x86/mm/fixmap: Generalize the GDT fixmap mechanism, introduce struct cpu_entry_area

Currently, the GDT is an ad-hoc array of pages, one per CPU, in the
fixmap.  Generalize it to be an array of a new 'struct cpu_entry_area'
so that we can cleanly add new things to it.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bpetkov@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Laight <David.Laight@aculab.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Eduardo Valentin <eduval@amazon.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: aliguori@amazon.com
Cc: daniel.gruss@iaik.tugraz.at
Cc: hughd@google.com
Cc: keescook@google.com
Link: https://lkml.kernel.org/r/20171204150605.563271721@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/include/asm/desc.h b/arch/x86/include/asm/desc.h
index 01fd944..f6f4284 100644 (file)
--- a/arch/x86/include/asm/desc.h
+++ b/arch/x86/include/asm/desc.h
@@ -60,17 +60,10 @@ static inline struct desc_struct *get_current_gdt_rw(void)
        return this_cpu_ptr(&gdt_page)->gdt;
 }
 
-/* Get the fixmap index for a specific processor */
-static inline unsigned int get_cpu_gdt_ro_index(int cpu)
-{
-       return FIX_GDT_REMAP_END - cpu;
-}
-
 /* Provide the fixmap address of the remapped GDT */
 static inline struct desc_struct *get_cpu_gdt_ro(int cpu)
 {
-       unsigned int idx = get_cpu_gdt_ro_index(cpu);
-       return (struct desc_struct *)__fix_to_virt(idx);
+       return (struct desc_struct *)&get_cpu_entry_area(cpu)->gdt;
 }
 
 /* Provide the current read-only GDT */

diff --git a/arch/x86/include/asm/fixmap.h b/arch/x86/include/asm/fixmap.h
index b0c505f..b61f024 100644 (file)
--- a/arch/x86/include/asm/fixmap.h
+++ b/arch/x86/include/asm/fixmap.h
@@ -44,6 +44,19 @@ extern unsigned long __FIXADDR_TOP;
                         PAGE_SIZE)
 #endif
 
+/*
+ * cpu_entry_area is a percpu region in the fixmap that contains things
+ * needed by the CPU and early entry/exit code.  Real types aren't used
+ * for all fields here to avoid circular header dependencies.
+ *
+ * Every field is a virtual alias of some other allocated backing store.
+ * There is no direct allocation of a struct cpu_entry_area.
+ */
+struct cpu_entry_area {
+       char gdt[PAGE_SIZE];
+};
+
+#define CPU_ENTRY_AREA_PAGES (sizeof(struct cpu_entry_area) / PAGE_SIZE)
 
 /*
  * Here we define all the compile-time 'special' virtual
@@ -101,8 +114,8 @@ enum fixed_addresses {
        FIX_LNW_VRTC,
 #endif
        /* Fixmap entries to remap the GDTs, one per processor. */
-       FIX_GDT_REMAP_BEGIN,
-       FIX_GDT_REMAP_END = FIX_GDT_REMAP_BEGIN + NR_CPUS - 1,
+       FIX_CPU_ENTRY_AREA_TOP,
+       FIX_CPU_ENTRY_AREA_BOTTOM = FIX_CPU_ENTRY_AREA_TOP + (CPU_ENTRY_AREA_PAGES * NR_CPUS) - 1,
 
 #ifdef CONFIG_ACPI_APEI_GHES
        /* Used for GHES mapping from assorted contexts */
@@ -191,5 +204,25 @@ void __init *early_memremap_decrypted_wp(resource_size_t phys_addr,
 void __early_set_fixmap(enum fixed_addresses idx,
                        phys_addr_t phys, pgprot_t flags);
 
+static inline unsigned int __get_cpu_entry_area_page_index(int cpu, int page)
+{
+       BUILD_BUG_ON(sizeof(struct cpu_entry_area) % PAGE_SIZE != 0);
+
+       return FIX_CPU_ENTRY_AREA_BOTTOM - cpu*CPU_ENTRY_AREA_PAGES - page;
+}
+
+#define __get_cpu_entry_area_offset_index(cpu, offset) ({              \
+       BUILD_BUG_ON(offset % PAGE_SIZE != 0);                          \
+       __get_cpu_entry_area_page_index(cpu, offset / PAGE_SIZE);       \
+       })
+
+#define get_cpu_entry_area_index(cpu, field)                           \
+       __get_cpu_entry_area_offset_index((cpu), offsetof(struct cpu_entry_area, field))
+
+static inline struct cpu_entry_area *get_cpu_entry_area(int cpu)
+{
+       return (struct cpu_entry_area *)__fix_to_virt(__get_cpu_entry_area_page_index(cpu, 0));
+}
+
 #endif /* !__ASSEMBLY__ */
 #endif /* _ASM_X86_FIXMAP_H */

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 22f5421..2cb394d 100644 (file)
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -466,12 +466,12 @@ void load_percpu_segment(int cpu)
        load_stack_canary_segment();
 }
 
-/* Setup the fixmap mapping only once per-processor */
-static inline void setup_fixmap_gdt(int cpu)
+/* Setup the fixmap mappings only once per-processor */
+static inline void setup_cpu_entry_area(int cpu)
 {
 #ifdef CONFIG_X86_64
        /* On 64-bit systems, we use a read-only fixmap GDT. */
-       pgprot_t prot = PAGE_KERNEL_RO;
+       pgprot_t gdt_prot = PAGE_KERNEL_RO;
 #else
        /*
         * On native 32-bit systems, the GDT cannot be read-only because
@@ -482,11 +482,11 @@ static inline void setup_fixmap_gdt(int cpu)
         * On Xen PV, the GDT must be read-only because the hypervisor requires
         * it.
         */
-       pgprot_t prot = boot_cpu_has(X86_FEATURE_XENPV) ?
+       pgprot_t gdt_prot = boot_cpu_has(X86_FEATURE_XENPV) ?
                PAGE_KERNEL_RO : PAGE_KERNEL;
 #endif
 
-       __set_fixmap(get_cpu_gdt_ro_index(cpu), get_cpu_gdt_paddr(cpu), prot);
+       __set_fixmap(get_cpu_entry_area_index(cpu, gdt), get_cpu_gdt_paddr(cpu), gdt_prot);
 }
 
 /* Load the original GDT from the per-cpu structure */
@@ -1589,7 +1589,7 @@ void cpu_init(void)
        if (is_uv_system())
                uv_cpu_init();
 
-       setup_fixmap_gdt(cpu);
+       setup_cpu_entry_area(cpu);
        load_fixmap_gdt(cpu);
 }
 
@@ -1651,7 +1651,7 @@ void cpu_init(void)
 
        fpu__init_cpu();
 
-       setup_fixmap_gdt(cpu);
+       setup_cpu_entry_area(cpu);
        load_fixmap_gdt(cpu);
 }
 #endif

diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c
index 2ccdaba..c245423 100644 (file)
--- a/arch/x86/xen/mmu_pv.c
+++ b/arch/x86/xen/mmu_pv.c
@@ -2272,7 +2272,7 @@ static void xen_set_fixmap(unsigned idx, phys_addr_t phys, pgprot_t prot)
 #endif
        case FIX_TEXT_POKE0:
        case FIX_TEXT_POKE1:
-       case FIX_GDT_REMAP_BEGIN ... FIX_GDT_REMAP_END:
+       case FIX_CPU_ENTRY_AREA_TOP ... FIX_CPU_ENTRY_AREA_BOTTOM:
                /* All local page mappings */
                pte = pfn_pte(phys, prot);
                break;