linux-kernel - [PATCH 2/7] x86/gdt: Fix setup_fixmap

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Date:   Wed, 22 Mar 2017 14:32:30 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Thomas Garnier <thgarnie@...gle.com>,
        Andy Lutomirski <luto@...nel.org>
Subject: [PATCH 2/7] x86/gdt: Fix setup_fixmap_gdt() to use the correct PA

__pa() cannot be used on percpu pointers because they may be
virtually mapped.  Use per_cpu_ptr_to_phys() instead.

This fixes a boot crash on a some 32-bit configurations.  I assume
this is related to which allocation strategy is chosen by the percpu
core.

Fixes: 69218e47994d x86: ("Remap GDT tables in the fixmap section")
Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 arch/x86/include/asm/desc.h  | 6 ++++++
 arch/x86/kernel/cpu/common.c | 4 ++--
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/desc.h b/arch/x86/include/asm/desc.h
index ec05f9c1a62c..bde11696b893 100644
--- a/arch/x86/include/asm/desc.h
+++ b/arch/x86/include/asm/desc.h
@@ -98,6 +98,12 @@ static inline unsigned long get_current_gdt_ro_vaddr(void)
 	return (unsigned long)get_current_gdt_ro();
 }
 
+/* Provide the physical address of the GDT page. */
+static inline phys_addr_t get_cpu_gdt_paddr(unsigned int cpu)
+{
+	return per_cpu_ptr_to_phys(get_cpu_gdt_rw(cpu));
+}
+
 #ifdef CONFIG_X86_64
 
 static inline void pack_gate(gate_desc *gate, unsigned type, unsigned long func,
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index f8e22dbad86c..f6e20e2dbfa5 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -461,8 +461,8 @@ pgprot_t pg_fixmap_gdt_flags = PAGE_KERNEL;
 /* Setup the fixmap mapping only once per-processor */
 static inline void setup_fixmap_gdt(int cpu)
 {
-	__set_fixmap(get_cpu_gdt_ro_index(cpu),
-		     __pa(get_cpu_gdt_rw(cpu)), pg_fixmap_gdt_flags);
+	__set_fixmap(get_cpu_gdt_ro_index(cpu), get_cpu_gdt_paddr(cpu),
+		     pg_fixmap_gdt_flags);
 }
 
 /* Load the original GDT from the per-cpu structure */
-- 
2.9.3