[SRU,Bionic,Cosmic,3/3] powerpc/mm/radix: Only need the Nest MMU workaround for R -> RW transition

Message ID af1d8a2ded6dddc197285c662b19e00c1aa42415.1539273155.git.joseph.salisbury@canonical.com
State New
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Series
  • Fixes for LP:1792195
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Commit Message

Joseph Salisbury Oct. 11, 2018, 4:22 p.m.
From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>

BugLink: https://bugs.launchpad.net/bugs/1792195

The Nest MMU workaround is only needed for RW upgrades. Avoid doing
that for other PTE updates.

We also avoid clearing the PTE while marking it invalid. This is
because other page table walkers will find this PTE none and can
result in unexpected behaviour due to that. Instead we clear
_PAGE_PRESENT and set the software PTE bit _PAGE_INVALID.
pte_present() is already updated to check for both bits. This makes
sure page table walkers will find the PTE present and things like
pte_pfn(pte) returns the right value.

Based on an original patch from Benjamin Herrenschmidt <benh@kernel.crashing.org>

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
(cherry picked from commit f08d08f3db55452d31ba4a37c702da6245876b96)
Signed-off-by: Joseph Salisbury <joseph.salisbury@canonical.com>
---
 arch/powerpc/mm/pgtable-radix.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

Patch

diff --git a/arch/powerpc/mm/pgtable-radix.c b/arch/powerpc/mm/pgtable-radix.c
index 704362d..f767f7db 100644
--- a/arch/powerpc/mm/pgtable-radix.c
+++ b/arch/powerpc/mm/pgtable-radix.c
@@ -970,20 +970,22 @@  void radix__ptep_set_access_flags(struct vm_area_struct *vma, pte_t *ptep,
 	struct mm_struct *mm = vma->vm_mm;
 	unsigned long set = pte_val(entry) & (_PAGE_DIRTY | _PAGE_ACCESSED |
 					      _PAGE_RW | _PAGE_EXEC);
+
+	unsigned long change = pte_val(entry) ^ pte_val(*ptep);
 	/*
 	 * To avoid NMMU hang while relaxing access, we need mark
 	 * the pte invalid in between.
 	 */
-	if (atomic_read(&mm->context.copros) > 0) {
+	if ((change & _PAGE_RW) && atomic_read(&mm->context.copros) > 0) {
 		unsigned long old_pte, new_pte;
 
-		old_pte = __radix_pte_update(ptep, ~0, 0);
+		old_pte = __radix_pte_update(ptep, _PAGE_PRESENT, _PAGE_INVALID);
 		/*
 		 * new value of pte
 		 */
 		new_pte = old_pte | set;
 		radix__flush_tlb_page_psize(mm, address, psize);
-		__radix_pte_update(ptep, 0, new_pte);
+		__radix_pte_update(ptep, _PAGE_INVALID, new_pte);
 	} else {
 		__radix_pte_update(ptep, 0, set);
 		radix__flush_tlb_page_psize(mm, address, psize);