linux-kernel - [RFC][PATCH v2 10/21] x86/pti: Function to map per-cpu page-table entry

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Date:   Mon, 16 Nov 2020 15:47:46 +0100
From:   Alexandre Chartre <alexandre.chartre@...cle.com>
To:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        x86@...nel.org, dave.hansen@...ux.intel.com, luto@...nel.org,
        peterz@...radead.org, linux-kernel@...r.kernel.org,
        thomas.lendacky@....com, jroedel@...e.de
Cc:     konrad.wilk@...cle.com, jan.setjeeilers@...cle.com,
        junaids@...gle.com, oweisse@...gle.com, rppt@...ux.vnet.ibm.com,
        graf@...zon.de, mgross@...ux.intel.com, kuzuno@...il.com,
        alexandre.chartre@...cle.com
Subject: [RFC][PATCH v2 10/21] x86/pti: Function to map per-cpu page-table entry

Wrap the code used by PTI to map a per-cpu page-table entry into
a new function so that this code can be re-used to map other
per-cpu entries.

Signed-off-by: Alexandre Chartre <alexandre.chartre@...cle.com>
---
 arch/x86/mm/pti.c | 25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index ebc8cd2f1cd8..71ca245d7b38 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -428,6 +428,21 @@ static void __init pti_clone_p4d(unsigned long addr)
 	*user_p4d = *kernel_p4d;
 }
 
+/*
+ * Clone a single percpu page.
+ */
+static void __init pti_clone_percpu_page(void *addr)
+{
+	phys_addr_t pa = per_cpu_ptr_to_phys(addr);
+	pte_t *target_pte;
+
+	target_pte = pti_user_pagetable_walk_pte((unsigned long)addr);
+	if (WARN_ON(!target_pte))
+		return;
+
+	*target_pte = pfn_pte(pa >> PAGE_SHIFT, PAGE_KERNEL);
+}
+
 /*
  * Clone the CPU_ENTRY_AREA and associated data into the user space visible
  * page table.
@@ -448,16 +463,8 @@ static void __init pti_clone_user_shared(void)
 		 * This is done for all possible CPUs during boot to ensure
 		 * that it's propagated to all mms.
 		 */
+		pti_clone_percpu_page(&per_cpu(cpu_tss_rw, cpu));
 
-		unsigned long va = (unsigned long)&per_cpu(cpu_tss_rw, cpu);
-		phys_addr_t pa = per_cpu_ptr_to_phys((void *)va);
-		pte_t *target_pte;
-
-		target_pte = pti_user_pagetable_walk_pte(va);
-		if (WARN_ON(!target_pte))
-			return;
-
-		*target_pte = pfn_pte(pa >> PAGE_SHIFT, PAGE_KERNEL);
 	}
 }
 
-- 
2.18.4