linux-kernel - Re: [PATCH 03/13] sh/mm: Make pmd_t similar to pte

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Message-ID: <20221221135430.GA1510470@roeck-us.net>
Date:   Wed, 21 Dec 2022 05:54:30 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, willy@...radead.org, torvalds@...ux-foundation.org,
        akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, aarcange@...hat.com,
        kirill.shutemov@...ux.intel.com, jroedel@...e.de, ubizjak@...il.com
Subject: Re: [PATCH 03/13] sh/mm: Make pmd_t similar to pte_t

On Sat, Oct 22, 2022 at 01:14:06PM +0200, Peter Zijlstra wrote:
> Just like 64bit pte_t, have a low/high split in pmd_t.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

This patch causes a compile error when trying to build sh:defconfig.

In function 'follow_pmd_mask',
    inlined from 'follow_pud_mask' at mm/gup.c:735:9,
    inlined from 'follow_p4d_mask' at mm/gup.c:752:9,
    inlined from 'follow_page_mask' at mm/gup.c:809:9:
include/linux/compiler_types.h:358:45: error: call to '__compiletime_assert_263' declared with attribute error: Unsupported access size for {READ,WRITE}_ONCE().
...
mm/gup.c:661:18: note: in expansion of macro 'READ_ONCE'
  661 |         pmdval = READ_ONCE(*pmd);

> ---
>  arch/sh/include/asm/pgtable-3level.h |   10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> --- a/arch/sh/include/asm/pgtable-3level.h
> +++ b/arch/sh/include/asm/pgtable-3level.h
> @@ -28,9 +28,15 @@
>  #define pmd_ERROR(e) \
>  	printk("%s:%d: bad pmd %016llx.\n", __FILE__, __LINE__, pmd_val(e))
>  
> -typedef struct { unsigned long long pmd; } pmd_t;
> +typedef struct {

Was this supposed to be "union" ?

Guenter

> +	struct {
> +		unsigned long pmd_low;
> +		unsigned long pmd_high;
> +	};
> +	unsigned long long pmd;
> +} pmd_t;
>  #define pmd_val(x)	((x).pmd)
> -#define __pmd(x)	((pmd_t) { (x) } )
> +#define __pmd(x)	((pmd_t) { .pmd = (x) } )
>  
>  static inline pmd_t *pud_pgtable(pud_t pud)
>  {
> 
>