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From: Vineet Gupta <vgupta@kernel.org>
To: linux-snps-arc@lists.infradead.org
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Anshuman Khandual <anshuman.khandual@arm.com>,
	Mike Rapoport <rppt@kernel.org>, Vineet Gupta <vgupta@kernel.org>
Subject: [PATCH v2 18/19] ARC: mm: vmalloc sync from kernel to user table to update PMD ...
Date: Thu, 12 Aug 2021 16:37:52 -0700	[thread overview]
Message-ID: <20210812233753.104217-19-vgupta@kernel.org> (raw)
In-Reply-To: <20210812233753.104217-1-vgupta@kernel.org>

... not PGD

vmalloc() sets up the kernel page table (starting from @swapper_pg_dir).
But when vmalloc area is accessed in context of a user task, say opening
terminal in n_tty_open(), the user page tables need to be synced from
kernel page tables so that TLB entry is created in "user context".

The old code was doing this incorrectly, as it was updating the user pgd
entry (first level itself) to point to kernel pud table (2nd level),
effectively yanking away the entire user space translation with kernel one.

The correct way to do this is to ONLY update a user space pgd/pud/pmd entry
if it is not popluated already. This ensures that only the missing leaf
pmd entry gets updated to point to relevant kernel pte table.

From code change pov, we are chaging the pattern:

	p4d = p4d_offset(pgd, address);
	p4d_k = p4d_offset(pgd_k, address);
	if (!p4d_present(*p4d_k))
		goto bad_area;
	set_p4d(p4d, *p4d_k);

with
	p4d = p4d_offset(pgd, address);
	p4d_k = p4d_offset(pgd_k, address);
	if (p4d_none(*p4d_k))
		goto bad_area;
	if (!p4d_present(*p4d))
		set_p4d(p4d, *p4d_k);

Signed-off-by: Vineet Gupta <vgupta@kernel.org>
---
 arch/arc/mm/fault.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/arch/arc/mm/fault.c b/arch/arc/mm/fault.c
index f8994164fa36..5787c261c9a4 100644
--- a/arch/arc/mm/fault.c
+++ b/arch/arc/mm/fault.c
@@ -36,31 +36,31 @@ noinline static int handle_kernel_vaddr_fault(unsigned long address)
 	pgd = pgd_offset(current->active_mm, address);
 	pgd_k = pgd_offset_k(address);
 
-	if (!pgd_present(*pgd_k))
+	if (pgd_none (*pgd_k))
 		goto bad_area;
-
-	set_pgd(pgd, *pgd_k);
+	if (!pgd_present(*pgd))
+		set_pgd(pgd, *pgd_k);
 
 	p4d = p4d_offset(pgd, address);
 	p4d_k = p4d_offset(pgd_k, address);
-	if (!p4d_present(*p4d_k))
+	if (p4d_none(*p4d_k))
 		goto bad_area;
-
-	set_p4d(p4d, *p4d_k);
+	if (!p4d_present(*p4d))
+		set_p4d(p4d, *p4d_k);
 
 	pud = pud_offset(p4d, address);
 	pud_k = pud_offset(p4d_k, address);
-	if (!pud_present(*pud_k))
+	if (pud_none(*pud_k))
 		goto bad_area;
-
-	set_pud(pud, *pud_k);
+	if (!pud_present(*pud))
+		set_pud(pud, *pud_k);
 
 	pmd = pmd_offset(pud, address);
 	pmd_k = pmd_offset(pud_k, address);
-	if (!pmd_present(*pmd_k))
+	if (pmd_none(*pmd_k))
 		goto bad_area;
-
-	set_pmd(pmd, *pmd_k);
+	if (!pmd_present(*pmd))
+		set_pmd(pmd, *pmd_k);
 
 	/* XXX: create the TLB entry here */
 	return 0;
-- 
2.25.1


  parent reply	other threads:[~2021-08-12 23:39 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-12 23:37 [PATCH v2 00/19] ARC mm updates: support 3/4 levels and asm-generic/pgalloc Vineet Gupta
2021-08-12 23:37 ` [PATCH v2 01/19] ARC: mm: use SCRATCH_DATA0 register for caching pgdir in ARCv2 only Vineet Gupta
2021-08-15  9:27   ` Mike Rapoport
2021-08-16 19:45     ` Vineet Gupta
2021-08-12 23:37 ` [PATCH v2 02/19] ARC: mm: remove tlb paranoid code Vineet Gupta
2021-08-12 23:37 ` [PATCH v2 03/19] ARC: mm: move mmu/cache externs out to setup.h Vineet Gupta
2021-08-15  9:27   ` Mike Rapoport
2021-08-16 19:47     ` Vineet Gupta
2021-08-12 23:37 ` [PATCH v2 04/19] ARC: mm: Fixes to allow STRICT_MM_TYPECHECKS Vineet Gupta
2021-08-12 23:37 ` [PATCH v2 05/19] ARC: mm: Enable STRICT_MM_TYPECHECKS Vineet Gupta
2021-08-12 23:37 ` [PATCH v2 06/19] ARC: ioremap: use more commonly used PAGE_KERNEL based uncached flag Vineet Gupta
2021-08-12 23:37 ` [PATCH v2 07/19] ARC: mm: pmd_populate* to use the canonical set_pmd (and drop pmd_set) Vineet Gupta
2021-08-12 23:37 ` [PATCH v2 08/19] ARC: mm: switch pgtable_t back to struct page * Vineet Gupta
2021-08-13 10:45   ` kernel test robot
2021-08-13 14:25     ` Vineet Gupta
2021-08-12 23:37 ` [PATCH v2 09/19] ARC: mm: switch to asm-generic/pgalloc.h Vineet Gupta
2021-08-12 23:37 ` [PATCH v2 10/19] ARC: mm: non-functional code cleanup ahead of 3 levels Vineet Gupta
2021-08-12 23:37 ` [PATCH v2 11/19] ARC: mm: move MMU specific bits out of ASID allocator Vineet Gupta
2021-08-12 23:37 ` [PATCH v2 12/19] ARC: mm: move MMU specific bits out of entry code Vineet Gupta
2021-08-12 23:37 ` [PATCH v2 13/19] ARC: mm: disintegrate mmu.h (arcv2 bits out) Vineet Gupta
2021-08-13  4:01   ` kernel test robot
2021-08-13 14:48     ` Vineet Gupta
2021-08-12 23:37 ` [PATCH v2 14/19] ARC: mm: disintegrate pgtable.h into levels and flags Vineet Gupta
2021-08-12 23:37 ` [PATCH v2 15/19] ARC: mm: hack to allow 2 level build with 4 level code Vineet Gupta
2021-08-12 23:37 ` [PATCH v2 16/19] ARC: mm: support 3 levels of page tables Vineet Gupta
2021-08-15  9:27   ` Mike Rapoport
2021-08-16 19:53     ` Vineet Gupta
2021-08-17  5:03       ` Mike Rapoport
2021-08-12 23:37 ` [PATCH v2 17/19] ARC: mm: support 4 " Vineet Gupta
2021-08-12 23:37 ` Vineet Gupta [this message]
2021-08-12 23:37 ` [PATCH v2 19/19] ARC: mm: introduce _PAGE_TABLE to explicitly link pgd,pud,pmd entries Vineet Gupta
2021-08-15  9:26 ` [PATCH v2 00/19] ARC mm updates: support 3/4 levels and asm-generic/pgalloc Mike Rapoport
2021-08-16 19:58   ` Vineet Gupta
2021-08-17  5:04     ` Mike Rapoport

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