Re: [PATCH RFC 09/13] mm/powerpc: Redefine pXd_huge() with pXd_leaf()
From: Michael Ellerman <mpe@ellerman.id.au>
Date: 2024-03-06 12:57:01
Also in:
linux-arm-kernel, linux-mm, lkml, sparclinux
Subsystem:
linux for powerpc (32-bit and 64-bit), the rest · Maintainers:
Madhavan Srinivasan, Linus Torvalds
peterx@redhat.com writes:
From: Peter Xu <peterx@redhat.com> PowerPC book3s 4K mostly has the same definition on both, except pXd_huge() constantly returns 0 for hash MMUs. AFAICT that is fine to be removed, because pXd_huge() reflects a hugetlb entry, while it's own hugetlb pgtable lookup function (__find_linux_pte() shared by all powerpc code) already use pXd_leaf() irrelevant of the MMU type. It means pXd_leaf() should work all fine with hash MMU pgtables or something could already went wrong.
Yes I think that's correct.
4K Hash MMU doesn't support any hugepage size at PMD or PUD level (the
geometry is wrong), so pmd/pud_huge() were written with that in mind,
ie. they are hard coded to return false.
But it should be OK to use pmd/pud_leaf(), they will actually look for
_PAGE_PTE, but it should never be set for 4K Hash.
See eg. arch/powerpc/include/asm/book3s/64/hash-4k.h:
static inline pmd_t hash__pmd_mkhuge(pmd_t pmd)
{
BUG();
return pmd;
}
quoted hunk ↗ jump to hunk
The goal should be that we will have one API pXd_leaf() to detect all kinds of huge mappings. AFAICT we need to use the pXd_leaf() impl (rather than pXd_huge() ones) to make sure ie. THPs on hash MMU will also return true. This helps to simplify a follow up patch to drop pXd_huge() treewide. Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Christophe Leroy <redacted> Cc: "Aneesh Kumar K.V" <aneesh.kumar@kernel.org> Cc: "Naveen N. Rao" <redacted> Cc: linuxppc-dev@lists.ozlabs.org Signed-off-by: Peter Xu <peterx@redhat.com> --- arch/powerpc/include/asm/book3s/64/pgtable-4k.h | 14 ++------------ 1 file changed, 2 insertions(+), 12 deletions(-)diff --git a/arch/powerpc/include/asm/book3s/64/pgtable-4k.h b/arch/powerpc/include/asm/book3s/64/pgtable-4k.h index 48f21820afe2..92545981bb49 100644 --- a/arch/powerpc/include/asm/book3s/64/pgtable-4k.h +++ b/arch/powerpc/include/asm/book3s/64/pgtable-4k.h@@ -8,22 +8,12 @@ #ifdef CONFIG_HUGETLB_PAGE static inline int pmd_huge(pmd_t pmd) { - /* - * leaf pte for huge page - */ - if (radix_enabled()) - return !!(pmd_raw(pmd) & cpu_to_be64(_PAGE_PTE)); - return 0; + return pmd_leaf(pmd); } static inline int pud_huge(pud_t pud) { - /* - * leaf pte for huge page - */ - if (radix_enabled()) - return !!(pud_raw(pud) & cpu_to_be64(_PAGE_PTE)); - return 0; + return pud_leaf(pud); }
This doesn't actually compile though. arch/powerpc/include/asm/book3s/64/pgtable-4k.h:11:16: error: implicit declaration of function ‘pmd_leaf’; did you mean ‘pgd_clear’? [-Werror=implicit-function-declaration] etc. To make it compile we'd need to relocate the pmd/pud_leaf() definitions:
diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
index df66dce8306f..fd7180fded75 100644
--- a/arch/powerpc/include/asm/book3s/64/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/64/pgtable.h@@ -262,6 +262,18 @@ extern unsigned long __kernel_io_end; extern struct page *vmemmap; extern unsigned long pci_io_base; + +#define pmd_leaf pmd_leaf +static inline bool pmd_leaf(pmd_t pmd) +{ + return !!(pmd_raw(pmd) & cpu_to_be64(_PAGE_PTE)); +} + +#define pud_leaf pud_leaf +static inline bool pud_leaf(pud_t pud) +{ + return !!(pud_raw(pud) & cpu_to_be64(_PAGE_PTE)); +} #endif /* __ASSEMBLY__ */ #include <asm/book3s/64/hash.h>
@@ -1436,20 +1448,5 @@ static inline bool is_pte_rw_upgrade(unsigned long old_val, unsigned long new_va return false; } -/* - * Like pmd_huge(), but works regardless of config options - */ -#define pmd_leaf pmd_leaf -static inline bool pmd_leaf(pmd_t pmd) -{ - return !!(pmd_raw(pmd) & cpu_to_be64(_PAGE_PTE)); -} - -#define pud_leaf pud_leaf -static inline bool pud_leaf(pud_t pud) -{ - return !!(pud_raw(pud) & cpu_to_be64(_PAGE_PTE)); -} - #endif /* __ASSEMBLY__ */ #endif /* _ASM_POWERPC_BOOK3S_64_PGTABLE_H_ */
cheers