linux-kernel - [PATCH v2 05/22] powerpc/book3s64/hash: Use the pte

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Message-Id: <20200319035609.158654-6-aneesh.kumar@linux.ibm.com>
Date:   Thu, 19 Mar 2020 09:25:52 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
To:     linuxppc-dev@...ts.ozlabs.org, mpe@...erman.id.au,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kvm-ppc@...r.kernel.org
Cc:     npiggin@...il.com, paulus@...abs.org, leonardo@...ux.ibm.com,
        kirill@...temov.name,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
Subject: [PATCH v2 05/22] powerpc/book3s64/hash: Use the pte_t address from the caller

Don't fetch the pte value using lockless page table walk. Instead use the value from the
caller. hash_preload is called with ptl lock held. So it is safe to use the
pte_t address directly.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
---
 arch/powerpc/mm/book3s64/hash_utils.c | 27 +++++----------------------
 1 file changed, 5 insertions(+), 22 deletions(-)

diff --git a/arch/powerpc/mm/book3s64/hash_utils.c b/arch/powerpc/mm/book3s64/hash_utils.c
index e2a7873c7760..81b4130ceb05 100644
--- a/arch/powerpc/mm/book3s64/hash_utils.c
+++ b/arch/powerpc/mm/book3s64/hash_utils.c
@@ -1545,14 +1545,11 @@ static bool should_hash_preload(struct mm_struct *mm, unsigned long ea)
 }
 #endif
 
-static void hash_preload(struct mm_struct *mm, unsigned long ea,
+static void hash_preload(struct mm_struct *mm, pte_t *ptep, unsigned long ea,
 			 bool is_exec, unsigned long trap)
 {
-	int hugepage_shift;
 	unsigned long vsid;
 	pgd_t *pgdir;
-	pte_t *ptep;
-	unsigned long flags;
 	int rc, ssize, update_flags = 0;
 	unsigned long access = _PAGE_PRESENT | _PAGE_READ | (is_exec ? _PAGE_EXEC : 0);
 
@@ -1574,30 +1571,18 @@ static void hash_preload(struct mm_struct *mm, unsigned long ea,
 	vsid = get_user_vsid(&mm->context, ea, ssize);
 	if (!vsid)
 		return;
-	/*
-	 * Hash doesn't like irqs. Walking linux page table with irq disabled
-	 * saves us from holding multiple locks.
-	 */
-	local_irq_save(flags);
 
-	/*
-	 * THP pages use update_mmu_cache_pmd. We don't do
-	 * hash preload there. Hence can ignore THP here
-	 */
-	ptep = find_current_mm_pte(pgdir, ea, NULL, &hugepage_shift);
-	if (!ptep)
-		goto out_exit;
-
-	WARN_ON(hugepage_shift);
 #ifdef CONFIG_PPC_64K_PAGES
 	/* If either H_PAGE_4K_PFN or cache inhibited is set (and we are on
 	 * a 64K kernel), then we don't preload, hash_page() will take
 	 * care of it once we actually try to access the page.
 	 * That way we don't have to duplicate all of the logic for segment
 	 * page size demotion here
+	 * Called with  PTL held, hence can be sure the value won't change in
+	 * between.
 	 */
 	if ((pte_val(*ptep) & H_PAGE_4K_PFN) || pte_ci(*ptep))
-		goto out_exit;
+		return;
 #endif /* CONFIG_PPC_64K_PAGES */
 
 	/* Is that local to this CPU ? */
@@ -1622,8 +1607,6 @@ static void hash_preload(struct mm_struct *mm, unsigned long ea,
 				   mm_ctx_user_psize(&mm->context),
 				   mm_ctx_user_psize(&mm->context),
 				   pte_val(*ptep));
-out_exit:
-	local_irq_restore(flags);
 }
 
 /*
@@ -1674,7 +1657,7 @@ void update_mmu_cache(struct vm_area_struct *vma, unsigned long address,
 		return;
 	}
 
-	hash_preload(vma->vm_mm, address, is_exec, trap);
+	hash_preload(vma->vm_mm, ptep, address, is_exec, trap);
 }
 
 #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
-- 
2.24.1