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

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Date:   Sun, 6 Oct 2019 13:03:53 +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 Thu, Oct 03, 2019 at 05:25:16PM -0700, James Bottomley wrote:
> On Thu, 2019-10-03 at 21:51 +0300, Jarkko Sakkinen wrote:
> > Switch from GFP_HIGHUSER to GFP_KERNEL. On 32-bit platforms kmap()
> > space
> > could be unnecessarily wasted because of using GFP_HIGHUSER by taking
> > a
> > page of from the highmem.
> > 
> > Suggested-by: James Bottomley <jejb@...ux.ibm.com>
> > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
> > ---
> >  drivers/char/tpm/tpm.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
> > index a4f74dd02a35..d20745965350 100644
> > --- a/drivers/char/tpm/tpm.h
> > +++ b/drivers/char/tpm/tpm.h
> > @@ -297,7 +297,7 @@ static inline void tpm_buf_reset(struct tpm_buf
> > *buf, u16 tag, u32 ordinal)
> >  
> >  static inline int tpm_buf_init(struct tpm_buf *buf, u16 tag, u32
> > ordinal)
> >  {
> > -	buf->data_page = alloc_page(GFP_HIGHUSER);
> > +	buf->data_page = alloc_page(GFP_KERNEL);
> >  	if (!buf->data_page)
> >  		return -ENOMEM;
> 
> The kmap/kunmap needs removing as well, and now the data_page field
> isn't necessary, so it can go.  I think the result should be something
> like the below (uncompiled and untested).
> 
> James
> 
> ---
> 
> diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
> index a7fea3e0ca86..b4f1cbf344b6 100644
> --- a/drivers/char/tpm/tpm.h
> +++ b/drivers/char/tpm/tpm.h
> @@ -284,7 +284,6 @@ enum tpm_buf_flags {
>  };
>  
>  struct tpm_buf {
> -	struct page *data_page;
>  	unsigned int flags;
>  	u8 *data;
>  };
> @@ -300,20 +299,18 @@ static inline void tpm_buf_reset(struct tpm_buf *buf, u16 tag, u32 ordinal)
>  
>  static inline int tpm_buf_init(struct tpm_buf *buf, u16 tag, u32 ordinal)
>  {
> -	buf->data_page = alloc_page(GFP_HIGHUSER);
> -	if (!buf->data_page)
> +	buf->data = (u8 *)__get_free_page(GFP_KERNEL);
> +	if (!buf->data)
>  		return -ENOMEM;
>  
>  	buf->flags = 0;
> -	buf->data = kmap(buf->data_page);
>  	tpm_buf_reset(buf, tag, ordinal);
>  	return 0;
>  }
>  
>  static inline void tpm_buf_destroy(struct tpm_buf *buf)
>  {
> -	kunmap(buf->data_page);
> -	__free_page(buf->data_page);
> +	free_page(buf->data);
>  }
>  
>  static inline u32 tpm_buf_length(struct tpm_buf *buf)
> 
> 

Care to make this a proper patch? Much better idea to do it this
way, agreed.

/Jarkko