Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH] tpm: Detach page allocation from tpm_buf
From:   Mimi Zohar <zohar@linux.ibm.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
        James Bottomley <James.Bottomley@HansenPartnership.com>
Cc:     linux-integrity@vger.kernel.org,
        Jerry Snitselaar <jsnitsel@redhat.com>,
        Sumit Garg <sumit.garg@linaro.org>,
        Stefan Berger <stefanb@linux.vnet.ibm.com>,
        Peter Huewe <peterhuewe@gmx.de>,
        Jason Gunthorpe <jgg@ziepe.ca>, Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        open list <linux-kernel@vger.kernel.org>
Date:   Wed, 02 Oct 2019 08:41:45 -0400
In-Reply-To: <20190927130657.GA5556@linux.intel.com>
References: <20190925134842.19305-1-jarkko.sakkinen@linux.intel.com>
         <1569420226.3642.24.camel@HansenPartnership.com>
         <20190927130657.GA5556@linux.intel.com>
Content-Type: text/plain; charset="UTF-8"
Mime-Version: 1.0
Content-Transfer-Encoding: 8bit
Message-Id: <1570020105.4999.106.camel@linux.ibm.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Fri, 2019-09-27 at 16:06 +0300, Jarkko Sakkinen wrote:
> On Wed, Sep 25, 2019 at 10:03:46AM -0400, James Bottomley wrote:
> > 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.
> 
> Changing that in this commit would be wrong even if you are right.
> After this commit has been applied it is somewhat easier to make
> best choices for allocation in each call site (probably most will
> end up using stack).

Agreed, but it could be a separate patch, prior to this one.  Why
duplicate the problem all over only to change it later?

Mimi