linux-kernel - [PATCH] x86/mm/kaiser: Use the other page_table

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Date:   Mon, 27 Nov 2017 09:59:06 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...capital.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H . Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH] x86/mm/kaiser: Use the other page_table_lock pattern

Subject: x86/mm/kaiser: Use the other page_table_lock pattern
From: Peter Zijlstra <peterz@...radead.org>
Date: Mon Nov 27 09:35:08 CET 2017

Use the other page_table_lock pattern; this removes the free from
under the lock, reducing worst case hold times and makes it a leaf
lock.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/mm/kaiser.c |   24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

--- a/arch/x86/mm/kaiser.c
+++ b/arch/x86/mm/kaiser.c
@@ -183,11 +183,13 @@ static pte_t *kaiser_shadow_pagetable_wa
 			return NULL;
 
 		spin_lock(&shadow_table_allocation_lock);
-		if (p4d_none(*p4d))
+		if (p4d_none(*p4d)) {
 			set_p4d(p4d, __p4d(_KERNPG_TABLE | __pa(new_pud_page)));
-		else
-			free_page(new_pud_page);
+			new_pud_page = 0;
+		}
 		spin_unlock(&shadow_table_allocation_lock);
+		if (new_pud_page)
+			free_page(new_pud_page);
 	}
 
 	pud = pud_offset(p4d, address);
@@ -202,11 +204,13 @@ static pte_t *kaiser_shadow_pagetable_wa
 			return NULL;
 
 		spin_lock(&shadow_table_allocation_lock);
-		if (pud_none(*pud))
+		if (pud_none(*pud)) {
 			set_pud(pud, __pud(_KERNPG_TABLE | __pa(new_pmd_page)));
-		else
-			free_page(new_pmd_page);
+			new_pmd_page = 0;
+		}
 		spin_unlock(&shadow_table_allocation_lock);
+		if (new_pmd_page)
+			free_page(new_pmd_page);
 	}
 
 	pmd = pmd_offset(pud, address);
@@ -221,11 +225,13 @@ static pte_t *kaiser_shadow_pagetable_wa
 			return NULL;
 
 		spin_lock(&shadow_table_allocation_lock);
-		if (pmd_none(*pmd))
+		if (pmd_none(*pmd)) {
 			set_pmd(pmd, __pmd(_KERNPG_TABLE  | __pa(new_pte_page)));
-		else
-			free_page(new_pte_page);
+			new_pte_page = 0;
+		}
 		spin_unlock(&shadow_table_allocation_lock);
+		if (new_pte_page)
+			free_page(new_pte_page);
 	}
 
 	pte = pte_offset_kernel(pmd, address);