tpm: use GFP_KERNEL instead of GFP_HIGHMEM for tpm_buf

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.
Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>

drivers/char/tpm/tpm.h

@@ -282,7 +282,6 @@ enum tpm_buf_flags {
 };
 
 struct tpm_buf {
-	struct page *data_page;
 	unsigned int flags;
 	u8 *data;
 };
@@ -298,20 +297,18 @@ 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((unsigned long)buf->data);
 }
 
 static inline u32 tpm_buf_length(struct tpm_buf *buf)