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

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Date:   Mon, 14 Oct 2019 12:35:40 -0700
From:   James Bottomley <James.Bottomley@...senPartnership.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.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 Mon, 2019-10-14 at 22:32 +0300, Jarkko Sakkinen wrote:
> 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.c
> > om>
> 
> 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.

I don't really mind either way.  The function of the fixes tag isn't to
say there was a fatal bug it's to say if you think you're fixing
something where was the origin of the problem, however minor the
problem is.

I do agree that Sasha's autosel stuff does seem to be triggering off
Fixes and we don't want to see hundreds of autosel patches trying to
apply this to older trees, so removing the fixes tag to avoid this is
fine with me.

James