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

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Date:   Thu, 03 Oct 2019 17:25:16 -0700
From:   James Bottomley <jejb@...ux.ibm.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        linux-integrity@...r.kernel.org
Cc:     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, 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)