Commit 073ebebd authored Jul 26, 2024 by David Hildenbrand Committed by Andrew Morton Sep 01, 2024

powerpc/8xx: document and enforce that split PT locks are not used

Right now, we cannot have split PT locks because 8xx does not support SMP.

But for the sake of documentation *why* 8xx is fine regarding what we
documented in huge_pte_lockptr(), let's just add code to enforce it at the
same time as documenting it.

This should also make everybody who wants to copy from the 8xx approach of
supporting such unusual ways of mapping hugetlb folios aware that it gets
tricky once multiple page tables are involved.

Link: https://lkml.kernel.org/r/20240726150728.3159964-4-david@redhat.com


Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Peter Xu <peterx@redhat.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

parent 188cac58

arch/powerpc/mm/pgtable.c

+6 −0

Original line number	Diff line number	Diff line
		@@ -297,6 +297,12 @@ int huge_ptep_set_access_flags(struct vm_area_struct *vma,
		}

		#if defined(CONFIG_PPC_8xx)

		#if defined(CONFIG_SPLIT_PTE_PTLOCKS) \|\| defined(CONFIG_SPLIT_PMD_PTLOCKS)
		/* We need the same lock to protect the PMD table and the two PTE tables. */
		#error "8M hugetlb folios are incompatible with split page table locks"
		#endif

		static void __set_huge_pte_at(pmd_t pmd, pte_t ptep, pte_basic_t val)
		{
		pte_basic_t entry = (pte_basic_t )ptep;