From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Hildenbrand Date: Thu, 08 Dec 2022 08:55:49 +0000 Subject: Re: [PATCH mm-unstable RFC 17/26] powerpc/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE on 32bit book3s Message-Id: List-Id: References: <20221206144730.163732-1-david@redhat.com> <20221206144730.163732-18-david@redhat.com> <8be167b6-3836-25c3-9f69-b8b3916ee5b4@csgroup.eu> <0b5b1303-8bcb-c19d-5f63-0e4a3517fea5@redhat.com> In-Reply-To: <0b5b1303-8bcb-c19d-5f63-0e4a3517fea5@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit To: Christophe Leroy , "linux-kernel@vger.kernel.org" Cc: 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" , "linuxppc-dev@lists.ozlabs.org" , "linux-riscv@lists.infradead.org" , "linux-s390@vger.kernel.org" , "linux-sh@vger.kernel.org" , "sparclinux@vger.kernel.org" , "linux-um@lists.infradead.org" , "linux-xtensa@linux-xtensa.org" , Michael Ellerman , Nicholas Piggin On 08.12.22 09:52, David Hildenbrand wrote: > On 07.12.22 14:55, Christophe Leroy wrote: >> >> >> Le 06/12/2022 à 15:47, David Hildenbrand a écrit : >>> We already implemented support for 64bit book3s in commit bff9beaa2e80 >>> ("powerpc/pgtable: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE for book3s") >>> >>> Let's support __HAVE_ARCH_PTE_SWP_EXCLUSIVE also in 32bit by reusing yet >>> unused LSB 2 / MSB 29. There seems to be no real reason why that bit cannot >>> be used, and reusing it avoids having to steal one bit from the swap >>> offset. >>> >>> While at it, mask the type in __swp_entry(). >>> >>> Cc: Michael Ellerman >>> Cc: Nicholas Piggin >>> Cc: Christophe Leroy >>> Signed-off-by: David Hildenbrand >>> --- >>> arch/powerpc/include/asm/book3s/32/pgtable.h | 38 +++++++++++++++++--- >>> 1 file changed, 33 insertions(+), 5 deletions(-) >>> >>> diff --git a/arch/powerpc/include/asm/book3s/32/pgtable.h b/arch/powerpc/include/asm/book3s/32/pgtable.h >>> index 75823f39e042..8107835b38c1 100644 >>> --- a/arch/powerpc/include/asm/book3s/32/pgtable.h >>> +++ b/arch/powerpc/include/asm/book3s/32/pgtable.h >>> @@ -42,6 +42,9 @@ >>> #define _PMD_PRESENT_MASK (PAGE_MASK) >>> #define _PMD_BAD (~PAGE_MASK) >>> >>> +/* We borrow the _PAGE_USER bit to store the exclusive marker in swap PTEs. */ >>> +#define _PAGE_SWP_EXCLUSIVE _PAGE_USER >>> + >>> /* And here we include common definitions */ >>> >>> #define _PAGE_KERNEL_RO 0 >>> @@ -363,17 +366,42 @@ static inline void __ptep_set_access_flags(struct vm_area_struct *vma, >>> #define pmd_page(pmd) pfn_to_page(pmd_pfn(pmd)) >>> >>> /* >>> - * Encode and decode a swap entry. >>> - * Note that the bits we use in a PTE for representing a swap entry >>> - * must not include the _PAGE_PRESENT bit or the _PAGE_HASHPTE bit (if used). >>> - * -- paulus >>> + * Encode/decode swap entries and swap PTEs. Swap PTEs are all PTEs that >>> + * are !pte_none() && !pte_present(). >>> + * >>> + * Format of swap PTEs (32bit PTEs): >>> + * >>> + * 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 >>> + * 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 >>> + * E H P <- type --> <----------------- offset ------------------> >> >> That's in reversed order. _PAGE_HASHPTE is bit 30 and should be on the >> right hand side. Etc ... > > Ugh, messed it up while converting back and forth between LSB 0 and MSB 0. > > /* > * Format of swap PTEs (32bit PTEs): > * > * 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 > * 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 > * <----------------- offset ------------------> <- type --> E H P > > Still wrong, the type is only 5 bits: + * Format of swap PTEs (32bit PTEs): + * + * 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 + * 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + * <----------------- offset --------------------> < type -> E H P + * -- Thanks, David / dhildenb