linux-kernel - Re: [PATCH] tpm: Detach page allocation from tpm

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Message-ID: <1569420226.3642.24.camel@HansenPartnership.com>
Date:   Wed, 25 Sep 2019 10:03:46 -0400
From:   James Bottomley <James.Bottomley@...senPartnership.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        linux-integrity@...r.kernel.org
Cc:     Mimi Zohar <zohar@...ux.ibm.com>,
        Jerry Snitselaar <jsnitsel@...hat.com>,
        Sumit Garg <sumit.garg@...aro.org>,
        Stefan Berger <stefanb@...ux.vnet.ibm.com>,
        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] tpm: Detach page allocation from tpm_buf

On Wed, 2019-09-25 at 16:48 +0300, Jarkko Sakkinen wrote:
[...]
> +	data_page = alloc_page(GFP_HIGHUSER);
> +	if (!data_page)
> +		return -ENOMEM;
> +
> +	data_ptr = kmap(data_page);

I don't think this is such a good idea.  On 64 bit it's no different
from GFP_KERNEL and on 32 bit where we do have highmem, kmap space is
at a premium, so doing a highmem allocation + kmap is more wasteful of
resources than simply doing GFP_KERNEL.  In general, you should only do
GFP_HIGHMEM if the page is going to be mostly used by userspace, which
really isn't the case here.

James