| Message ID | 20240917073117.1531207-2-anshuman.khandual@arm.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm: Use pxdp_get() for accessing page table entries | expand |
On 17/09/2024 08:31, Anshuman Khandual wrote: > This changes platform's pmd_val() to access the pmd_t element directly like > other architectures rather than current pointer address based dereferencing > that prevents transition into pmdp_get(). > > Cc: Geert Uytterhoeven <geert@linux-m68k.org> > Cc: Guo Ren <guoren@kernel.org> > Cc: Arnd Bergmann <arnd@arndb.de> > Cc: linux-m68k@lists.linux-m68k.org > Cc: linux-kernel@vger.kernel.org > Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com> I know very little about m68k, but for what it's worth: Reviewed-by: Ryan Roberts <ryan.roberts@arm.com> > --- > arch/m68k/include/asm/page.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/m68k/include/asm/page.h b/arch/m68k/include/asm/page.h > index 8cfb84b49975..be3f2c2a656c 100644 > --- a/arch/m68k/include/asm/page.h > +++ b/arch/m68k/include/asm/page.h > @@ -19,7 +19,7 @@ > */ > #if !defined(CONFIG_MMU) || CONFIG_PGTABLE_LEVELS == 3 > typedef struct { unsigned long pmd; } pmd_t; > -#define pmd_val(x) ((&x)->pmd) > +#define pmd_val(x) ((x).pmd) > #define __pmd(x) ((pmd_t) { (x) } ) > #endif >
On 17.09.24 09:31, Anshuman Khandual wrote: > This changes platform's pmd_val() to access the pmd_t element directly like > other architectures rather than current pointer address based dereferencing > that prevents transition into pmdp_get(). > > Cc: Geert Uytterhoeven <geert@linux-m68k.org> > Cc: Guo Ren <guoren@kernel.org> > Cc: Arnd Bergmann <arnd@arndb.de> > Cc: linux-m68k@lists.linux-m68k.org > Cc: linux-kernel@vger.kernel.org > Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com> > --- > arch/m68k/include/asm/page.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/m68k/include/asm/page.h b/arch/m68k/include/asm/page.h > index 8cfb84b49975..be3f2c2a656c 100644 > --- a/arch/m68k/include/asm/page.h > +++ b/arch/m68k/include/asm/page.h > @@ -19,7 +19,7 @@ > */ > #if !defined(CONFIG_MMU) || CONFIG_PGTABLE_LEVELS == 3 > typedef struct { unsigned long pmd; } pmd_t; > -#define pmd_val(x) ((&x)->pmd) > +#define pmd_val(x) ((x).pmd) > #define __pmd(x) ((pmd_t) { (x) } ) > #endif > Trying to understand what's happening here, I stumbled over commit ef22d8abd876e805b604e8f655127de2beee2869 Author: Peter Zijlstra <peterz@infradead.org> Date: Fri Jan 31 13:45:36 2020 +0100 m68k: mm: Restructure Motorola MMU page-table layout The Motorola 68xxx MMUs, 040 (and later) have a fixed 7,7,{5,6} page-table setup, where the last depends on the page-size selected (8k vs 4k resp.), and head.S selects 4K pages. For 030 (and earlier) we explicitly program 7,7,6 and 4K pages in %tc. However, the current code implements this mightily weird. What it does is group 16 of those (6 bit) pte tables into one 4k page to not waste space. The down-side is that that forces pmd_t to be a 16-tuple pointing to consecutive pte tables. This breaks the generic code which assumes READ_ONCE(*pmd) will be word sized. Where we did #if !defined(CONFIG_MMU) || CONFIG_PGTABLE_LEVELS == 3 -typedef struct { unsigned long pmd[16]; } pmd_t; -#define pmd_val(x) ((&x)->pmd[0]) -#define __pmd(x) ((pmd_t) { { (x) }, }) +typedef struct { unsigned long pmd; } pmd_t; +#define pmd_val(x) ((&x)->pmd) +#define __pmd(x) ((pmd_t) { (x) } ) #endif So I assume this should be fine Acked-by: David Hildenbrand <david@redhat.com>
On 17/09/2024 11:20, David Hildenbrand wrote: > On 17.09.24 09:31, Anshuman Khandual wrote: >> This changes platform's pmd_val() to access the pmd_t element directly like >> other architectures rather than current pointer address based dereferencing >> that prevents transition into pmdp_get(). >> >> Cc: Geert Uytterhoeven <geert@linux-m68k.org> >> Cc: Guo Ren <guoren@kernel.org> >> Cc: Arnd Bergmann <arnd@arndb.de> >> Cc: linux-m68k@lists.linux-m68k.org >> Cc: linux-kernel@vger.kernel.org >> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com> >> --- >> arch/m68k/include/asm/page.h | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/arch/m68k/include/asm/page.h b/arch/m68k/include/asm/page.h >> index 8cfb84b49975..be3f2c2a656c 100644 >> --- a/arch/m68k/include/asm/page.h >> +++ b/arch/m68k/include/asm/page.h >> @@ -19,7 +19,7 @@ >> */ >> #if !defined(CONFIG_MMU) || CONFIG_PGTABLE_LEVELS == 3 >> typedef struct { unsigned long pmd; } pmd_t; >> -#define pmd_val(x) ((&x)->pmd) >> +#define pmd_val(x) ((x).pmd) >> #define __pmd(x) ((pmd_t) { (x) } ) >> #endif >> > > Trying to understand what's happening here, I stumbled over > > commit ef22d8abd876e805b604e8f655127de2beee2869 > Author: Peter Zijlstra <peterz@infradead.org> > Date: Fri Jan 31 13:45:36 2020 +0100 > > m68k: mm: Restructure Motorola MMU page-table layout > The Motorola 68xxx MMUs, 040 (and later) have a fixed 7,7,{5,6} > page-table setup, where the last depends on the page-size selected (8k > vs 4k resp.), and head.S selects 4K pages. For 030 (and earlier) we > explicitly program 7,7,6 and 4K pages in %tc. > However, the current code implements this mightily weird. What it does > is group 16 of those (6 bit) pte tables into one 4k page to not waste > space. The down-side is that that forces pmd_t to be a 16-tuple > pointing to consecutive pte tables. > This breaks the generic code which assumes READ_ONCE(*pmd) will be > word sized. > > Where we did > > #if !defined(CONFIG_MMU) || CONFIG_PGTABLE_LEVELS == 3 > -typedef struct { unsigned long pmd[16]; } pmd_t; > -#define pmd_val(x) ((&x)->pmd[0]) > -#define __pmd(x) ((pmd_t) { { (x) }, }) > +typedef struct { unsigned long pmd; } pmd_t; > +#define pmd_val(x) ((&x)->pmd) > +#define __pmd(x) ((pmd_t) { (x) } ) > #endif > > So I assume this should be fine I think you're implying that taking the address then using arrow operator was needed when pmd was an array? I don't really understand that if so? Surely: ((x).pmd[0]) would have worked too? I traced back further, and a version of that macro exists with the "address of" and arrow operator since the beginning of (git) time. > > Acked-by: David Hildenbrand <david@redhat.com> >
>> #if !defined(CONFIG_MMU) || CONFIG_PGTABLE_LEVELS == 3 >> -typedef struct { unsigned long pmd[16]; } pmd_t; >> -#define pmd_val(x) ((&x)->pmd[0]) >> -#define __pmd(x) ((pmd_t) { { (x) }, }) >> +typedef struct { unsigned long pmd; } pmd_t; >> +#define pmd_val(x) ((&x)->pmd) >> +#define __pmd(x) ((pmd_t) { (x) } ) >> #endif >> >> So I assume this should be fine > > I think you're implying that taking the address then using arrow operator was > needed when pmd was an array? I don't really understand that if so? Surely: > > ((x).pmd[0]) > > would have worked too? I think your right, I guess one suspects that there is more magic to it than there actually is ... :)
diff --git a/arch/m68k/include/asm/page.h b/arch/m68k/include/asm/page.h index 8cfb84b49975..be3f2c2a656c 100644 --- a/arch/m68k/include/asm/page.h +++ b/arch/m68k/include/asm/page.h @@ -19,7 +19,7 @@ */ #if !defined(CONFIG_MMU) || CONFIG_PGTABLE_LEVELS == 3 typedef struct { unsigned long pmd; } pmd_t; -#define pmd_val(x) ((&x)->pmd) +#define pmd_val(x) ((x).pmd) #define __pmd(x) ((pmd_t) { (x) } ) #endif
This changes platform's pmd_val() to access the pmd_t element directly like other architectures rather than current pointer address based dereferencing that prevents transition into pmdp_get(). Cc: Geert Uytterhoeven <geert@linux-m68k.org> Cc: Guo Ren <guoren@kernel.org> Cc: Arnd Bergmann <arnd@arndb.de> Cc: linux-m68k@lists.linux-m68k.org Cc: linux-kernel@vger.kernel.org Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com> --- arch/m68k/include/asm/page.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)