12:08PM -0700, James Bottomley wrote:
> From: James Bottomley <James.Bottomley@...senPartnership.com>
> Subject: [PATCH] tpm: use GFP kernel for tpm_buf allocations
> 
> 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)
> Signed-off-by: James Bottomley <James.Bottomley@...senPartnership.com>

Thanks a lot. Makes a lot more sense than the patch that I sent.

Reviewed-by:  Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>

/Jarkko