From mboxrd@z Thu Jan 1 00:00:00 1970 From: Geert Uytterhoeven Subject: Re: [PATCH mm-unstable v1 11/26] microblaze/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE Date: Sun, 26 Feb 2023 21:13:33 +0100 Message-ID: References: <20230113171026.582290-1-david@redhat.com> <20230113171026.582290-12-david@redhat.com> Mime-Version: 1.0 Return-path: In-Reply-To: <20230113171026.582290-12-david@redhat.com> List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, Andrew Morton , Hugh Dickins , John Hubbard , Jason Gunthorpe , Mike Rapoport , Yang Shi , Vlastimil Babka , Nadav Amit , Andrea Arcangeli , Peter Xu , linux-mm@kvack.org, x86@kernel.org, linux-alpha@vger.kernel.org, linux-snps-arc@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-csky@vger.kernel.org, linux-hexagon@vger.kernel.org, linux-ia64@vger.kernel.org, loongarch@lists.linux.dev, linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, openrisc@lists.librecores.org, linux-parisc@vger.kernel.org, linuxp Hi David, On Fri, Jan 13, 2023 at 6:16 PM David Hildenbrand wrote: > Let's support __HAVE_ARCH_PTE_SWP_EXCLUSIVE by stealing one bit > from the type. Generic MM currently only uses 5 bits for the type > (MAX_SWAPFILES_SHIFT), so the stolen bit is effectively unused. > > The shift by 2 when converting between PTE and arch-specific swap entry > makes the swap PTE layout a little bit harder to decipher. > > While at it, drop the comment from paulus---copy-and-paste leftover > from powerpc where we actually have _PAGE_HASHPTE---and mask the type in > __swp_entry_to_pte() as well. > > Cc: Michal Simek > Signed-off-by: David Hildenbrand Thanks for your patch, which is now commit b5c88f21531c3457 ("microblaze/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE") in > arch/m68k/include/asm/mcf_pgtable.h | 4 +-- What is this m68k change doing here? Sorry for not noticing this earlier. Furthermore, several things below look strange to me... > arch/microblaze/include/asm/pgtable.h | 45 +++++++++++++++++++++------ > 2 files changed, 37 insertions(+), 12 deletions(-) > > diff --git a/arch/m68k/include/asm/mcf_pgtable.h b/arch/m68k/include/asm/mcf_pgtable.h > index 3f8f4d0e66dd..e573d7b649f7 100644 > --- a/arch/m68k/include/asm/mcf_pgtable.h > +++ b/arch/m68k/include/asm/mcf_pgtable.h > @@ -46,8 +46,8 @@ > #define _CACHEMASK040 (~0x060) > #define _PAGE_GLOBAL040 0x400 /* 68040 global bit, used for kva descs */ > > -/* We borrow bit 7 to store the exclusive marker in swap PTEs. */ > -#define _PAGE_SWP_EXCLUSIVE 0x080 > +/* We borrow bit 24 to store the exclusive marker in swap PTEs. */ > +#define _PAGE_SWP_EXCLUSIVE CF_PAGE_NOCACHE CF_PAGE_NOCACHE is 0x80, so this is still bit 7, thus the new comment is wrong? > > /* > * Externally used page protection values. > diff --git a/arch/microblaze/include/asm/pgtable.h b/arch/microblaze/include/asm/pgtable.h > index 42f5988e998b..7e3de54bf426 100644 > --- a/arch/microblaze/include/asm/pgtable.h > +++ b/arch/microblaze/include/asm/pgtable.h > @@ -131,10 +131,10 @@ extern pte_t *va_to_pte(unsigned long address); > * of the 16 available. Bit 24-26 of the TLB are cleared in the TLB > * miss handler. Bit 27 is PAGE_USER, thus selecting the correct > * zone. > - * - PRESENT *must* be in the bottom two bits because swap cache > - * entries use the top 30 bits. Because 4xx doesn't support SMP > - * anyway, M is irrelevant so we borrow it for PAGE_PRESENT. Bit 30 > - * is cleared in the TLB miss handler before the TLB entry is loaded. > + * - PRESENT *must* be in the bottom two bits because swap PTEs use the top > + * 30 bits. Because 4xx doesn't support SMP anyway, M is irrelevant so we > + * borrow it for PAGE_PRESENT. Bit 30 is cleared in the TLB miss handler > + * before the TLB entry is loaded. So the PowerPC 4xx comment is still here? > * - All other bits of the PTE are loaded into TLBLO without > * * modification, leaving us only the bits 20, 21, 24, 25, 26, 30 for > * software PTE bits. We actually use bits 21, 24, 25, and > @@ -155,6 +155,9 @@ extern pte_t *va_to_pte(unsigned long address); > #define _PAGE_ACCESSED 0x400 /* software: R: page referenced */ > #define _PMD_PRESENT PAGE_MASK > > +/* We borrow bit 24 to store the exclusive marker in swap PTEs. */ > +#define _PAGE_SWP_EXCLUSIVE _PAGE_DIRTY _PAGE_DIRTY is 0x80, so this is also bit 7, thus the new comment is wrong? Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds